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8640 KiB

Open AccessArticle

Improvement in Char Strength with an Open Cage Silsesquioxane Flame Retardant

by Yolanda Bautista, Ana Gozalbo, Sergio Mestre and Vicente Sanz

Materials 2017, 10(6), 567; https://doi.org/10.3390/ma10060567 - 23 May 2017

Cited by 8 | Viewed by 4059

Abstract

Different characterization techniques were used to study the hydrolysis and condensation reaction kinetics of 3-methacryloxypropyltrimethoxysilane (MAPTMS) to obtain open cage silsesquioxane oligomers. The formation of hydrogen bonds, which condition the chemical structures of the resulting products, was identified. Improved thermal and fire resistant [...] Read more.

Different characterization techniques were used to study the hydrolysis and condensation reaction kinetics of 3-methacryloxypropyltrimethoxysilane (MAPTMS) to obtain open cage silsesquioxane oligomers. The formation of hydrogen bonds, which condition the chemical structures of the resulting products, was identified. Improved thermal and fire resistant behavior of unsaturated polyester (UP) composites prepared with aluminium trihydroxide (ATH) and the synthesized oligomer were registered. Opened silsesquioxane structures also showed an improvement in the mechanical properties of the char formed after firing. Full article

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3988 KiB

Open AccessArticle

Collagen-Fibrinogen Lyophilised Scaffolds for Soft Tissue Regeneration

by Jennifer Shepherd, Daniel Bax, Serena Best and Ruth Cameron

Materials 2017, 10(6), 568; https://doi.org/10.3390/ma10060568 - 23 May 2017

Cited by 13 | Viewed by 6020

Abstract

A significant body of research has considered collagen as a scaffold material for soft tissue regeneration. The main structural component of extra-cellular matrix (ECM), collagen’s advantages over synthetic polymers are numerous. However, for applications where higher stiffness and stability are required, significant cross-linking [...] Read more.

A significant body of research has considered collagen as a scaffold material for soft tissue regeneration. The main structural component of extra-cellular matrix (ECM), collagen’s advantages over synthetic polymers are numerous. However, for applications where higher stiffness and stability are required, significant cross-linking may affect bioactivity. A carbodiimide (EDC) cross-linking route consumes carboxylate groups that are key to collagen’s essential cell recognition motifs (GxOGER). Fibrinogen was considered as a promising additive as it plays a key role in the process of wound repair and contains RGD integrin binding sites which bind to a variety of cells, growth factors and cytokines. Fibrinogen’s binding sites however, also contain the same carboxylate groups as collagen. We have successfully produced highly interconnected, porous collagen-fibrinogen scaffolds using a lyophilisation technique and micro-computed tomography demonstrated minimal influence of either fibrinogen content or cross-linking concentration on the scaffold structure. The specific biological effect of fibrinogen additions into cross-linked collagen are considered by using films as a model for the struts of bulk scaffolds. By considering various additions of fibrinogen to the collagen film with increasing degrees of cross-linking, this study demonstrates a significant biological advantage with fibrinogen addition across the cross-linking concentrations typically applied to collagen-based scaffolds. Full article

(This article belongs to the Special Issue Naturally-Derived Biomaterials and Biopolymers)

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6723 KiB

Open AccessArticle

Ageing, Shocks and Wear Mechanisms in ZTA and the Long-Term Performance of Hip Joint Materials

by Armelle Perrichon, Bernard Haochih Liu, Jérôme Chevalier, Laurent Gremillard, Bruno Reynard, Frédéric Farizon, Jiunn-Der Liao and Jean Geringer

Materials 2017, 10(6), 569; https://doi.org/10.3390/ma10060569 - 24 May 2017

Cited by 16 | Viewed by 4802

Abstract

The surface morphologies and microstructures of Zirconia Toughened Alumina (ZTA) femoral heads were analyzed following in vitro tests aiming to simulate in vivo degradation. Three phenomena potentially leading to degradation were investigated: shocks, friction and hydrothermal ageing. Shocks due to micro-separation created the [...] Read more.

The surface morphologies and microstructures of Zirconia Toughened Alumina (ZTA) femoral heads were analyzed following in vitro tests aiming to simulate in vivo degradation. Three phenomena potentially leading to degradation were investigated: shocks, friction and hydrothermal ageing. Shocks due to micro-separation created the main damage with the formation of wear stripes on the femoral head surfaces. Atomic Force Microscopy (AFM) images suggested the release of wear debris of various shapes and sizes through inter- and intra-granular cracks; some debris may have a size lower than 100 nm. A decrease in hardness and Young’s modulus was measured within the wear stripes by nanoindentation technique and was attributed to the presence of surface and sub-surface micro-cracks. Such micro-cracks mechanically triggered the zirconia phase transformation in those worn areas, which in return presumably reduced further crack propagation. In comparison with shocks, friction caused little wear degradation as observed from AFM images by scarce pullout of grains. The long-term resistance of the ZTA composite material against hydrothermal ageing is confirmed by the present observations. Full article

(This article belongs to the Special Issue Corrosion and Tribology of Biomaterials Used in Hip and Knee Arthroplasty)

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1913 KiB

Open AccessArticle

Transparent Electrodes Based on Silver Nanowire Networks: From Physical Considerations towards Device Integration

by Daniel Bellet, Mélanie Lagrange, Thomas Sannicolo, Sara Aghazadehchors, Viet Huong Nguyen, Daniel P. Langley, David Muñoz-Rojas, Carmen Jiménez, Yves Bréchet and Ngoc Duy Nguyen

Materials 2017, 10(6), 570; https://doi.org/10.3390/ma10060570 - 24 May 2017

Cited by 62 | Viewed by 8635

Abstract

The past few years have seen a considerable amount of research devoted to nanostructured transparent conducting materials (TCM), which play a pivotal role in many modern devices such as solar cells, flexible light-emitting devices, touch screens, electromagnetic devices, and flexible transparent thin film [...] Read more.

The past few years have seen a considerable amount of research devoted to nanostructured transparent conducting materials (TCM), which play a pivotal role in many modern devices such as solar cells, flexible light-emitting devices, touch screens, electromagnetic devices, and flexible transparent thin film heaters. Currently, the most commonly used TCM for such applications (ITO: Indium Tin oxide) suffers from two major drawbacks: brittleness and indium scarcity. Among emerging transparent electrodes, silver nanowire (AgNW) networks appear to be a promising substitute to ITO since such electrically percolating networks exhibit excellent properties with sheet resistance lower than 10 Ω/sq and optical transparency of 90%, fulfilling the requirements of most applications. In addition, AgNW networks also exhibit very good mechanical flexibility. The fabrication of these electrodes involves low-temperature processing steps and scalable methods, thus making them appropriate for future use as low-cost transparent electrodes in flexible electronic devices. This contribution aims to briefly present the main properties of AgNW based transparent electrodes as well as some considerations relating to their efficient integration in devices. The influence of network density, nanowire sizes, and post treatments on the properties of AgNW networks will also be evaluated. In addition to a general overview of AgNW networks, we focus on two important aspects: (i) network instabilities as well as an efficient Atomic Layer Deposition (ALD) coating which clearly enhances AgNW network stability and (ii) modelling to better understand the physical properties of these networks. Full article

(This article belongs to the Special Issue Advances in Transparent Conducting Materials)

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2340 KiB

Open AccessArticle

Bearing Fault Detection Based on Empirical Wavelet Transform and Correlated Kurtosis by Acoustic Emission

by Zheyu Gao, Jing Lin, Xiufeng Wang and Xiaoqiang Xu

Materials 2017, 10(6), 571; https://doi.org/10.3390/ma10060571 - 24 May 2017

Cited by 24 | Viewed by 5136

Abstract

Rolling bearings are widely used in rotating equipment. Detection of bearing faults is of great importance to guarantee safe operation of mechanical systems. Acoustic emission (AE), as one of the bearing monitoring technologies, is sensitive to weak signals and performs well in detecting [...] Read more.

Rolling bearings are widely used in rotating equipment. Detection of bearing faults is of great importance to guarantee safe operation of mechanical systems. Acoustic emission (AE), as one of the bearing monitoring technologies, is sensitive to weak signals and performs well in detecting incipient faults. Therefore, AE is widely used in monitoring the operating status of rolling bearing. This paper utilizes Empirical Wavelet Transform (EWT) to decompose AE signals into mono-components adaptively followed by calculation of the correlated kurtosis (CK) at certain time intervals of these components. By comparing these CK values, the resonant frequency of the rolling bearing can be determined. Then the fault characteristic frequencies are found by spectrum envelope. Both simulation signal and rolling bearing AE signals are used to verify the effectiveness of the proposed method. The results show that the new method performs well in identifying bearing fault frequency under strong background noise. Full article

(This article belongs to the Special Issue Structural Health Monitoring for Aerospace Applications 2017)

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15865 KiB

Open AccessArticle

Coaxial Electrospinning and Characterization of Core-Shell Structured Cellulose Nanocrystal Reinforced PMMA/PAN Composite Fibers

by Chao Li, Qingde Li, Xiaohui Ni, Guoxiang Liu, Wanli Cheng and Guangping Han

Materials 2017, 10(6), 572; https://doi.org/10.3390/ma10060572 - 24 May 2017

Cited by 36 | Viewed by 7365

Abstract

A modified coaxial electrospinning process was used to prepare composite nanofibrous mats from a poly(methyl methacrylate) (PMMA) solution with the addition of different cellulose nanocrystals (CNCs) as the sheath fluid and polyacrylonitrile (PAN) solution as the core fluid. This study investigated the conductivity [...] Read more.

A modified coaxial electrospinning process was used to prepare composite nanofibrous mats from a poly(methyl methacrylate) (PMMA) solution with the addition of different cellulose nanocrystals (CNCs) as the sheath fluid and polyacrylonitrile (PAN) solution as the core fluid. This study investigated the conductivity of the as-spun solutions that increased significantly with increasing CNCs addition, which favors forming uniform fibers. This study discussed the effect of different CNCs addition on the morphology, thermal behavior, and the multilevel structure of the coaxial electrospun PMMA + CNCs/PAN composite nanofibers. A morphology analysis of the nanofibrous mats clearly demonstrated that the CNCs facilitated the production of the composite nanofibers with a core-shell structure. The diameter of the composite nanofibers decreased and the uniformity increased with increasing CNCs concentrations in the shell fluid. The composite nanofibrous mats had the maximum thermal decomposition temperature that was substantially higher than electrospun pure PMMA, PAN, as well as the core-shell PMMA/PAN nanocomposite. The BET (Brunauer, Emmett and Teller) formula results showed that the specific surface area of the CNCs reinforced core-shell composite significantly increased with increasing CNCs content. The specific surface area of the composite with 20% CNCs loading rose to 9.62 m²/g from 3.76 m²/g for the control. A dense porous structure was formed on the surface of the electrospun core-shell fibers. Full article

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1647 KiB

Open AccessArticle

Cerium Chloride Application Promotes Wound Healing and Cell Proliferation in Human Foreskin Fibroblasts

by Liza L. Ramenzoni, Franz E. Weber, Thomas Attin and Patrick R. Schmidlin

Materials 2017, 10(6), 573; https://doi.org/10.3390/ma10060573 - 24 May 2017

Cited by 22 | Viewed by 3973

Abstract

This study investigated the effect of cerium chloride (CeCl₃) on cell migration and gene expression of human foreskin fibroblasts (HFF). HFF were exposed to three different CeCl₃ solutions (1%, 5% and 10%, w/v %) for three different time [...] Read more.

This study investigated the effect of cerium chloride (CeCl₃) on cell migration and gene expression of human foreskin fibroblasts (HFF). HFF were exposed to three different CeCl₃ solutions (1%, 5% and 10%, w/v %) for three different time durations (1, 5 and 10 min). 72 h after exposure to CeCl₃, cell viability was assessed by MTT test. A scratch-wounded assay determined the cell migration and the width of the wound, measured at 24 h. Gene expression patterns for cyclins B1, D1 and E1 were analyzed by RT-PCR (p < 0.05, t-test). The viability proliferation increased at 1- and 5-min exposures for all CeCl₃ concentrations, in contrast to no treatment (p < 0.05 at 24 h). No influence of CeCl₃ was found after 10 min. The scratch assay showed increased cell migration up to 60% at 1 and 5 min after 24 h at 5% and 10%. Cyclin B1, D1 and E1 all showed upregulation, confirming an increase in cell proliferation. This study demonstrates that exposure time and concentration of CeCl₃ may have a positive effect on fibroblast viability and migration. Application of CeCl₃ may be beneficial as a cell-stimulating agent leading to therapeutic tissue fibrosis or more resistant tissue around teeth, when warranted, during different periodontal therapies. Full article

(This article belongs to the Section Biomaterials)

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3745 KiB

Open AccessArticle

The Rejuvenating Effect in Hot Asphalt Recycling by Mortar Transfer Ratio and Image Analysis

by Fusong Wang, Zipeng Wang, Chao Li, Yue Xiao, Shaopeng Wu and Pan Pan

Materials 2017, 10(6), 574; https://doi.org/10.3390/ma10060574 - 24 May 2017

Cited by 22 | Viewed by 4436

Abstract

Using a rejuvenator to improve the performance of asphalt pavement is an effective and economic way of hot asphalt recycling. This research analyzes the rejuvenating effect on aged asphalt by means of a Mortar Transfer Ratio (MTR) test, which concerns the ratio of [...] Read more.

Using a rejuvenator to improve the performance of asphalt pavement is an effective and economic way of hot asphalt recycling. This research analyzes the rejuvenating effect on aged asphalt by means of a Mortar Transfer Ratio (MTR) test, which concerns the ratio of asphalt mortar that moves from recycled aggregates (RAP aggregates) to fresh added aggregates when aged asphalt is treated with a regenerating agent and comes into contact with fresh aggregates. The proposed MTR test analyzes the regeneration in terms of the softening degree on aged asphalt when the rejuvenator is applied. The covered area ratio is studied with an image analyzing tool to understand the possibility of mortar transferring from RAP aggregates to fresh aggregates. Additionally, a micro-crack closure test is conducted and observed through a microscope. The repairing ability and diffusion characteristics of micro-cracks can therefore be analyzed. The test results demonstrate that the proposed mortar transfer ratio is a feasible way to evaluate rejuvenator diffusion during hot recycling. The mortar transfer ratio and uncovered area ratio on fresh aggregates are compatible, and can be used to quantify the contribution of the rejuvenator. Within a certain temperature range, the diffusing effect of the rejuvenator is better when the diffusing temperature is higher. The diffusion time of the rejuvenator is optimum when diffusion occurs for 4–8 h. When the rejuvenator is properly applied, the rough and cracking surface can be repaired, resulting in better covered aggregates. The micro-closure analysis visually indicates that rejuvenators can be used to repair the RAP aggregates during hot recycling. Full article

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1838 KiB

Open AccessFeature PaperArticle

A Re-Evaluation of the Causes of Deformation in 1Cr-1Mo-0.25V Steel for Turbine Rotors and Shafts Based on iso-Thermal Plots of the Wilshire Equation and the Modelling of Batch to Batch Variation

by Mark Evans

Materials 2017, 10(6), 575; https://doi.org/10.3390/ma10060575 - 24 May 2017

Cited by 4 | Viewed by 4117

Abstract

The aims of this paper were to: (a) demonstrate how iso-thermal plots of the Wilshire equation can be used to identify the correct structure of this equation (which in turn enables a meaningful description of the creep mechanism involved in deformation to be [...] Read more.

The aims of this paper were to: (a) demonstrate how iso-thermal plots of the Wilshire equation can be used to identify the correct structure of this equation (which in turn enables a meaningful description of the creep mechanism involved in deformation to be made); and (b) show how a generalized specification of batch to batch variation could produce less conservative predictions of the time to failure associated with a given degree of risk. Such predictions were obtained using maximum likelihood estimation of the parameters of a generalised F distribution. It was found that the original Wilshire-Scharning assumption of a constant activation energy for this materials is incorrect. Consequently, their interpretation of deformation being due only to dislocation creep with deteriorating microstructure at long duration test times appears to be ill founded, with the varying activation energy suggesting instead that deformation is due to grain boundary sliding accommodated by either dislocation and diffusional creep with dominance changing from the lattice to the grain boundaries as the temperature changes. Modelling batch to batch variation as a function of stress also resulted in a 50% extended safe life prediction (corresponding to a 1% chance of failure) at 873 K and 47 MPa. Full article

(This article belongs to the Special Issue The Life of Materials at High Temperatures)

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8180 KiB

Open AccessFeature PaperArticle

Transport in Proton Exchange Membranes for Fuel Cell Applications—A Systematic Non-Equilibrium Approach

by Angie L. Rangel-Cárdenas and Ger J. M Koper

Materials 2017, 10(6), 576; https://doi.org/10.3390/ma10060576 - 25 May 2017

Cited by 25 | Viewed by 5714

Abstract

We hypothesize that the properties of proton-exchange membranes for fuel cell applications cannot be described unambiguously unless interface effects are taken into account. In order to prove this, we first develop a thermodynamically consistent description of the transport properties in the membranes, both [...] Read more.

We hypothesize that the properties of proton-exchange membranes for fuel cell applications cannot be described unambiguously unless interface effects are taken into account. In order to prove this, we first develop a thermodynamically consistent description of the transport properties in the membranes, both for a homogeneous membrane and for a homogeneous membrane with two surface layers in contact with the electrodes or holder material. For each subsystem, homogeneous membrane, and the two surface layers, we limit ourselves to four parameters as the system as a whole is considered to be isothermal. We subsequently analyze the experimental results on some standard membranes that have appeared in the literature and analyze these using the two different descriptions. This analysis yields relatively well-defined values for the homogeneous membrane parameters and estimates for those of the surface layers and hence supports our hypothesis. As demonstrated, the method used here allows for a critical evaluation of the literature values. Moreover, it allows optimization of stacked transport systems such as proton-exchange membrane fuel cell units where interfacial layers, such as that between the catalyst and membrane, are taken into account systematically. Full article

(This article belongs to the Special Issue Advanced Materials in Polymer Electrolyte Fuel Cells)

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878 KiB

Open AccessArticle

Influence of the Constitutive Model for Shotcrete on the Predicted Structural Behavior of the Shotcrete Shell of a Deep Tunnel

by Matthias Neuner, Magdalena Schreter, David Unteregger and Günter Hofstetter

Materials 2017, 10(6), 577; https://doi.org/10.3390/ma10060577 - 25 May 2017

Cited by 18 | Viewed by 4293

Abstract

The aim of the present paper is to investigate the influence of the constitutive model for shotcrete on the predicted displacements and stresses in shotcrete shells of deep tunnels. Previously proposed shotcrete models as well as a new extended damage plasticity model for [...] Read more.

The aim of the present paper is to investigate the influence of the constitutive model for shotcrete on the predicted displacements and stresses in shotcrete shells of deep tunnels. Previously proposed shotcrete models as well as a new extended damage plasticity model for shotcrete are evaluated in the context of 2D finite element simulations of the excavation of a stretch of a deep tunnel by means of the New Austrian Tunneling Method. Thereby, the behavior of the surrounding rock mass is described by the commonly used Hoek–Brown model. Differences in predicted evolutions of displacements and stresses in the shotcrete shell, resulting from the different shotcrete models, are discussed and simulation results are compared to available in situ measurement data. Full article

(This article belongs to the Special Issue Computational Mechanics of Cohesive-Frictional Materials)

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6772 KiB

Open AccessArticle

Magnetic and Structural Properties of Barium Hexaferrite BaFe₁₂O₁₉ from Various Growth Techniques

by Denis A. Vinnik, Aleksandra Yu. Tarasova, Dmitry A. Zherebtsov, Svetlana A. Gudkova, Damir M. Galimov, Vladimir E. Zhivulin, Evgeny A. Trofimov, Sandra Nemrava, Nikolai S. Perov, Ludmila I. Isaenko and Rainer Niewa

Materials 2017, 10(6), 578; https://doi.org/10.3390/ma10060578 - 25 May 2017

Cited by 43 | Viewed by 6629

Abstract

Barium hexaferrite powder samples with grains in the μm-range were obtained from solid-state sintering, and crystals with sizes up to 5 mm grown from PbO, Na₂CO₃, and BaB₂O₄ fluxes, respectively. Carbonate and borate fluxes provide the [...] Read more.

Barium hexaferrite powder samples with grains in the μm-range were obtained from solid-state sintering, and crystals with sizes up to 5 mm grown from PbO, Na₂CO₃, and BaB₂O₄ fluxes, respectively. Carbonate and borate fluxes provide the largest and structurally best crystals at significantly lower growth temperatures of 1533 K compared to flux-free synthesis (1623 K). The maximum synthesis temperature can be further reduced by the application of PbO-containing fluxes (down to 1223 K upon use of 80 at % PbO), however, Pb-substituted crystals Ba_1–xPb_xFe₁₂O₁₉ with Pb contents in the range of 0.23(2) ≤ x ≤ 0.80(2) form, depending on growth temperature and flux PbO content. The degree of Pb-substitution has only a minor influence on unit cell and magnetic parameters, although the values for Curie temperature, saturation magnetization, as well as the coercivity of these samples are significantly reduced in comparison with those from samples obtained from the other fluxes. Due to the lowest level of impurities, the samples from carbonate flux show superior quality compared to materials obtained using other methods. Full article

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10270 KiB

Open AccessArticle

Chemical Treatment of Waste Abaca for Natural Fiber-Reinforced Geopolymer Composite

by Roy Alvin J. Malenab, Janne Pauline S. Ngo and Michael Angelo B. Promentilla

Materials 2017, 10(6), 579; https://doi.org/10.3390/ma10060579 - 25 May 2017

Cited by 96 | Viewed by 11956

Abstract

The use of natural fibers in reinforced composites to produce eco-friendly materials is gaining more attention due to their attractive features such as low cost, low density and good mechanical properties, among others. This work thus investigates the potential of waste abaca (Manila [...] Read more.

The use of natural fibers in reinforced composites to produce eco-friendly materials is gaining more attention due to their attractive features such as low cost, low density and good mechanical properties, among others. This work thus investigates the potential of waste abaca (Manila hemp) fiber as reinforcing agent in an inorganic aluminosilicate material known as geopolymer. In this study, the waste fibers were subjected to different chemical treatments to modify the surface characteristics and to improve the adhesion with the fly ash-based geopolymer matrix. Definitive screening design of experiment was used to investigate the effect of successive chemical treatment of the fiber on its tensile strength considering the following factors: (1) NaOH pretreatment; (2) soaking time in aluminum salt solution; and (3) final pH of the slurry. The results show that the abaca fiber without alkali pretreatment, soaked for 12 h in Al₂(SO₄)₃ solution and adjusted to pH 6 exhibited the highest tensile strength among the treated fibers. Test results confirmed that the chemical treatment removes the lignin, pectin and hemicellulose, as well as makes the surface rougher with the deposition of aluminum compounds. This improves the interfacial bonding between geopolymer matrix and the abaca fiber, while the geopolymer protects the treated fiber from thermal degradation. Full article

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4165 KiB

Open AccessArticle

Carbon-Supported Pd and PdFe Alloy Catalysts for Direct Methanol Fuel Cell Cathodes

by Luis M. Rivera Gavidia, David Sebastián, Elena Pastor, Antonino S. Aricò and Vincenzo Baglio

Materials 2017, 10(6), 580; https://doi.org/10.3390/ma10060580 - 25 May 2017

Cited by 27 | Viewed by 6328

Abstract

Direct methanol fuel cells (DMFCs) are electrochemical devices that efficiently produce electricity and are characterized by a large flexibility for portable applications and high energy density. Methanol crossover is one of the main obstacles for DMFC commercialization, forcing the search for highly electro-active [...] Read more.

Direct methanol fuel cells (DMFCs) are electrochemical devices that efficiently produce electricity and are characterized by a large flexibility for portable applications and high energy density. Methanol crossover is one of the main obstacles for DMFC commercialization, forcing the search for highly electro-active and methanol tolerant cathodes. In the present work, carbon-supported Pd and PdFe catalysts were synthesized using a sodium borohydride reduction method and physico-chemically characterized using transmission electron microscopy (TEM) and X-ray techniques such as photoelectron spectroscopy (XPS), diffraction (XRD) and energy dispersive spectroscopy (EDX). The catalysts were investigated as DMFC cathodes operating at different methanol concentrations (up to 10 M) and temperatures (60 °C and 90 °C). The cell based on PdFe/C cathode presented the best performance, achieving a maximum power density of 37.5 mW·cm⁻² at 90 °C with 10 M methanol, higher than supported Pd and Pt commercial catalysts, demonstrating that Fe addition yields structural changes to Pd crystal lattice that reduce the crossover effects in DMFC operation. Full article

(This article belongs to the Special Issue Advanced Materials in Polymer Electrolyte Fuel Cells)

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1224 KiB

Open AccessCommunication

Alizarin Red S-Confined Layer-By-Layer Films as Redox-Active Coatings on Electrodes for the Voltammetric Determination of L-Dopa

by Shigehiro Takahashi, Iwao Suzuki, Tatsuro Sugawara, Masaru Seno, Daichi Minaki and Jun-Ichi Anzai

Materials 2017, 10(6), 581; https://doi.org/10.3390/ma10060581 - 25 May 2017

Cited by 9 | Viewed by 4272

Abstract

The preparation of redox-active coatings is a key step in fabricating electrochemical biosensors. To this goal, a variety of coating materials have been used in combination with redox-active compounds. In this study, alizarin red S (ARS) was confined in layer-by-layer (LbL) films composed [...] Read more.

The preparation of redox-active coatings is a key step in fabricating electrochemical biosensors. To this goal, a variety of coating materials have been used in combination with redox-active compounds. In this study, alizarin red S (ARS) was confined in layer-by-layer (LbL) films composed of poly(ethyleneimine) (PEI) and carboxymethylcellulose (CMC) to study the redox properties. A gold (Au) disc electrode coated with PEI/CMC LbL film was immersed in an ARS solution to uptake ARS into the film. ARS was successfully confined in the LbL film through electrostatic interactions. The cyclic voltammogram (CV) of ARS-confined PEI/CMC film-coated electrodes thus prepared exhibited redox waves in the potential range from −0.5 to −0.7 V originating from 9,10-anthraquinone moiety in ARS, demonstrating that ARS preserves its redox activity in the LbL film. An additional oxidation peak appeared around −0.4 V in the CV recorded in the solution containing phenylboronic acid (PBA), due to the formation of a boronate ester of ARS (ARS-PBA) in the film. The oxidation peak current at −0.4 V decreased upon addition of 3,4-dihydroxyphenylalanine (L-dopa) to the solution. Thus, the results suggest a potential use of the ARS-confined PEI/CMC films for constructing voltammetric sensors for L-dopa. Full article

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8191 KiB

Open AccessArticle

Fault Diagnosis for Rolling Bearings under Variable Conditions Based on Visual Cognition

by Yujie Cheng, Bo Zhou, Chen Lu and Chao Yang

Materials 2017, 10(6), 582; https://doi.org/10.3390/ma10060582 - 25 May 2017

Cited by 13 | Viewed by 4476

Abstract

Fault diagnosis for rolling bearings has attracted increasing attention in recent years. However, few studies have focused on fault diagnosis for rolling bearings under variable conditions. This paper introduces a fault diagnosis method for rolling bearings under variable conditions based on visual cognition. [...] Read more.

Fault diagnosis for rolling bearings has attracted increasing attention in recent years. However, few studies have focused on fault diagnosis for rolling bearings under variable conditions. This paper introduces a fault diagnosis method for rolling bearings under variable conditions based on visual cognition. The proposed method includes the following steps. First, the vibration signal data are transformed into a recurrence plot (RP), which is a two-dimensional image. Then, inspired by the visual invariance characteristic of the human visual system (HVS), we utilize speed up robust feature to extract fault features from the two-dimensional RP and generate a 64-dimensional feature vector, which is invariant to image translation, rotation, scaling variation, etc. Third, based on the manifold perception characteristic of HVS, isometric mapping, a manifold learning method that can reflect the intrinsic manifold embedded in the high-dimensional space, is employed to obtain a low-dimensional feature vector. Finally, a classical classification method, support vector machine, is utilized to realize fault diagnosis. Verification data were collected from Case Western Reserve University Bearing Data Center, and the experimental result indicates that the proposed fault diagnosis method based on visual cognition is highly effective for rolling bearings under variable conditions, thus providing a promising approach from the cognitive computing field. Full article

(This article belongs to the Special Issue Structural Health Monitoring for Aerospace Applications 2017)

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1678 KiB

Open AccessArticle

Photoelectric Properties of Si Doping Superlattice Structure on 6H-SiC(0001)

by Lianbi Li, Yuan Zang, Jichao Hu, Shenghuang Lin and Zhiming Chen

Materials 2017, 10(6), 583; https://doi.org/10.3390/ma10060583 - 25 May 2017

Cited by 1 | Viewed by 3812

Abstract

The energy-band structure and visible photoelectric properties of a p/n-Si doping superlattice structure (DSL) on 6H-SiC were simulated by Silvaco-TCAD. The,n the Si-DSL structures with 40 nm-p-Si/50 nm-n-Si multilayers were successfully prepared on 6H-SiC(0001) Si-face by chemical vapor deposition. TEM characterizations of the [...] Read more.

The energy-band structure and visible photoelectric properties of a p/n-Si doping superlattice structure (DSL) on 6H-SiC were simulated by Silvaco-TCAD. The,n the Si-DSL structures with 40 nm-p-Si/50 nm-n-Si multilayers were successfully prepared on 6H-SiC(0001) Si-face by chemical vapor deposition. TEM characterizations of the p/n-Si DSL confirmed the epitaxial growth of the Si films with preferred orientation and the misfit dislocations with a Burgers vector of 1/3 <21-1> at the p-Si/n-Si interface. The device had an obvious rectifying behavior, and the turn-on voltage was about 1.2 V. Under the visible illumination of 0.6 W/cm², the device demonstrated a significant photoelectric response with a photocurrent density of 2.1 mA/cm². Visible light operation of the Si-DSL/6H-SiC heterostructure was realized for the first time. Full article

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2343 KiB

Open AccessArticle

A Constitutive Model for Soft Clays Incorporating Elastic and Plastic Cross-Anisotropy

by Jorge Castro and Nallathamby Sivasithamparam

Materials 2017, 10(6), 584; https://doi.org/10.3390/ma10060584 - 25 May 2017

Cited by 8 | Viewed by 5180

Abstract

Natural clays exhibit a significant degree of anisotropy in their fabric, which initially is derived from the shape of the clay platelets, deposition process and one-dimensional consolidation. Various authors have proposed anisotropic elastoplastic models involving an inclined yield surface to reproduce anisotropic behavior [...] Read more.

Natural clays exhibit a significant degree of anisotropy in their fabric, which initially is derived from the shape of the clay platelets, deposition process and one-dimensional consolidation. Various authors have proposed anisotropic elastoplastic models involving an inclined yield surface to reproduce anisotropic behavior of plastic nature. This paper presents a novel constitutive model for soft structured clays that includes anisotropic behavior both of elastic and plastic nature. The new model incorporates stress-dependent cross-anisotropic elastic behavior within the yield surface using three independent elastic parameters because natural clays exhibit cross-anisotropic (or transversely isotropic) behavior after deposition and consolidation. Thus, the model only incorporates an additional variable with a clear physical meaning, namely the ratio between horizontal and vertical stiffnesses, which can be analytically obtained from conventional laboratory tests. The model does not consider evolution of elastic anisotropy, but laboratory results show that large strains are necessary to cause noticeable changes in elastic anisotropic behavior. The model is able to capture initial non-vertical effective stress paths for undrained triaxial tests and to predict deviatoric strains during isotropic loading or unloading. Full article

(This article belongs to the Special Issue Computational Mechanics of Cohesive-Frictional Materials)

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7756 KiB

Open AccessArticle

The Effect of Modulation Ratio of Cu/Ni Multilayer Films on the Fretting Damage Behaviour of Ti-811 Titanium Alloy

by Xiaohua Zhang, Daoxin Liu, Xiaoying Li, Hanshan Dong and Yuntao Xi

Materials 2017, 10(6), 585; https://doi.org/10.3390/ma10060585 - 26 May 2017

Cited by 5 | Viewed by 3448

Abstract

To improve the fretting damage (fretting wear and fretting fatigue) resistance of Ti-811 titanium alloy, three Cu/Ni multilayer films with the same modulation period thickness (200 nm) and different modulation ratios (3:1, 1:1, 1:3) were deposited on the surface of the alloy via [...] Read more.

To improve the fretting damage (fretting wear and fretting fatigue) resistance of Ti-811 titanium alloy, three Cu/Ni multilayer films with the same modulation period thickness (200 nm) and different modulation ratios (3:1, 1:1, 1:3) were deposited on the surface of the alloy via ion-assisted magnetron sputtering deposition (IAD). The bonding strength, micro-hardness, and toughness of the films were evaluated, and the effect of the modulation ratio on the room-temperature fretting wear (FW) and fretting fatigue (FF) resistance of the alloy was determined. The results indicated that the IAD technique can be successfully used to prepare Cu/Ni multilayer films, with high bonding strength, low-friction, and good toughness, which yield improved room-temperature FF and FW resistance of the alloy. For the same modulation period (200 nm), the micro-hardness, friction, and FW resistance of the coated alloy increased, decreased, and improved, respectively, with increasing modulation ratio of the Ni-to-Cu layer thickness. However, the FF resistance of the coated alloy increased non-monotonically with the increasing modulation ratio. Among the three Cu/Ni multilayer films, those with a modulation ratio of 1:1 can confer the highest FF resistance to the Ti-811 alloy, owing mainly to their unique combination of good toughness, high strength, and low-friction. Full article

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Open AccessArticle

Influence of Electrical and Ionic Conductivities of Organic Electronic Ion Pump on Acetylcholine Exchange Performance

by Nazrin Abdullayeva and Mehmet Sankir

Materials 2017, 10(6), 586; https://doi.org/10.3390/ma10060586 - 26 May 2017

Cited by 13 | Viewed by 4400

Abstract

By using an easy and effective method of depositing conjugated polymers (PEDOT:PSS) on flexible substrates, a new design for organic bioelectronic devices has been developed. The purpose was to build up a system that mimics the motion of neurotransmitters in the synaptic cleft [...] Read more.

By using an easy and effective method of depositing conjugated polymers (PEDOT:PSS) on flexible substrates, a new design for organic bioelectronic devices has been developed. The purpose was to build up a system that mimics the motion of neurotransmitters in the synaptic cleft by obtaining an electrical to chemical signal transport. Fourier transform infrared (FTIR) spectroscopy and Raman measurements have demonstrated that electrochemical overoxidation region which separates the pristine PEDOT:PSS electrodes and allows ionic conduction has been achieved successfully. The influence of both electrical and ionic conductivities on organic electronic ion pump (OEIP) performances has been studied. The ultimate goal was to achieve the highest equilibrium current density at the lowest applied voltage via enhancing the electrical conductivity of PEDOT:PSS and ionic conductivity of electrochemically overoxidized region. The highest equilibrium current density, which corresponds to 4.81 × 10¹⁷ number of ions of acetylcholine was about 41 μA cm⁻² observed for the OEIP with the electrical conductivities of 54 S cm⁻¹. This was a threshold electrical conductivity beyond which the OEIP performances were not changed much. Once Nafion™ has been applied for enhancing the ionic conductivity, the equilibrium current density increased about ten times and reached up to 408 μA cm⁻². Therefore, it has been demonstrated that the OEIP performance mainly scales with the ionic conductivity. A straightforward method of producing organic bioelectronics is proposed here may provide a clue for their effortless mass production in the near future. Full article

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Open AccessArticle

Modeling Framework for Fracture in Multiscale Cement-Based Material Structures

by Zhiwei Qian, Erik Schlangen, Guang Ye and Klaas Van Breugel

Materials 2017, 10(6), 587; https://doi.org/10.3390/ma10060587 - 26 May 2017

Cited by 46 | Viewed by 5196

Abstract

Multiscale modeling for cement-based materials, such as concrete, is a relatively young subject, but there are already a number of different approaches to study different aspects of these classical materials. In this paper, the parameter-passing multiscale modeling scheme is established and applied to [...] Read more.

Multiscale modeling for cement-based materials, such as concrete, is a relatively young subject, but there are already a number of different approaches to study different aspects of these classical materials. In this paper, the parameter-passing multiscale modeling scheme is established and applied to address the multiscale modeling problem for the integrated system of cement paste, mortar, and concrete. The block-by-block technique is employed to solve the length scale overlap challenge between the mortar level (0.1–10 mm) and the concrete level (1–40 mm). The microstructures of cement paste are simulated by the HYMOSTRUC3D model, and the material structures of mortar and concrete are simulated by the Anm material model. Afterwards the 3D lattice fracture model is used to evaluate their mechanical performance by simulating a uniaxial tensile test. The simulated output properties at a lower scale are passed to the next higher scale to serve as input local properties. A three-level multiscale lattice fracture analysis is demonstrated, including cement paste at the micrometer scale, mortar at the millimeter scale, and concrete at centimeter scale. Full article

(This article belongs to the Special Issue Numerical Analysis of Concrete using Discrete Elements)

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Open AccessArticle

Investigation on Characteristic Variation of the FBG Spectrum with Crack Propagation in Aluminum Plate Structures

by Bo Jin, Weifang Zhang, Meng Zhang, Feifei Ren, Wei Dai and Yanrong Wang

Materials 2017, 10(6), 588; https://doi.org/10.3390/ma10060588 - 27 May 2017

Cited by 12 | Viewed by 4615

Abstract

In order to monitor the crack tip propagation of aluminum alloy, this study investigates the variation of the spectrum characteristics of a fiber Bragg grating (FBG), combined with an analysis of the spectrum simulation. The results identify the location of the subordinate peak [...] Read more.

In order to monitor the crack tip propagation of aluminum alloy, this study investigates the variation of the spectrum characteristics of a fiber Bragg grating (FBG), combined with an analysis of the spectrum simulation. The results identify the location of the subordinate peak as significantly associated with the strain distribution along the grating, corresponding to the different plastic zones ahead of the crack tip with various crack lengths. FBG sensors could observe monotonic and cyclic plastic zones ahead of the crack tip, with the quadratic strain distribution along the grating at the crack tip-FBG distance of 1.2 and 0.7 mm, respectively. FBG sensors could examine the process zones ahead of the crack tip with the cubic strain distribution along the grating at the crack tip-FBG distance of 0.5 mm. The spectrum oscillation occurs as the crack approaches the FBG where the highly heterogeneous strain is distributed. Another idea is to use a finite element method (FEM), together with a T-matrix method, to analyze the reflection intensity spectra of FBG sensors for various crack sizes. The described crack propagation detection system may apply in structural health monitoring. Full article

(This article belongs to the Special Issue Structural Health Monitoring for Aerospace Applications 2017)

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Open AccessArticle

Crack Extension and Possibility of Debonding in Encapsulation-Based Self-Healing Materials

by Wenting Li, Zhengwu Jiang and Zhenghong Yang

Materials 2017, 10(6), 589; https://doi.org/10.3390/ma10060589 - 27 May 2017

Cited by 14 | Viewed by 4268

Abstract

The breakage of capsules upon crack propagation is crucial for achieving crack healing in encapsulation-based self-healing materials. A mesomechanical model was developed in this study to simulate the process of crack propagation in a matrix and the potential of debonding. The model used [...] Read more.

The breakage of capsules upon crack propagation is crucial for achieving crack healing in encapsulation-based self-healing materials. A mesomechanical model was developed in this study to simulate the process of crack propagation in a matrix and the potential of debonding. The model used the extended finite element method (XFEM) combined with a cohesive zone model (CZM) in a two-dimensional (2D) configuration. The configuration consisted of an infinite matrix with an embedded crack and a capsule nearby, all subjected to a uniaxial remote tensile load. A parametric study was performed to investigate the effect of geometry, elastic parameters and fracture properties on the fracture response of the system. The results indicated that the effect of the capsule wall on the fracture behavior of the matrix is insignificant for t_c/R_c ≤ 0.05. The matrix strength influenced the ultimate crack length, while the Young’s modulus ratio E_c/E_m only affected the rate of crack propagation. The potential for capsule breakage or debonding was dependent on the comparative strength between capsule and interface (S_c/S_int), provided the crack could reach the capsule. The critical value of S_c_,cr/S_int,crwas obtained using this model for materials design. Full article

(This article belongs to the Special Issue Modeling and Simulation of Advanced Composite Materials)

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Open AccessArticle

Cytotoxicity Evaluation of High-Temperature Annealed Nanohydroxyapatite in Contact with Fibroblast Cells

by Maria Szymonowicz, Mariusz Korczynski, Maciej Dobrzynski, Katarzyna Zawisza, Marcin Mikulewicz, Ewa Karuga-Kuzniewska, Boguslawa Zywickab, Zbigniew Rybak and Rafal J. Wiglusz

Materials 2017, 10(6), 590; https://doi.org/10.3390/ma10060590 - 27 May 2017

Cited by 23 | Viewed by 4112

Abstract

Biomaterials are substances manufactured for medical purposes in direct contact with the tissues of organisms. Prior to their use, they are tested to determine their usefulness and safety of application. Hydroxyapatites are used in medicine as a bony complement because of their similarity [...] Read more.

Biomaterials are substances manufactured for medical purposes in direct contact with the tissues of organisms. Prior to their use, they are tested to determine their usefulness and safety of application. Hydroxyapatites are used in medicine as a bony complement because of their similarity to the natural apatite therein. Thanks to their bioactivity, biocompatibility, stability and non-toxicity hydroxyapatite are the most commonly used materials in osteoimplantology. The use of materials at the nanoscale in medicine or biology may carry the risk of undesirable effects. The aim of the study was to evaluate the cytotoxic effect of high-temperature annealed nanohydroxyapatites on the L929 murine fibroblasts. Nanohydroxyapatites in powder form were obtained by the wet chemistry method: in the temperature range of 800–1000 °C and used for the study. Based on performed studies evaluating the morphology and fibroblast viability, it was found that nanohydroxyapatites show no cytotoxic effects on the L929 cell line. Full article

(This article belongs to the Section Biomaterials)

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2876 KiB

Open AccessArticle

Ultrathin Six-Band Polarization-Insensitive Perfect Metamaterial Absorber Based on a Cross-Cave Patch Resonator for Terahertz Waves

by Yong Zhi Cheng, Mu Lin Huang, Hao Ran Chen, Zhen Zhong Guo, Xue Song Mao and Rong Zhou Gong

Materials 2017, 10(6), 591; https://doi.org/10.3390/ma10060591 - 28 May 2017

Cited by 89 | Viewed by 6364

Abstract

A simple design of an ultrathin six-band polarization-insensitive terahertz perfect metamaterial absorber (PMMA), composed of a metal cross-cave patch resonator (CCPR) placed over a ground plane, was proposed and investigated numerically. The numerical simulation results demonstrate that the average absorption peaks are up [...] Read more.

A simple design of an ultrathin six-band polarization-insensitive terahertz perfect metamaterial absorber (PMMA), composed of a metal cross-cave patch resonator (CCPR) placed over a ground plane, was proposed and investigated numerically. The numerical simulation results demonstrate that the average absorption peaks are up to 95% at six resonance frequencies. Owing to the ultra-narrow band resonance absorption of the structure, the designed PMMA also exhibits a higher Q factor (>65). In addition, the absorption properties can be kept stable for both normal incident transverse magnetic (TM) and transverse electric (TE) waves. The physical mechanism behind the observed high-level absorption is illustrated by the electric and power loss density distributions. The perfect absorption originates mainly from the higher-order multipolar plasmon resonance of the structure, which differs sharply from most previous studies of PMMAs. Furthermore, the resonance absorption properties of the PMMA can be modified and adjusted easily by varying the geometric parameters of the unit cell. Full article

(This article belongs to the Section Advanced Materials Characterization)

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Open AccessArticle

The Effects of Relative Humidity on the Flowability and Dispersion Performance of Lactose Mixtures

by Xiang-Yun Lu, Lan Chen, Chuan-Yu Wu, Hak-Kim Chan and Tim Freeman

Materials 2017, 10(6), 592; https://doi.org/10.3390/ma10060592 - 29 May 2017

Cited by 31 | Viewed by 5276

Abstract

The flowability and dispersion behavior are two important physicochemical properties of pharmaceutical formulations for dry powder inhalers (DPIs). They are usually affected by the environmental conditions, such as temperature and relative humidity (RH). However, very few studies have been focused on the relationship [...] Read more.

The flowability and dispersion behavior are two important physicochemical properties of pharmaceutical formulations for dry powder inhalers (DPIs). They are usually affected by the environmental conditions, such as temperature and relative humidity (RH). However, very few studies have been focused on the relationship between the two properties and their dependence on RH during storage. In this research, model pharmaceutical formulations were prepared using mixtures of coarse and fine lactose. The fractions of fines in the mixtures were 0%, 5%, 10%, and 20%, respectively. These blends were stored at four different RH levels, 0%, 30%, 58%, and 85%, for 48 h. The FT4 Powder Rheometer was used to evaluate the powder flowability, and the Malvern Spraytec^® laser diffraction system was employed to assess the powder dispersion performance. The results indicated that both the flow and dispersion properties of lactose blends deteriorate after being stored at 85% RH, but improved after being conditioned at 58% RH. The fine particle fractions (FPFs) of the blends with 5% and 10% fine fractions and the as-received coarse lactose decreased when they were conditioned at 30% RH. For the blend with 20% fine fraction, a high RH during storage (i.e., 85% RH) affected the dispersion property, but had a limited influence on its flowability, while, for the coarse lactose powder, the different RH conditions affected its flowability, but not the dispersion results. A strong correlation between the powder flowability and its dispersion performance was found. Full article

(This article belongs to the Special Issue Materials for Drug Delivery and Biomedical Consideration)

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4737 KiB

Open AccessArticle

Neutron Diffraction Evaluation of Near Surface Residual Stresses at Welds in 1300 MPa Yield Strength Steel

by Ebrahim Harati, Leif Karlsson, Lars-Erik Svensson, Thilo Pirling and Kamellia Dalaei

Materials 2017, 10(6), 593; https://doi.org/10.3390/ma10060593 - 29 May 2017

Cited by 12 | Viewed by 4604

Abstract

Evaluation of residual stress in the weld toe region is of critical importance. In this paper, the residual stress distribution both near the surface and in depth around the weld toe was investigated using neutron diffraction, complemented with X-ray diffraction. Measurements were done [...] Read more.

Evaluation of residual stress in the weld toe region is of critical importance. In this paper, the residual stress distribution both near the surface and in depth around the weld toe was investigated using neutron diffraction, complemented with X-ray diffraction. Measurements were done on a 1300 MPa yield strength steel welded using a Low Transformation Temperature (LTT) consumable. Near surface residual stresses, as close as 39 µm below the surface, were measured using neutron diffraction and evaluated by applying a near surface data correction technique. Very steep surface stress gradients within 0.5 mm of the surface were found both at the weld toe and 2 mm into the heat affected zone (HAZ). Neutron results showed that the LTT consumable was capable of inducing near surface compressive residual stresses in all directions at the weld toe. It is concluded that there are very steep stress gradients both transverse to the weld toe line and in the depth direction, at the weld toe in LTT welds. Residual stress in the base material a few millimeters from the weld toe can be very different from the stress at the weld toe. Care must, therefore, be exercised when relating the residual stress to fatigue strength in LTT welds. Full article

(This article belongs to the Section Advanced Materials Characterization)

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Open AccessArticle

Rapid Prototyping of Slot Die Devices for Roll to Roll Production of EL Fibers

by Alyssa Bellingham, Nicholas Bromhead and Adam Fontecchio

Materials 2017, 10(6), 594; https://doi.org/10.3390/ma10060594 - 29 May 2017

Cited by 13 | Viewed by 3620

Abstract

There is a growing interest in fibers supporting optoelectrical properties for textile and wearable display applications. Solution-processed electroluminescent (EL) material systems can be continuously deposited onto fiber or yarn substrates in a roll-to-roll process, making it easy to scale manufacturing. It is important [...] Read more.

There is a growing interest in fibers supporting optoelectrical properties for textile and wearable display applications. Solution-processed electroluminescent (EL) material systems can be continuously deposited onto fiber or yarn substrates in a roll-to-roll process, making it easy to scale manufacturing. It is important to have precise control over layer deposition to achieve uniform and reliable light emission from these EL fibers. Slot-die coating offers this control and increases the rate of EL fiber production. Here, we report a highly adaptable, cost-effective 3D printing model for developing slot dies used in automatic coating systems. The resulting slot-die coating system enables rapid, reliable production of alternating current powder-based EL (ACPEL) fibers and can be adapted for many material systems. The benefits of this system over dip-coating for roll-to-roll production of EL fibers are demonstrated in this work. Full article

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Open AccessArticle

Characterization of a Laser Surface-Treated Martensitic Stainless Steel

by S.R. Al-Sayed, A.A. Hussein, A.A. Nofal, S.I. Hassab Elnaby and H. Elgazzar

Materials 2017, 10(6), 595; https://doi.org/10.3390/ma10060595 - 29 May 2017

Cited by 36 | Viewed by 8545

Abstract

Laser surface treatment was carried out on AISI 416 machinable martensitic stainless steel containing 0.225 wt.% sulfur. Nd:YAG laser with a 2.2-KW continuous wave was used. The aim was to compare the physical and chemical properties achieved by this type of selective surface [...] Read more.

Laser surface treatment was carried out on AISI 416 machinable martensitic stainless steel containing 0.225 wt.% sulfur. Nd:YAG laser with a 2.2-KW continuous wave was used. The aim was to compare the physical and chemical properties achieved by this type of selective surface treatment with those achieved by the conventional treatment. Laser power of different values (700 and 1000 W) with four corresponding different laser scanning speeds (0.5, 1, 2, and 3 m•min−1) was adopted to reach the optimum conditions for impact toughness, wear, and corrosion resistance for laser heat treated (LHT) samples. The 0 °C impact energy of LHT samples indicated higher values compared to the conventionally heat treated (CHT) samples. This was accompanied by the formation of a hard surface layer and a soft interior base metal. Microhardness was studied to determine the variation of hardness values with respect to the depth under the treated surface. The wear resistance at the surface was enhanced considerably. Microstructure examination was characterized using optical and scanning electron microscopes. The corrosion behavior of the LHT samples was also studied and its correlation with the microstructures was determined. The corrosion data was obtained in 3.5% NaCl solution at room temperature by means of a potentiodynamic polarization technique. Full article

(This article belongs to the Special Issue Laser in Nanotechnology and Biomedical Applications)

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Open AccessArticle

Synthesis, Characterization and Hexavalent Chromium Adsorption Characteristics of Aluminum- and Sucrose-Incorporated Tobermorite

by Zhiguang Zhao, Jiangxiong Wei, Fangxian Li, Xiaoling Qu, Liang Shi, Haidong Zhang and Qijun Yu

Materials 2017, 10(6), 597; https://doi.org/10.3390/ma10060597 - 30 May 2017

Cited by 24 | Viewed by 5898

Abstract

Tobermorites were synthesized from the lime-quartz slurries with incorporations of aluminum and sucrose under hydrothermal conditions, and then used for adsorption of Cr(VI). The chemical components, and structural and morphological properties of tobermorite were characterized by X-ray diffraction (XRD), thermogravimetric-differential scanning calorimetry (TG-DSC), [...] Read more.

Tobermorites were synthesized from the lime-quartz slurries with incorporations of aluminum and sucrose under hydrothermal conditions, and then used for adsorption of Cr(VI). The chemical components, and structural and morphological properties of tobermorite were characterized by X-ray diffraction (XRD), thermogravimetric-differential scanning calorimetry (TG-DSC), Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), X-ray photoelectron spectroscopic (XPS) and N₂ adsorption–desorption measurements. The formation and crystallinity of tobermorite could be largely enhanced by adding 2.3 wt.% aluminum hydroxide or 13.3 wt.% sucrose. Sucrose also played a significantly positive role in increasing the surface area. The adsorption performances for Cr(VI) were tested using a batch method taking into account the effects of pH, the adsorption kinetics, and the adsorption isotherms. The adsorption capacities of the aluminum- and sucrose-incorporated tobermorites reached up to 31.65 mg/g and 28.92 mg/g, respectively. Thus, the synthesized tobermorites showed good adsorption properties for removal of Cr(VI), making this material a promising candidate for efficient bulk wastewater treatment. Full article

(This article belongs to the Special Issue Sorption Materials for Environment Purification)

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Open AccessArticle

Long-Term Behaviour of Fly Ash and Slag Cement Grouts for Micropiles Exposed to a Sulphate Aggressive Medium

by José Marcos Ortega, María Dolores Esteban, Raúl Rubén Rodríguez, José Luis Pastor, Francisco José Ibanco, Isidro Sánchez and Miguel Ángel Climent

Materials 2017, 10(6), 598; https://doi.org/10.3390/ma10060598 - 30 May 2017

Cited by 38 | Viewed by 3887

Abstract

Nowadays, one of the most popular ways to get a more sustainable cement industry is using additions as cement replacement. However, there are many civil engineering applications in which the use of sustainable cements is not extended yet, such as special foundations, and [...] Read more.

Nowadays, one of the most popular ways to get a more sustainable cement industry is using additions as cement replacement. However, there are many civil engineering applications in which the use of sustainable cements is not extended yet, such as special foundations, and particularly micropiles, even though the standards do not restrict the cement type to use. These elements are frequently exposed to the sulphates present in soils. The purpose of this research is to study the effects in the very long-term (until 600 days) of sulphate attack in the microstructure of micropiles grouts, prepared with ordinary Portland cement, fly ash and slag commercial cements, continuing a previous work, in which these effects were studied in the short-term. The microstructure changes have been analysed with the non-destructive impedance spectroscopy technique, mercury intrusion porosimetry and the “Wenner” resistivity test. The mass variation and the compressive strength have also been studied. The impedance spectroscopy has been the most sensitive technique for following the sulphate attack process. Considering the results obtained, micropiles grouts with slag and fly ash, exposed to an aggressive medium with high content of sulphates, have shown good behaviour in the very long-term (600 days) compared to grouts made with OPC. Full article

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Open AccessArticle

Theoretical Investigations of Si-Ge Alloys in P4₂/ncm Phase: First-Principles Calculations

by Zhenyang Ma, Xuhong Liu, Xinhai Yu, Chunlei Shi and Fang Yan

Materials 2017, 10(6), 599; https://doi.org/10.3390/ma10060599 - 31 May 2017

Cited by 14 | Viewed by 5037

Abstract

The structural, mechanical, anisotropic, electronic and thermal properties of Si, Si_0.667Ge_0.333, Si_0.333Ge_0.667 and Ge in P4₂/ncm phase are investigated in this work. The calculations have been performed with an ultra-soft pseudopotential by [...] Read more.

The structural, mechanical, anisotropic, electronic and thermal properties of Si, Si_0.667Ge_0.333, Si_0.333Ge_0.667 and Ge in P4₂/ncm phase are investigated in this work. The calculations have been performed with an ultra-soft pseudopotential by using the generalized gradient approximation and local density approximation in the framework of density functional theory. The achieved results for the lattice constants and band gaps of P4₂/ncm-Si and P4₂/ncm-Ge in this research have good accordance with other results. The calculated elastic constants and elastic moduli of the Si, Si_0.667Ge_0.333, Si_0.333Ge_0.667 and Ge in P4₂/ncm phase are better than that of the Si, Si_0.667Ge_0.333, Si_0.333Ge_0.667 and Ge in P4₂/mnm phase. The Si, Si_0.667Ge_0.333, Si_0.333Ge_0.667 and Ge in P4₂/ncm phase exhibit varying degrees of mechanical anisotropic properties in Poisson’s ratio, shear modulus, Young’s modulus, and universal anisotropic index. The band structures of the Si, Si_0.667Ge_0.333, Si_0.333Ge_0.667 and Ge in P4₂/ncm phase show that they are all indirect band gap semiconductors with band gap of 1.46 eV, 1.25 eV, 1.36 eV and 1.00 eV, respectively. In addition, we also found that the minimum thermal conductivity κ_min of the Si, Si_0.667Ge_0.333, Si_0.333Ge_0.667 and Ge in P4₂/ncm phase exhibit different degrees of anisotropic properties in (001), (010), (100) and (

0 \bar{1} 0

) planes. Full article

(This article belongs to the Section Advanced Materials Characterization)

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Open AccessArticle

Structural, Morphological, Optical and Photocatalytic Properties of Y, N-Doped and Codoped TiO₂ Thin Films

by Zeineb Hamden, David Conceição, Sami Boufi, Luís Filipe Vieira Ferreira and Soraa Bouattour

Materials 2017, 10(6), 600; https://doi.org/10.3390/ma10060600 - 31 May 2017

Cited by 9 | Viewed by 4529

Abstract

Pure TiO₂, Y-N single-doped and codoped TiO₂ powders and thin films deposited on glass beads were successfully prepared using dip-coating and sol-gel methods. The samples were analyzed using grazing angle X-ray diffraction (GXRD), Raman spectroscopy, time resolved luminescence, ground state [...] Read more.

Pure TiO₂, Y-N single-doped and codoped TiO₂ powders and thin films deposited on glass beads were successfully prepared using dip-coating and sol-gel methods. The samples were analyzed using grazing angle X-ray diffraction (GXRD), Raman spectroscopy, time resolved luminescence, ground state diffuse reflectance absorption and scanning electron microscopy (SEM). According to the GXRD patterns and micro-Raman spectra, only the anatase form of TiO₂ was made evident. Ground state diffuse reflectance absorption studies showed that doping with N or codoping with N and Y led to an increase of the band gap. Laser induced luminescence analysis revealed a decrease in the recombination rate of the photogenerated holes and electrons. The photocatalytic activity of supported catalysts, toward the degradation of toluidine, revealed a meaningful enhancement upon codoping samples at a level of 2% (atomic ratio). The photocatalytic activity of the material and its reactivity can be attributed to a reduced, but significant, direct photoexcitation of the semiconductor by the halogen lamp, together with a charge-transfer-complex mechanism, or with the formation of surface oxygen vacancies by the N dopant atoms. Full article

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Open AccessArticle

Annual Atmospheric Corrosion of Carbon Steel Worldwide. An Integration of ISOCORRAG, ICP/UNECE and MICAT Databases

by Belén Chico, Daniel De la Fuente, Iván Díaz, Joaquín Simancas and Manuel Morcillo

Materials 2017, 10(6), 601; https://doi.org/10.3390/ma10060601 - 31 May 2017

Cited by 61 | Viewed by 6484

Abstract

In the 1980s, three ambitious international programmes on atmospheric corrosion (ISOCORRAG, ICP/UNECE and MICAT), involving the participation of a total of 38 countries on four continents, Europe, America, Asia and Oceania, were launched. Though each programme has its own particular characteristics, the similarity [...] Read more.

In the 1980s, three ambitious international programmes on atmospheric corrosion (ISOCORRAG, ICP/UNECE and MICAT), involving the participation of a total of 38 countries on four continents, Europe, America, Asia and Oceania, were launched. Though each programme has its own particular characteristics, the similarity of the basic methodologies used makes it possible to integrate the databases obtained in each case. This paper addresses such an integration with the aim of establishing simple universal damage functions (DF) between first year carbon steel corrosion in the different atmospheres and available environmental variables, both meteorological (temperature (T), relative humidity (RH), precipitation (P), and time of wetness (TOW)) and pollution (SO₂ and NaCl). In the statistical processing of the data, it has been chosen to differentiate between marine atmospheres and those in which the chloride deposition rate is insignificant (<3 mg/m².d). In the DF established for non-marine atmospheres a great influence of the SO₂ content in the atmosphere was seen, as well as lesser effects by the meteorological parameters of RH and T. Both NaCl and SO₂ pollutants, in that order, are seen to be the most influential variables in marine atmospheres, along with a smaller impact of TOW. Full article

(This article belongs to the Special Issue Fundamental and Research Frontier of Atmospheric Corrosion)

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Open AccessArticle

Rapid and Sensitive Detection of Bacteria Response to Antibiotics Using Nanoporous Membrane and Graphene Quantum Dot (GQDs)-Based Electrochemical Biosensors

by Weiwei Ye, Jiubiao Guo, Xianfeng Bao, Tian Chen, Wenchuan Weng, Sheng Chen and Mo Yang

Materials 2017, 10(6), 603; https://doi.org/10.3390/ma10060603 - 31 May 2017

Cited by 33 | Viewed by 6299

Abstract

The wide abuse of antibiotics has accelerated bacterial multiresistance, which means there is a need to develop tools for rapid detection and characterization of bacterial response to antibiotics in the management of infections. In the study, an electrochemical biosensor based on nanoporous alumina [...] Read more.

The wide abuse of antibiotics has accelerated bacterial multiresistance, which means there is a need to develop tools for rapid detection and characterization of bacterial response to antibiotics in the management of infections. In the study, an electrochemical biosensor based on nanoporous alumina membrane and graphene quantum dots (GQDs) was developed for bacterial response to antibiotics detection. Anti-Salmonella antibody was conjugated with amino-modified GQDs by glutaraldehyde and immobilized on silanized nanoporous alumina membranes for Salmonella bacteria capture. The impedance signals across nanoporous membranes could monitor the capture of bacteria on nanoporous membranes as well as bacterial response to antibiotics. This nanoporous membrane and GQD-based electrochemical biosensor achieved rapid detection of bacterial response to antibiotics within 30 min, and the detection limit could reach the pM level. It was capable of investigating the response of bacteria exposed to antibiotics much more rapidly and conveniently than traditional tools. The capability of studying the dynamic effects of antibiotics on bacteria has potential applications in the field of monitoring disease therapy, detecting comprehensive food safety hazards and even life in hostile environment. Full article

(This article belongs to the Special Issue Bioapplications of Graphene Composites)

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Open AccessArticle

Solid-State Method Synthesis of SnO₂-Decorated g-C₃N₄ Nanocomposites with Enhanced Gas-Sensing Property to Ethanol

by Jianliang Cao, Cong Qin, Yan Wang, Huoli Zhang, Guang Sun and Zhanying Zhang

Materials 2017, 10(6), 604; https://doi.org/10.3390/ma10060604 - 31 May 2017

Cited by 103 | Viewed by 8251

Abstract

SnO₂/graphitic carbon nitride (g-C₃N₄) composites were synthesized via a facile solid-state method by using SnCl₄·5H₂O and urea as the precursor. The structure and morphology of the as-synthesized composites were characterized by the techniques [...] Read more.

SnO₂/graphitic carbon nitride (g-C₃N₄) composites were synthesized via a facile solid-state method by using SnCl₄·5H₂O and urea as the precursor. The structure and morphology of the as-synthesized composites were characterized by the techniques of X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), thermogravimetry-differential thermal analysis (TG-DTA), X-ray photoelectron spectroscopy (XPS), and N₂ sorption. The results indicated that the composites possessed a two-dimensional (2-D) structure, and the SnO₂ nanoparticles were highly dispersed on the surface of the g-C₃N₄ nanosheets. The gas-sensing performance of the samples to ethanol was tested, and the SnO₂/g-C₃N₄ nanocomposite-based sensor exhibited admirable properties. The response value (Ra/Rg) of the SnO₂/g-C₃N₄ nanocomposite with 10 wt % 2-D g-C₃N₄ content-based sensor to 500 ppm of ethanol was 550 at 300 °C. However, the response value of pure SnO₂ was only 320. The high surface area of SnO₂/g-C₃N₄-10 (140 m²·g⁻¹) and the interaction between 2-D g-C₃N₄ and SnO₂ could strongly affect the gas-sensing property. Full article

(This article belongs to the Special Issue Ultrathin Two-dimensional (2D) Nanomaterials)

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5030 KiB

Open AccessArticle

Reduction of Defects in AlGaN Grown on Nanoscale-Patterned Sapphire Substrates by Hydride Vapor Phase Epitaxy

by Chi-Tsung Tasi, Wei-Kai Wang, Tsung-Yen Tsai, Shih-Yung Huang, Ray-Hua Horng and Dong-Sing Wuu

Materials 2017, 10(6), 605; https://doi.org/10.3390/ma10060605 - 31 May 2017

Cited by 5 | Viewed by 4674

Abstract

In this study, a 3-μm-thick AlGaN film with an Al mole fraction of 10% was grown on a nanoscale-patterned sapphire substrate (NPSS) using hydride vapor phase epitaxy (HVPE). The growth mechanism, crystallization, and surface morphology of the epilayers were examined using X-ray diffraction, [...] Read more.

In this study, a 3-μm-thick AlGaN film with an Al mole fraction of 10% was grown on a nanoscale-patterned sapphire substrate (NPSS) using hydride vapor phase epitaxy (HVPE). The growth mechanism, crystallization, and surface morphology of the epilayers were examined using X-ray diffraction, transmission electron microscopy (TEM), and scanning electron microscopy at various times in the growth process. The screw threading dislocation (TD) density of AlGaN-on-NPSS can improve to 1–2 × 10⁹ cm⁻², which is significantly lower than that of the sample grown on a conventional planar sapphire substrate (7 × 10⁹ cm⁻²). TEM analysis indicated that these TDs do not subsequently propagate to the surface of the overgrown AlGaN layer, but bend or change directions in the region above the voids within the side faces of the patterned substrates, possibly because of the internal stress-relaxed morphologies of the AlGaN film. Hence, the laterally overgrown AlGaN films were obtained by HVPE, which can serve as a template for the growth of ultraviolet III-nitride optoelectronic devices. Full article

(This article belongs to the Section Manufacturing Processes and Systems)

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Open AccessArticle

Graphene Nanosheets to Improve Physico-Mechanical Properties of Bioactive Calcium Silicate Cements

by Nileshkumar Dubey, Sneha Sundar Rajan, Yuri Dal Bello, Kyung-San Min and Vinicius Rosa

Materials 2017, 10(6), 606; https://doi.org/10.3390/ma10060606 - 31 May 2017

Cited by 50 | Viewed by 5435

Abstract

Bioactive calcium silicate cements are widely used to induce mineralization, to cement prosthetic parts, in the management of tooth perforations, and other areas. Nonetheless, they can present clinical disadvantages, such as long setting time and modest physico-mechanical properties. The objective of this work [...] Read more.

Bioactive calcium silicate cements are widely used to induce mineralization, to cement prosthetic parts, in the management of tooth perforations, and other areas. Nonetheless, they can present clinical disadvantages, such as long setting time and modest physico-mechanical properties. The objective of this work was to evaluate the potential of graphene nanosheets (GNS) to improve two bioactive cements. GNS were obtained via reduction of graphite oxide. GNS were mixed (1, 3, 5, and 7 wt %) with Biodentine (BIO) and Endocem Zr (ECZ), and the effects on setting time, hardness, push-out strength, pH profile, cell proliferation, and mineralization were evaluated. Statistics were performed with two-way ANOVA and Tukey test (α = 0.05). GNS has not interfered in the composition of the set cements as confirmed by Raman, FT-IR and XRD. GNS (1 and 3 wt %) shortened the setting time, increased hardness of both materials but decreased significantly the push-out strength of ECZ. pH was not affected but 1 wt % and 7 wt % to ECZ and 5 wt % to BIO increased the mineralization compared to the controls. In summary, GNS may be an alternative to improve the physico-mechanical properties and bioactivity of cements. Nonetheless, the use of GNS may not be advised for all materials when effective bonding is a concern. Full article

(This article belongs to the Special Issue Bioapplications of Graphene Composites)

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Open AccessArticle

Optical Absorption Enhancement in CdTe Thin Films by Microstructuration of the Silicon Substrate

by Jesús Rangel-Cárdenas and Hugo Sobral

Materials 2017, 10(6), 607; https://doi.org/10.3390/ma10060607 - 1 Jun 2017

Cited by 47 | Viewed by 5379

Abstract

In this work, the reflectance, optical absorption, and band gap have been determined for CdTe thin films grown on planar and microstructured substrates. The treated surface was prepared by laser ablation of a silicon wafer, forming holes in a periodic arrangement. Thin films [...] Read more.

In this work, the reflectance, optical absorption, and band gap have been determined for CdTe thin films grown on planar and microstructured substrates. The treated surface was prepared by laser ablation of a silicon wafer, forming holes in a periodic arrangement. Thin films were grown by pulsed laser ablation on silicon samples kept at 200 °C inside a vacuum chamber. The presence of CdTe was verified with X-ray diffraction and Raman spectroscopy indicating a nanocrystalline zinc blended structure. The optical absorption of thin films was calculated by using the Fresnel laws and the experimental reflectance spectrum. Results show that reflectance of 245 nm films deposited on modified substrates is reduced by up to a factor of two than the obtained on unchanged silicon and the optical absorption is 16% higher at ~456 nm. Additionally, it was determined that the band gap energy for planar and microstructured films is about 1.44 eV for both cases. Full article

(This article belongs to the Section Advanced Materials Characterization)

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Open AccessArticle

Co₃O₄@CoS Core-Shell Nanosheets on Carbon Cloth for High Performance Supercapacitor Electrodes

by Jinfeng Ning, Tianyu Zhang, Ying He, Congpu Jia, Petr Saha and Qilin Cheng

Materials 2017, 10(6), 608; https://doi.org/10.3390/ma10060608 - 1 Jun 2017

Cited by 53 | Viewed by 8571

Abstract

In this work, a two-step electrodeposition strategy is developed for the synthesis of core-shell Co₃O₄@CoS nanosheet arrays on carbon cloth (CC) for supercapacitor applications. Porous Co₃O₄ nanosheet arrays are first directly grown on CC by electrodeposition, [...] Read more.

In this work, a two-step electrodeposition strategy is developed for the synthesis of core-shell Co₃O₄@CoS nanosheet arrays on carbon cloth (CC) for supercapacitor applications. Porous Co₃O₄ nanosheet arrays are first directly grown on CC by electrodeposition, followed by the coating of a thin layer of CoS on the surface of Co₃O₄ nanosheets via the secondary electrodeposition. The morphology control of the ternary composites can be easily achieved by altering the number of cyclic voltammetry (CV) cycles of CoS deposition. Electrochemical performance of the composite electrodes was evaluated by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy techniques. The results demonstrate that the Co₃O₄@CoS/CC with 4 CV cycles of CoS deposition possesses the largest specific capacitance 887.5 F·g⁻¹ at a scan rate of 10 mV·s⁻¹(764.2 F·g⁻¹ at a current density of 1.0 A·g⁻¹), and excellent cycling stability (78.1% capacitance retention) at high current density of 5.0 A·g⁻¹ after 5000 cycles. The porous nanostructures on CC not only provide large accessible surface area for fast ions diffusion, electron transport and efficient utilization of active CoS and Co₃O₄, but also reduce the internal resistance of electrodes, which leads to superior electrochemical performance of Co₃O₄@CoS/CC composite at 4 cycles of CoS deposition. Full article

(This article belongs to the Section Energy Materials)

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Open AccessArticle

Microarc Oxidation Coating Combined with Surface Pore-Sealing Treatment Enhances Corrosion Fatigue Performance of 7075-T7351 Al Alloy in Different Media

by Hui-Hui Yang, Xi-Shu Wang, Ya-Ming Wang, Yan-Ling Wang and Zhi-Hao Zhang

Materials 2017, 10(6), 609; https://doi.org/10.3390/ma10060609 - 2 Jun 2017

Cited by 27 | Viewed by 5000

Abstract

Rotating bending fatigue tests have been performed to evaluate the corrosion fatigue performance and its influence factors of 7075-T7351 Al alloy in different media, namely air and a 5.0 wt % NaCl aqueous solution. All samples were coated by microarc oxidation (MAO) coating [...] Read more.

Rotating bending fatigue tests have been performed to evaluate the corrosion fatigue performance and its influence factors of 7075-T7351 Al alloy in different media, namely air and a 5.0 wt % NaCl aqueous solution. All samples were coated by microarc oxidation (MAO) coating technology; some samples were followed by an epoxy resin pore-sealing treatment. Microscopic analyses of the surfaces and fracture cross-sections of samples were carried out. The results reveal that the sample with a MAO coating of 10 μm thickness and pore-sealing treatment by epoxy resin possesses optimal corrosion fatigue performance in the different media. The MAO coating with a pore-sealing treatment significantly improves the corrosion fatigue limit of 7075-T7351 Al alloy. Full article

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Open AccessArticle

The Preparation of Porous Sol-Gel Silica with Metal Organic Framework MIL-101(Cr) by Microwave-Assisted Hydrothermal Method for Adsorption Chillers

by Kasimayan Uma, Guan-Ting Pan and Thomas C-K. Yang

Materials 2017, 10(6), 610; https://doi.org/10.3390/ma10060610 - 2 Jun 2017

Cited by 20 | Viewed by 6395

Abstract

Abstract: Metal organic framework (MOF) of MIL-101(Cr)-Silica (SiO₂) composites with highly mesoporous and uniform dispersions were synthesized by a microwave-assisted hydrothermal method followed by the sol-gel technique. Water vapor adsorption experiments were conducted on the MIL-101(Cr)-SiO₂ composites for [...] Read more.

Abstract: Metal organic framework (MOF) of MIL-101(Cr)-Silica (SiO₂) composites with highly mesoporous and uniform dispersions were synthesized by a microwave-assisted hydrothermal method followed by the sol-gel technique. Water vapor adsorption experiments were conducted on the MIL-101(Cr)-SiO₂ composites for industrial adsorption chiller applications. The effects of MIL-101(Cr)-SiO₂ mixing ratios (ranging from 0% to 52%), the surface area and amount of Lewis and Brønsted sites were comprehensively determined through water vapor adsorption experiments and the adsorption mechanism is also explained. The BET and Langmuir results indicate that the adsorption isotherms associated with the various MIL-101(Cr)-SiO₂ ratios demonstrated Type I and IV adsorption behavior, due to the mesoporous structure of the MIL-101(Cr)-SiO₂. It was observed that the increase in the amount of Lewis and Brønsted sites on the MIL-101(Cr)-SiO₂ composites significantly improves the water vapor adsorption efficiency, for greater stability during the water vapor adsorption experiments. Full article

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Open AccessArticle

Fabrication Method Study of ZnO Nanocoated Cellulose Film and Its Piezoelectric Property

by Hyun-U Ko, Hyun Chan Kim, Jung Woong Kim, Lindong Zhai and Jaehwan Kim

Materials 2017, 10(6), 611; https://doi.org/10.3390/ma10060611 - 2 Jun 2017

Cited by 13 | Viewed by 3992

Abstract

Recently, a cellulose-based composite material with a thin ZnO nanolayer—namely, ZnO nanocoated cellulose film (ZONCE)—was fabricated to increase its piezoelectric charge constant. However, the fabrication method has limitations to its application in mass production. In this paper, a hydrothermal synthesis method suitable for [...] Read more.

Recently, a cellulose-based composite material with a thin ZnO nanolayer—namely, ZnO nanocoated cellulose film (ZONCE)—was fabricated to increase its piezoelectric charge constant. However, the fabrication method has limitations to its application in mass production. In this paper, a hydrothermal synthesis method suitable for the mass production of ZONCE (HZONCE) is proposed. A simple hydrothermal synthesis which includes a hydrothermal reaction is used for the production, and the reaction time is controlled. To improve the piezoelectric charge constant, the hydrothermal reaction is conducted twice. HZONCE fabricated by twice-hydrothermal reaction shows approximately 1.6-times improved piezoelectric charge constant compared to HZONCE fabricated by single hydrothermal reaction. Since the fabricated HZONCE has high transparency, dielectric constant, and piezoelectric constant, the proposed method can be applied for continuous mass production. Full article

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Open AccessCommunication

Frequency-Stable Ionic-Type Hybrid Gate Dielectrics for High Mobility Solution-Processed Metal-Oxide Thin-Film Transistors

by Jae Sang Heo, Seungbeom Choi, Jeong-Wan Jo, Jingu Kang, Ho-Hyun Park, Yong-Hoon Kim and Sung Kyu Park

Materials 2017, 10(6), 612; https://doi.org/10.3390/ma10060612 - 3 Jun 2017

Cited by 9 | Viewed by 5426

Abstract

In this paper, we demonstrate high mobility solution-processed metal-oxide thin-film transistors (TFTs) by using a high-frequency-stable ionic-type hybrid gate dielectric (HGD). The HGD gate dielectric, a blend of sol-gel aluminum oxide (AlO_x) and poly(4-vinylphenol) (PVP), exhibited high dielectric constant (ε~8.15) and [...] Read more.

In this paper, we demonstrate high mobility solution-processed metal-oxide thin-film transistors (TFTs) by using a high-frequency-stable ionic-type hybrid gate dielectric (HGD). The HGD gate dielectric, a blend of sol-gel aluminum oxide (AlO_x) and poly(4-vinylphenol) (PVP), exhibited high dielectric constant (ε~8.15) and high-frequency-stable characteristics (1 MHz). Using the ionic-type HGD as a gate dielectric layer, an minimal electron-double-layer (EDL) can be formed at the gate dielectric/InO_x interface, enhancing the field-effect mobility of the TFTs. Particularly, using the ionic-type HGD gate dielectrics annealed at 350 °C, InO_x TFTs having an average field-effect mobility of 16.1 cm²/Vs were achieved (maximum mobility of 24 cm²/Vs). Furthermore, the ionic-type HGD gate dielectrics can be processed at a low temperature of 150 °C, which may enable their applications in low-thermal-budget plastic and elastomeric substrates. In addition, we systematically studied the operational stability of the InO_x TFTs using the HGD gate dielectric, and it was observed that the HGD gate dielectric effectively suppressed the negative threshold voltage shift during the negative-illumination-bias stress possibly owing to the recombination of hole carriers injected in the gate dielectric with the negatively charged ionic species in the HGD gate dielectric. Full article

(This article belongs to the Special Issue Oxide Semiconductor Thin-Film Transistor)

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Open AccessArticle

Hydrogen-Induced Delayed Cracking in TRIP-Aided Lean-Alloyed Ferritic-Austenitic Stainless Steels

by Suvi Papula, Teemu Sarikka, Severi Anttila, Juho Talonen, Iikka Virkkunen and Hannu Hänninen

Materials 2017, 10(6), 613; https://doi.org/10.3390/ma10060613 - 3 Jun 2017

Cited by 4 | Viewed by 4616

Abstract

Susceptibility of three lean-alloyed ferritic-austenitic stainless steels to hydrogen-induced delayed cracking was examined, concentrating on internal hydrogen contained in the materials after production operations. The aim was to study the role of strain-induced austenite to martensite transformation in the delayed cracking susceptibility. According [...] Read more.

Susceptibility of three lean-alloyed ferritic-austenitic stainless steels to hydrogen-induced delayed cracking was examined, concentrating on internal hydrogen contained in the materials after production operations. The aim was to study the role of strain-induced austenite to martensite transformation in the delayed cracking susceptibility. According to the conducted deep drawing tests and constant load tensile testing, the studied materials seem not to be particularly susceptible to delayed cracking. Delayed cracks were only occasionally initiated in two of the materials at high local stress levels. However, if a delayed crack initiated in a highly stressed location, strain-induced martensite transformation decreased the crack arrest tendency of the austenite phase in a duplex microstructure. According to electron microscopy examination and electron backscattering diffraction analysis, the fracture mode was predominantly cleavage, and cracks propagated along the body-centered cubic (BCC) phases ferrite and α’-martensite. The BCC crystal structure enables fast diffusion of hydrogen to the crack tip area. No delayed cracking was observed in the stainless steel that had high austenite stability. Thus, it can be concluded that the presence of α’-martensite increases the hydrogen-induced cracking susceptibility. Full article

(This article belongs to the Section Advanced Materials Characterization)

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Open AccessArticle

Performance of a New Al₂O₃/Ce–TZP Ceramic Nanocomposite Dental Implant: A Pilot Study in Dogs.

by Roberto Lopez-Píriz, Adolfo Fernández, Lidia Goyos-Ball, Sergio Rivera, Luis A. Díaz, Manuel Fernández-Domínguez, Catuxa Prado, José S. Moya and Ramón Torrecillas

Materials 2017, 10(6), 614; https://doi.org/10.3390/ma10060614 - 3 Jun 2017

Cited by 24 | Viewed by 5987

Abstract

Although titanium remains as the prevalent material in dental implant manufacturing new zirconia-based materials that overcome the major drawbacks of the standard 3Y–yttria partially-stabilized zirconia (Y-TZP) are now emerging. In this study, a new ceramic nanocomposite made of alumina and ceria-stabilized TZP (ZCe-A) [...] Read more.

Although titanium remains as the prevalent material in dental implant manufacturing new zirconia-based materials that overcome the major drawbacks of the standard 3Y–yttria partially-stabilized zirconia (Y-TZP) are now emerging. In this study, a new ceramic nanocomposite made of alumina and ceria-stabilized TZP (ZCe-A) has been used to produce dental implants with the mechanic and topographic characteristics of a pilot implant design to evaluate bone and soft tissue integration in a dog model (n = 5). Histological cross-section analysis of the implanted ceramic fixations (n = 15) showed not only perfect biocompatibility, but also a high rate of osseous integration (defined as the percentage of bone to implant contact) and soft tissue attachment. This clinical success, in combination with the superior mechanical properties achieved by this Al₂O₃/Ce-TZP nanocomposite, may place this material as an improved alternative of traditional 3Y-TZP dental implants. Full article

(This article belongs to the Special Issue Dental Implant Materials)

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Open AccessArticle

Development of Viscoelastic Multi-Body Simulation and Impact Response Analysis of a Ballasted Railway Track under Cyclic Loading

by Daisuke Nishiura, Hide Sakaguchi and Akira Aikawa

Materials 2017, 10(6), 615; https://doi.org/10.3390/ma10060615 - 3 Jun 2017

Cited by 11 | Viewed by 6238

Abstract

Simulation of a large number of deformable bodies is often difficult because complex high-level modeling is required to address both multi-body contact and viscoelastic deformation. This necessitates the combined use of a discrete element method (DEM) and a finite element method (FEM). In [...] Read more.

Simulation of a large number of deformable bodies is often difficult because complex high-level modeling is required to address both multi-body contact and viscoelastic deformation. This necessitates the combined use of a discrete element method (DEM) and a finite element method (FEM). In this study, a quadruple discrete element method (QDEM) was developed for dynamic analysis of viscoelastic materials using a simpler algorithm compared to the standard FEM. QDEM easily incorporates the contact algorithm used in DEM. As the first step toward multi-body simulation, the fundamental performance of QDEM was investigated for viscoelastic analysis. The amplitude and frequency of cantilever elastic vibration were nearly equal to those obtained by the standard FEM. A comparison of creep recovery tests with an analytical solution showed good agreement between them. In addition, good correlation between the attenuation degree and the real physical viscosity was confirmed for viscoelastic vibration analysis. Therefore, the high accuracy of QDEM in the fundamental analysis of infinitesimal viscoelastic deformations was verified. Finally, the impact response of a ballast and sleeper under cyclic loading on a railway track was analyzed using QDEM as an application of deformable multi-body dynamics. The results showed that the vibration of the ballasted track was qualitatively in good agreement with the actual measurements. Moreover, the ballast layer with high friction reduced the ballasted track deterioration. This study suggests that QDEM, as an alternative to DEM and FEM, can provide deeper insights into the contact dynamics of a large number of deformable bodies. Full article

(This article belongs to the Special Issue Computational Mechanics of Cohesive-Frictional Materials)

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Open AccessArticle

Non-Destructive Inspection of Impact Damage in Composite Aircraft Panels by Ultrasonic Guided Waves and Statistical Processing

by Margherita Capriotti, Hyungsuk E. Kim, Francesco Lanza di Scalea and Hyonny Kim

Materials 2017, 10(6), 616; https://doi.org/10.3390/ma10060616 - 4 Jun 2017

Cited by 35 | Viewed by 6111

Abstract

This paper discusses a non-destructive evaluation (NDE) technique for the detection of damage in composite aircraft structures following high energy wide area blunt impact (HEWABI) from ground service equipment (GSE), such as heavy cargo loaders and other heavy equipment. The test structures typically [...] Read more.

This paper discusses a non-destructive evaluation (NDE) technique for the detection of damage in composite aircraft structures following high energy wide area blunt impact (HEWABI) from ground service equipment (GSE), such as heavy cargo loaders and other heavy equipment. The test structures typically include skin, co-cured stringers, and C-frames that are bolt-connected onto the skin with shear ties. The inspection exploits the waveguide geometry of these structures by utilizing ultrasonic guided waves and a line scan approach. Both a contact prototype and a non-contact prototype were developed and tested on realistic test panels subjected to impact in the laboratory. The results are presented in terms of receiver operating characteristic curves that show excellent probability of detection with low false alarm rates for defects located in the panel skin and stringers. Full article

(This article belongs to the Special Issue Structural Health Monitoring for Aerospace Applications 2017)

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Open AccessArticle

Thermal Stability of P-Type BiSbTe Alloys Prepared by Melt Spinning and Rapid Sintering

by Yun Zheng, Gangjian Tan, Yubo Luo, Xianli Su, Yonggao Yan and Xinfeng Tang

Materials 2017, 10(6), 617; https://doi.org/10.3390/ma10060617 - 6 Jun 2017

Cited by 20 | Viewed by 5005

Abstract

P-type BiSbTe alloys have been widely implemented in waste heat recovery from low-grade heat sources below 600 K, which may involve assorted environments and conditions, such as long-term service, high-temperature exposure (generally 473–573 K) and mechanical forces. It is important to evaluate the [...] Read more.

P-type BiSbTe alloys have been widely implemented in waste heat recovery from low-grade heat sources below 600 K, which may involve assorted environments and conditions, such as long-term service, high-temperature exposure (generally 473–573 K) and mechanical forces. It is important to evaluate the service performance of these materials in order to prevent possible failures in advance and extend the life cycle. In this study, p-type Bi_0.5Sb_1.5Te₃ commercial zone-melting (ZM) ingots were processed by melt spinning and subsequent plasma-activated sintering (MS-PAS), and were then subjected to vacuum-annealing at 473 and 573 K, respectively, for one week. The results show that MS-PAS samples exhibit excellent thermal stability when annealed at 473 K. However, thermal annealing at 573 K for MS-PAS specimens leads to the distinct sublimation of the element Te, which degrades the hole concentration remarkably and results in inferior thermoelectric performance. Furthermore, MS-PAS samples annealed at 473 K demonstrate a slight enhancement in flexural and compressive strengths, probably due to the reduction of residual stress induced during the sintering process. The current work guides the reliable application of p-type Bi_0.5Sb_1.5Te₃ compounds prepared by the MS-PAS technique. Full article

(This article belongs to the Special Issue Advance in Plasmonics and Metamaterials)

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Open AccessFeature PaperArticle

Mechanical Properties of Nonwoven Reinforced Thermoplastic Polyurethane Composites

by Muhammad Tausif, Achilles Pliakas, Tom O’Haire, Parikshit Goswami and Stephen J. Russell

Materials 2017, 10(6), 618; https://doi.org/10.3390/ma10060618 - 5 Jun 2017

Cited by 12 | Viewed by 6772

Abstract

Reinforcement of flexible fibre reinforced plastic (FRP) composites with standard textile fibres is a potential low cost solution to less critical loading applications. The mechanical behaviour of FRPs based on mechanically bonded nonwoven preforms composed of either low or high modulus fibres in [...] Read more.

Reinforcement of flexible fibre reinforced plastic (FRP) composites with standard textile fibres is a potential low cost solution to less critical loading applications. The mechanical behaviour of FRPs based on mechanically bonded nonwoven preforms composed of either low or high modulus fibres in a thermoplastic polyurethane (TPU) matrix were compared following compression moulding. Nonwoven preform fibre compositions were selected from lyocell, polyethylene terephthalate (PET), polyamide (PA) as well as para-aramid fibres (polyphenylene terephthalamide; PPTA). Reinforcement with standard fibres manifold improved the tensile modulus and strength of the reinforced composites and the relationship between fibre, fabric and composite’s mechanical properties was studied. The linear density of fibres and the punch density, a key process variable used to consolidate the nonwoven preform, were varied to study the influence on resulting FRP mechanical properties. In summary, increasing the strength and degree of consolidation of nonwoven preforms did not translate to an increase in the strength of resulting fibre reinforced TPU-composites. The TPU composite strength was mainly dependent upon constituent fibre stress-strain behaviour and fibre segment orientation distribution. Full article

(This article belongs to the Special Issue Textile Composites)

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Open AccessArticle

Cellulose Fibre-Reinforced Biofoam for Structural Applications

by Jasmina Obradovic, Mikko Voutilainen, Pasi Virtanen, Lippo Lassila and Pedro Fardim

Materials 2017, 10(6), 619; https://doi.org/10.3390/ma10060619 - 6 Jun 2017

Cited by 20 | Viewed by 6643

Abstract

Traditionally, polymers and macromolecular components used in the foam industry are mostly derived from petroleum. The current transition to a bio-economy creates demand for the use of more renewable feedstocks. Soybean oil is a vegetable oil, composed mainly of triglycerides, that is suitable [...] Read more.

Traditionally, polymers and macromolecular components used in the foam industry are mostly derived from petroleum. The current transition to a bio-economy creates demand for the use of more renewable feedstocks. Soybean oil is a vegetable oil, composed mainly of triglycerides, that is suitable material for foam production. In this study, acrylated epoxidized soybean oil and variable amounts of cellulose fibres were used in the production of bio-based foam. The developed macroporous bio-based architectures were characterised by several techniques, including porosity measurements, nanoindentation testing, scanning electron microscopy, and thermogravimetric analysis. It was found that the introduction of cellulose fibres during the foaming process was necessary to create the three-dimensional polymer foams. Using cellulose fibres has potential as a foam stabiliser because it obstructs the drainage of liquid from the film region in these gas-oil interfaces while simultaneously acting as a reinforcing agent in the polymer foam. The resulting foams possessed a porosity of approximately 56%, and the incorporation of cellulose fibres did not affect thermal behaviour. Scanning electron micrographs showed randomly oriented pores with irregular shapes and non-uniform pore size throughout the samples. Full article

(This article belongs to the Section Biomaterials)

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Open AccessFeature PaperArticle

Experimental Modeling of a Formula Student Carbon Composite Nose Cone

by Neil A. Fellows

Materials 2017, 10(6), 620; https://doi.org/10.3390/ma10060620 - 6 Jun 2017

Cited by 2 | Viewed by 7774

Abstract

A numerical impact study is presented on a Formula Student (FS) racing car carbon composite nose cone. The effect of material model and model parameter selection on the numerical deceleration curves is discussed in light of the experimental deceleration data. The models show [...] Read more.

A numerical impact study is presented on a Formula Student (FS) racing car carbon composite nose cone. The effect of material model and model parameter selection on the numerical deceleration curves is discussed in light of the experimental deceleration data. The models show reasonable correlation in terms of the shape of the deceleration-displacement curves but do not match the peak deceleration values with errors greater that 30%. Full article

(This article belongs to the Special Issue Materials in Motorsport)

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Open AccessArticle

Using B₄C Nanoparticles to Enhance Thermal and Mechanical Response of Aluminum

by Fareeha Ubaid, Penchal Reddy Matli, Rana Abdul Shakoor, Gururaj Parande, Vyasaraj Manakari, Adel Mohamed Amer Mohamed and Manoj Gupta

Materials 2017, 10(6), 621; https://doi.org/10.3390/ma10060621 - 6 Jun 2017

Cited by 36 | Viewed by 4590

Abstract

In this work, Al-B₄C nanocomposites were produced by microwave sintering and followed by hot extrusion processes. The influence of ceramic reinforcement (B₄C) nanoparticles on the physical, microstructural, mechanical, and thermal characteristics of the extruded Al-B₄C nanocomposites was [...] Read more.

In this work, Al-B₄C nanocomposites were produced by microwave sintering and followed by hot extrusion processes. The influence of ceramic reinforcement (B₄C) nanoparticles on the physical, microstructural, mechanical, and thermal characteristics of the extruded Al-B₄C nanocomposites was investigated. It was observed that the density decreased and porosity increased with an increase in B₄C content in aluminum matrix. The porosity of the composites increased whereas density decreased with increasing B₄C content. Electron microscopy analysis reveals the uniform distribution of B4C nanoparticles in the Al matrix. Mechanical characterization results revealed that hardness, elastic modulus, compression, and tensile strengths increased whereas ductility decreases with increasing B₄C content. Al-1.0 vol. % B₄C nanocomposite exhibited best hardness (135.56 Hv), Young’s modulus (88.63 GPa), and compression/tensile strength (524.67/194.41 MPa) among the materials investigated. Further, coefficient of thermal expansion (CTE) of composites gradually decreased with an increase in B₄C content. Full article

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Open AccessArticle

Sparse and Dispersion-Based Matching Pursuit for Minimizing the Dispersion Effect Occurring when Using Guided Wave for Pipe Inspection

by Javad Rostami, Peter W.T Tse and Zhou Fang

Materials 2017, 10(6), 622; https://doi.org/10.3390/ma10060622 - 6 Jun 2017

Cited by 32 | Viewed by 4601

Abstract

Ultrasonic guided wave is an effective tool for structural health monitoring of structures for detecting defects. In practice, guided wave signals are dispersive and contain multiple modes and noise. In the presence of overlapped wave-packets/modes and noise together with dispersion, extracting meaningful information [...] Read more.

Ultrasonic guided wave is an effective tool for structural health monitoring of structures for detecting defects. In practice, guided wave signals are dispersive and contain multiple modes and noise. In the presence of overlapped wave-packets/modes and noise together with dispersion, extracting meaningful information from these signals is a challenging task. Handling such challenge requires an advanced signal processing tool. The aim of this study is to develop an effective and robust signal processing tool to deal with the complexity of guided wave signals for non-destructive testing (NDT) purpose. To achieve this goal, Sparse Representation with Dispersion Based Matching Pursuit (SDMP) is proposed. Addressing the three abovementioned facts that complicate signal interpretation, SDMP separates overlapped modes and demonstrates good performance against noise with maximum sparsity. With the dispersion taken into account, an overc-omplete and redundant dictionary of basic atoms based on a narrowband excitation signal is designed. As Finite Element Method (FEM) was used to predict the form of wave packets propagating along structures, these atoms have the maximum resemblance with real guided wave signals. SDMP operates in two stages. In the first stage, similar to Matching Pursuit (MP), the approximation improves by adding, a single atom to the solution set at each iteration. However, atom selection criterion of SDMP utilizes the time localization of guided wave reflections that makes a portion of overlapped wave-packets to be composed mainly of a single echo. In the second stage of the algorithm, the selected atoms that have frequency inconsistency with the excitation signal are discarded. This increases the sparsity of the final representation. Meanwhile, leading to accurate approximation, as discarded atoms are not representing guided wave reflections, it simplifies extracting physical meanings for defect detection purpose. To verify the effectiveness of SDMP for damage detection results from numerical simulations and experiments on steel pipes are presented. Full article

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Open AccessArticle

Comparison of Two Xenograft Materials Used in Sinus Lift Procedures: Material Characterization and In Vivo Behavior

by María Piedad Ramírez Fernández, Patricia Mazón, Sergio A. Gehrke, Jose Luis Calvo-Guirado and Piedad N. De Aza

Materials 2017, 10(6), 623; https://doi.org/10.3390/ma10060623 - 7 Jun 2017

Cited by 22 | Viewed by 6735

Abstract

Detailed information about graft material characteristic is crucial to evaluate their clinical outcomes. The present study evaluates the physico-chemical characteristics of two xenografts manufactured on an industrial scale deproteinized at different temperatures (non-sintered and sintered) in accordance with a protocol previously used in [...] Read more.

Detailed information about graft material characteristic is crucial to evaluate their clinical outcomes. The present study evaluates the physico-chemical characteristics of two xenografts manufactured on an industrial scale deproteinized at different temperatures (non-sintered and sintered) in accordance with a protocol previously used in sinus lift procedures. It compares how the physico-chemical properties influence the material’s performance in vivo by a histomorphometric study in retrieved bone biopsies following maxillary sinus augmentation in 10 clinical cases. An X-ray diffraction analysis revealed the typical structure of hydroxyapatite (HA) for both materials. Both xenografts were porous and exhibited intraparticle pores. Strong differences were observed in terms of porosity, crystallinity, and calcium/phosphate. Histomorphometric measurements on the bone biopsies showed statistically significant differences. The physic-chemical assessment of both xenografts, made in accordance with the protocol developed on an industrial scale, confirmed that these products present excellent biocompatibilitity, with similar characteristics to natural bone. The sintered HA xenografts exhibited greater osteoconductivity, but were not completely resorbable (30.80 ± 0.88% residual material). The non-sintered HA xenografts induced about 25.92 ± 1.61% of new bone and a high level of degradation after six months of implantation. Differences in the physico-chemical characteristics found between the two HA xenografts determined a different behavior for this material. Full article

(This article belongs to the Special Issue Biocompatibility of Materials)

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Open AccessArticle

Fracture Surface Morphology and Impact Strength of Cellulose/PLA Composites

by Honghong Gao and Tao Qiang

Materials 2017, 10(6), 624; https://doi.org/10.3390/ma10060624 - 7 Jun 2017

Cited by 50 | Viewed by 8698

Abstract

Polylactide (PLA)-based composite materials reinforced with ball-milled celluloses were manufactured by extrusion blending followed by injection molding. Their surface morphology from impact fracture were imaged with scanning electron microscopy (SEM) and investigated by calculating their fractal dimensions. Then, linear regression was used to [...] Read more.

Polylactide (PLA)-based composite materials reinforced with ball-milled celluloses were manufactured by extrusion blending followed by injection molding. Their surface morphology from impact fracture were imaged with scanning electron microscopy (SEM) and investigated by calculating their fractal dimensions. Then, linear regression was used to explore the relationship between fractal dimension and impact strength of the resultant cellulose/PLA composite materials. The results show that filling the ball-milled celluloses into PLA can improve the impact toughness of PLA by a minimum of 38%. It was demonstrated that the fracture pattern of the cellulose/PLA composite materials is different from that of pristine PLA. For the resultant composite materials, the fractal dimension of the impact fractured surfaces increased with increasing filling content and decreasing particle size of the ball-milled cellulose particles. There were highly positive correlations between fractal dimension of the fractured surfaces and impact strength of the cellulose/PLA composites. However, the linearity between fractal dimension and impact strength were different for the different methods, due to their different R-squared values. The approach presented in this work will help to understand the structure–property relationships of composite materials from a new perspective. Full article

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Open AccessArticle

A Study of Structure and Magnetic Properties of Low Purity Fe-Co-Based Metallic Glasses

by Sabina Lesz

Materials 2017, 10(6), 625; https://doi.org/10.3390/ma10060625 - 8 Jun 2017

Cited by 6 | Viewed by 3945

Abstract

This paper is related to the evaluation of the possibility of using ferroalloys for the production of conventional (CMGs) and bulk metallic glasses (BMGs) as well as determining their magnetic properties. The structure and magnetic properties of Fe-Co-based CMGs and BMGs prepared from [...] Read more.

This paper is related to the evaluation of the possibility of using ferroalloys for the production of conventional (CMGs) and bulk metallic glasses (BMGs) as well as determining their magnetic properties. The structure and magnetic properties of Fe-Co-based CMGs and BMGs prepared from ferroalloys and pure elements, were studied. The CMGs and BMGs were in the form of ribbons and rods, respectively. The thickness of the ribbons were 0.07, 0.12, and 0.27 mm and the diameters of the rods were 1.5 and 2.5 mm. The investigations of the structure of the test specimens were carried out using the X-ray diffraction (XRD) method and electron microscopy methods (HRTEM—high-resolution transmission electron microscope, SEM—scanning electron microscope). The relationship between the structure and magnetic properties of the Fe_36.00Co_36.00B_19.00Si₅Nb₄ and Fe_35.75Co_35.75B_18.90Si₅Nb₄Cu_0.6 CMGs and BMGs was determined. The possibility of using new materials, i.e., CMGs and BMGs, prepared on the basis of ferroalloys, lies in the scope of the presently conducted research and allows us to obtain the utility properties, while avoiding high costs associated with the purchase of raw materials. Full article

(This article belongs to the Section Advanced Materials Characterization)

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Open AccessCommunication

Structure-Controllable Synthesis of Multiferroic YFeO₃ Nanopowders and Their Optical and Magnetic Properties

by Meng Wang, Ting Wang, Shenhua Song and Manlin Tan

Materials 2017, 10(6), 626; https://doi.org/10.3390/ma10060626 - 7 Jun 2017

Cited by 24 | Viewed by 4139

Abstract

Phase-pure hexagonal and orthorhombic YFeO₃ nanopowders are synthesized by low-temperature solid-state reaction along with Zr doping. The obtained powders are characterized by X-ray diffraction, field emission scanning electron microscopy, and physical property measurements. The hexagonal YFeO₃ exhibits a narrower optical band [...] Read more.

Phase-pure hexagonal and orthorhombic YFeO₃ nanopowders are synthesized by low-temperature solid-state reaction along with Zr doping. The obtained powders are characterized by X-ray diffraction, field emission scanning electron microscopy, and physical property measurements. The hexagonal YFeO₃ exhibits a narrower optical band gap in comparison to the orthorhombic one, while the orthorhombic YFeO₃ presents better magnetic properties. The formation of hexagonal or orthorhombic phase can be effectively controlled by Zr doping. The temperature range of synthesizing the hexagonal YFeO₃ nanopowders is increased by ~200 °C due to Zr doping so that they can be easily synthesized, which possesses a finer particle size and a smaller optical band gap, making it favorable for optical applications. Full article

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Open AccessArticle

Effect of the SiCl₄ Flow Rate on SiBN Deposition Kinetics in SiCl₄-BCl₃-NH₃-H₂-Ar Environment

by Jianping Li, Hailong Qin, Yongsheng Liu, Fang Ye, Zan Li, Laifei Cheng and Litong Zhang

Materials 2017, 10(6), 627; https://doi.org/10.3390/ma10060627 - 7 Jun 2017

Cited by 7 | Viewed by 4082

Abstract

To improve the thermal and mechanical stability of SiC_f/SiC or C/SiC composites with SiBN interphase, SiBN coating was deposited by low pressure chemical vapor deposition (LPCVD) using SiCl₄-BCl₃-NH₃-H₂-Ar gas system. The effect of [...] Read more.

To improve the thermal and mechanical stability of SiC_f/SiC or C/SiC composites with SiBN interphase, SiBN coating was deposited by low pressure chemical vapor deposition (LPCVD) using SiCl₄-BCl₃-NH₃-H₂-Ar gas system. The effect of the SiCl₄ flow rate on deposition kinetics was investigated. Results show that deposition rate increases at first and then decreases with the increase of the SiCl₄ flow rate. The surface of the coating is a uniform cauliflower-like structure at the SiCl₄ flow rate of 10 mL/min and 20 mL/min. The surface is covered with small spherical particles when the flow rate is 30 mL/min. The coatings deposited at various SiCl₄ flow rates are all X-ray amorphous and contain Si, B, N, and O elements. The main bonding states are B-N, Si-N, and N-O. B element and B-N bonding decrease with the increase of SiCl₄ flow rate, while Si element and Si-N bonding increase. The main deposition mechanism refers to two parallel reactions of BCl₃+NH₃ and SiCl₄+NH₃. The deposition process is mainly controlled by the reaction of BCl₃+NH₃. Full article

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Open AccessArticle

Preparation of Superhydrophobic Film on Ti Substrate and Its Anticorrosion Property

by Min Zhu, Wenchuan Tang, Luyao Huang, Dawei Zhang, Cuiwei Du, Gaohong Yu, Ming Chen and Thee Chowwanonthapunya

Materials 2017, 10(6), 628; https://doi.org/10.3390/ma10060628 - 8 Jun 2017

Cited by 21 | Viewed by 4270

Abstract

Superhydrophobic films were fabricated on a titanium substrate with or without anodizing by using a self-assembling method. Firstly, the pretreatments of mechanical polishing/anodizing or mechanical polishing only were conducted, respectively. Subsequently, the preparation of polydopamine film layer, deposition of nano-silver particles, and post [...] Read more.

Superhydrophobic films were fabricated on a titanium substrate with or without anodizing by using a self-assembling method. Firstly, the pretreatments of mechanical polishing/anodizing or mechanical polishing only were conducted, respectively. Subsequently, the preparation of polydopamine film layer, deposition of nano-silver particles, and post modification of 1H,1H,2H,2H-perfluorodecanethiol were performed on the surface of the pretreated substrate. The surface morphologies, compositions, wettability, and corrosion resistance of the films were investigated with scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), water contact angle measurements, and electrochemical tests, respectively. Meanwhile, the effect of the deposition time in the silver nitrate solution on the hydrophobicity of the specimen surface was investigated. The result showed that with the increase of deposition time, the hydrophobic property enhanced gradually. The surface deposited for 7 h exhibited an optimum hydrophobic effect, which was characterized with a large water contact angle (WCA) of 154°, and the surface was rather rough and covered by a relatively uniform layer of micro-nano silver particles. The excellent hydrophobicity was attributed to a rough stratified microstructure along with the low surface energy. The electrochemical measurements showed that the existence of the superhydrophobic film can effectively enhance the corrosion resistance of Ti samples. Full article

(This article belongs to the Section Biomaterials)

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Open AccessArticle

Effects of Strand Lay Direction and Crossing Angle on Tribological Behavior of Winding Hoist Rope

by Xiang-dong Chang, Yu-xing Peng, Zhen-cai Zhu, Xian-sheng Gong, Zhang-fa Yu, Zhen-tao Mi and Chun-ming Xu

Materials 2017, 10(6), 630; https://doi.org/10.3390/ma10060630 - 9 Jun 2017

Cited by 29 | Viewed by 5849

Abstract

Friction and wear behavior exists between hoisting ropes that are wound around the drums of a multi-layer winding hoist. It decreases the service life of ropes and threatens mine safety. In this research, a series of experiments were conducted using a self-made test [...] Read more.

Friction and wear behavior exists between hoisting ropes that are wound around the drums of a multi-layer winding hoist. It decreases the service life of ropes and threatens mine safety. In this research, a series of experiments were conducted using a self-made test rig to study the effects of the strand lay direction and crossing angle on the winding rope’s tribological behavior. Results show that the friction coefficient in the steady-state period shows a decreasing tendency with an increase of the crossing angle in both cross directions, but the variation range is different under different cross directions. Using thermal imaging, the high temperature regions always distribute along the strand lay direction in the gap between adjacent strands, as the cross direction is the same with the strand lay direction (right cross contact). Additionally, the temperature rise in the steady-state increases with the increase of the crossing angle in both cross directions. The differences of the wear scar morphology are obvious under different cross directions, especially for the large crossing angle tests. In the case of right cross, the variation range of wear mass loss is larger than that in left cross. The damage that forms on the wear surface is mainly ploughing, pits, plastic deformation, and fatigue fracture. The major wear mechanisms are adhesive wear, and abrasive and fatigue wear. Full article

(This article belongs to the Special Issue Tribological Behavior of Materials by Surface Engineering)

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Open AccessArticle

Structure and Photocatalytic Properties of Mn-Doped TiO₂ Loaded on Wood-Based Activated Carbon Fiber Composites

by Xiaojun Ma, Wanru Zhou and Yin Chen

Materials 2017, 10(6), 631; https://doi.org/10.3390/ma10060631 - 9 Jun 2017

Cited by 40 | Viewed by 5899

Abstract

Mn-doped TiO₂ loaded on wood-based activated carbon fiber (Mn/TiO₂-WACF) was prepared by sol–gel and impregnation method using MnSO₄·H₂O as manganese source. The structure of Mn/TiO₂–WACF was characterized by SEM, XRD, FTIR, N₂ adsorption [...] Read more.

Mn-doped TiO₂ loaded on wood-based activated carbon fiber (Mn/TiO₂-WACF) was prepared by sol–gel and impregnation method using MnSO₄·H₂O as manganese source. The structure of Mn/TiO₂–WACF was characterized by SEM, XRD, FTIR, N₂ adsorption and UV–Vis, and its photocatalytic activity for methylene blue degradation was investigated. Results show that Mn-doped TiO₂ were loaded on the surface of wood-based activated carbon fiber with high-development pore structures. The crystallite sizes of Mn-doped TiO₂ in composites were smaller than that of the undoped samples. With an increase of Mn doping content, Ti–O bending vibration intensity of Mn/TiO₂–WACF increased and then decreased. Moreover, Ti–O–Ti and Ti–O–Mn absorption peaks increased upon doping of Mn. Mn/TiO₂–WACF with low specific surface area, and pore volume was improved at 3.5–6.0 nm of mesopore distributions due to the Mn-doped TiO₂ load. In addition, the UV–Vis showed that Mn/TiO₂–WACF (photodegradation rate of 96%) has higher photocatalytic activity than the undoped samples for methylene blue degradation under visible light irradiation. Full article

(This article belongs to the Special Issue Enhancing the Photocatalytic Activity of TiO2 Photocatalysts)

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Open AccessArticle

Stability of an Electrodeposited Nanocrystalline Ni-Based Alloy Coating in Oil and Gas Wells with the Coexistence of H₂S and CO₂

by Yiyong Sui, Chong Sun, Jianbo Sun, Baolin Pu, Wei Ren and Weimin Zhao

Materials 2017, 10(6), 632; https://doi.org/10.3390/ma10060632 - 9 Jun 2017

Cited by 13 | Viewed by 4028

Abstract

The stability of an electrodeposited nanocrystalline Ni-based alloy coating in a H₂S/CO₂ environment was investigated by electrochemical measurements, weight loss method, and surface characterization. The results showed that both the cathodic and anodic processes of the Ni-based alloy coating were [...] Read more.

The stability of an electrodeposited nanocrystalline Ni-based alloy coating in a H₂S/CO₂ environment was investigated by electrochemical measurements, weight loss method, and surface characterization. The results showed that both the cathodic and anodic processes of the Ni-based alloy coating were simultaneously suppressed, displaying a dramatic decrease of the corrosion current density. The corrosion of the Ni-based alloy coating was controlled by H₂S corrosion and showed general corrosion morphology under the test temperatures. The corrosion products, mainly consisting of Ni₃S₂, NiS, or Ni₃S₄, had excellent stability in acid solution. The corrosion rate decreased with the rise of temperature, while the adhesive force of the corrosion scale increased. With the rise of temperature, the deposited morphology and composition of corrosion products changed, the NiS content in the corrosion scale increased, and the stability and adhesive strength of the corrosion scale improved. The corrosion scale of the Ni-based alloy coating was stable, compact, had strong adhesion, and caused low weight loss, so the corrosion rates calculated by the weight loss method cannot reveal the actual oxidation rate of the coating. As the corrosion time was prolonged, the Ni-based coating was thinned while the corrosion scale thickened. The corrosion scale was closely combined with the coating, but cannot fully prevent the corrosive reactants from reaching the substrate. Full article

(This article belongs to the Special Issue Corrosion Studies of Metal Matrix Composites/Alloys at Low and High Temperatures)

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Open AccessArticle

Influence of Discharge Current on Phase Transition Properties of High Quality Polycrystalline VO₂ Thin Film Fabricated by HiPIMS

by Tiegui Lin, Jian Wang, Gang Liu, Langping Wang, Xiaofeng Wang and Yufen Zhang

Materials 2017, 10(6), 633; https://doi.org/10.3390/ma10060633 - 9 Jun 2017

Cited by 9 | Viewed by 4974

Abstract

To fabricate high-quality polycrystalline VO₂ thin film with a metal–insulator transition (MIT) temperature less than 50 °C, high-power impulse magnetron sputtering with different discharge currents was employed in this study. The as-deposited VO₂ films were characterized by a four-point probe resistivity [...] Read more.

To fabricate high-quality polycrystalline VO₂ thin film with a metal–insulator transition (MIT) temperature less than 50 °C, high-power impulse magnetron sputtering with different discharge currents was employed in this study. The as-deposited VO₂ films were characterized by a four-point probe resistivity measurement system, visible-near infrared (IR) transmittance spectra, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy. The resistivity results revealed that all the as-deposited films had a high resistance change in the phase transition process, and the MIT temperature decreased with the increased discharge current, where little deterioration in the phase transition properties, such as the resistance and transmittance changes, could be found. Additionally, XRD patterns at various temperatures exhibited that some reverse deformations that existed in the MIT process of the VO₂ film, with a large amount of preferred crystalline orientations. The decrease of the MIT temperature with little deterioration on phase transition properties could be attributed to the reduction of the preferred grain orientations. Full article

(This article belongs to the Special Issue Metal-Insulator Transition)

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Open AccessArticle

Extractant Immobilization in Alginate Capsules (Matrix- and Mononuclear-Type): Application to Pb(II) Sorption from HCl Solutions

by Janette Alba, Ricardo Navarro, Imelda Saucedo, Thierry Vincent and Eric Guibal

Materials 2017, 10(6), 634; https://doi.org/10.3390/ma10060634 - 9 Jun 2017

Cited by 2 | Viewed by 4197

Abstract

The decontamination of dilute industrial effluents is a critical challenge for decreasing the environmental impact of mining and metallurgical activities. As an alternative to conventional processes, new extractant impregnated resins (EIRs) have been synthesized by the immobilization of Cyanex 301 and Cyanex 302 [...] Read more.

The decontamination of dilute industrial effluents is a critical challenge for decreasing the environmental impact of mining and metallurgical activities. As an alternative to conventional processes, new extractant impregnated resins (EIRs) have been synthesized by the immobilization of Cyanex 301 and Cyanex 302 in alginate capsules using two different procedures (matrix-type immobilization vs. mononuclear encapsulation). These materials have been tested for Pb(II) sorption from acidic solutions. The Langmuir equation fitted well the sorption isotherms and the maximum sorption capacities vary between 24 and 80 mg·g⁻¹ at pH 1, depending on the type and loading of the extractant in the EIR. Uptake kinetics were controlled by the resistance to intraparticle diffusion; though both the Crank equation (intraparticle diffusion) and pseudo-second order rate equation equally fitted uptake profiles. The amount of extractant immobilized in mononuclear capsules is lower than in matrix-type beads; this leads to lower sorption capacities but slightly better mass transfer properties. The balance between the advantages and drawbacks of the different systems makes more promising matrix-type capsules. The desorption of Pb(II) is possible using 1 M HNO₃ solutions: metal ions were completely desorbed. However, the probable oxidation of the extractants (conversion to oxidized forms more sensitive to pH) reduces the sorption efficiency when they are re-used. Full article

(This article belongs to the Special Issue Sorption Materials for Environment Purification)

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Open AccessArticle

The Use of Empirical Methods for Testing Granular Materials in Analogue Modelling

by Domenico Montanari, Andrea Agostini, Marco Bonini, Giacomo Corti and Chiara Del Ventisette

Materials 2017, 10(6), 635; https://doi.org/10.3390/ma10060635 - 9 Jun 2017

Cited by 43 | Viewed by 7070

Abstract

The behaviour of a granular material is mainly dependent on its frictional properties, angle of internal friction, and cohesion, which, together with material density, are the key factors to be considered during the scaling procedure of analogue models. The frictional properties of a [...] Read more.

The behaviour of a granular material is mainly dependent on its frictional properties, angle of internal friction, and cohesion, which, together with material density, are the key factors to be considered during the scaling procedure of analogue models. The frictional properties of a granular material are usually investigated by means of technical instruments such as a Hubbert-type apparatus and ring shear testers, which allow for investigating the response of the tested material to a wide range of applied stresses. Here we explore the possibility to determine material properties by means of different empirical methods applied to mixtures of quartz and K-feldspar sand. Empirical methods exhibit the great advantage of measuring the properties of a certain analogue material under the experimental conditions, which are strongly sensitive to the handling techniques. Finally, the results obtained from the empirical methods have been compared with ring shear tests carried out on the same materials, which show a satisfactory agreement with those determined empirically. Full article

(This article belongs to the Special Issue Granular Materials)

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Open AccessFeature PaperArticle

Recovery of Silver Using Adsorption Gels Prepared from Microalgal Residue Immobilized with Functional Groups Containing Sulfur or Nitrogen

by Kanjana Khunathai, Katsutoshi Inoue, Keisuke Ohto, Hidetaka Kawakita, Minoru Kurata, Kinya Atsumi, Hiroaki Fukuda and Shafiq Alam

Materials 2017, 10(6), 636; https://doi.org/10.3390/ma10060636 - 10 Jun 2017

Cited by 11 | Viewed by 3929

Abstract

Although biodiesel oil extracted from microalgae attracts much attention as one of the most promising green energies, its high production cost is a big problem, impeding its extensive use. In order to lower the production cost, the effective use of microalgal residue after [...] Read more.

Although biodiesel oil extracted from microalgae attracts much attention as one of the most promising green energies, its high production cost is a big problem, impeding its extensive use. In order to lower the production cost, the effective use of microalgal residue after extracting biofuel was investigated as a feed material of functional materials. In the present work, a new adsorbent for silver(I) was prepared by immobilizing functional groups of polyethylene-polyamine or dithiooxamide, which exhibita high affinity for soft Lewis acids such as silver(I) ions. Their adsorption behaviors for silver(I) were investigated from aqueous nitrate and acidothiourea media. The effects of the concentrations of nitrate and thiourea, as well as of sulfuric acid, were qualitatively interpreted. From the study of adsorption isotherms on these gels, they were found to exhibita higher adsorption capacity than the majority of those reported to date. Full article

(This article belongs to the Special Issue Sorption Materials for Environment Purification)

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Open AccessArticle

Analysis of the Light Transmission Ability of Reinforcing Glass Fibers Used in Polymer Composites

by Gergely Hegedűs, Tamás Sarkadi and Tibor Czigány

Materials 2017, 10(6), 637; https://doi.org/10.3390/ma10060637 - 10 Jun 2017

Cited by 20 | Viewed by 4171

Abstract

This goal of our research was to show that E-glass fiber bundles used for reinforcing composites can be enabled to transmit light in a common resin without any special preparation (without removing the sizing). The power of the transmitted light was measured and [...] Read more.

This goal of our research was to show that E-glass fiber bundles used for reinforcing composites can be enabled to transmit light in a common resin without any special preparation (without removing the sizing). The power of the transmitted light was measured and the attenuation coefficient, which characterizes the fiber bundle, was determined. Although the attenuation coefficient depends on temperature and the wavelength of the light, it is independent of the power of incident light, the quality of coupling, and the length of the specimen. The refractive index of commercially available transparent resins was measured and it was proved that a resin with a refractive index lower than that of the fiber can be used to make a composite whose fibers are capable of transmitting light. The effects of temperature, compression of the fibers, and the shape of fiber ends on the power of transmitted light were examined. The measurement of emitted light can provide information about the health of the fibers. This can be the basis of a simple health monitoring system in the case of general-purpose composite structures. Full article

(This article belongs to the Section Advanced Composites)

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Open AccessArticle

In Situ Imaging during Compression of Plastic Bonded Explosives for Damage Modeling

by Virginia W. Manner, John D. Yeager, Brian M. Patterson, David J. Walters, Jamie A. Stull, Nikolaus L. Cordes, Darby J. Luscher, Kevin C. Henderson, Andrew M. Schmalzer and Bryce C. Tappan

Materials 2017, 10(6), 638; https://doi.org/10.3390/ma10060638 - 10 Jun 2017

Cited by 41 | Viewed by 6108

Abstract

The microstructure of plastic bonded explosives (PBXs) is known to influence behavior during mechanical deformation, but characterizing the microstructure can be challenging. For example, the explosive crystals and binder in formulations such as PBX 9501 do not have sufficient X-ray contrast to obtain [...] Read more.

The microstructure of plastic bonded explosives (PBXs) is known to influence behavior during mechanical deformation, but characterizing the microstructure can be challenging. For example, the explosive crystals and binder in formulations such as PBX 9501 do not have sufficient X-ray contrast to obtain three-dimensional data by in situ, absorption contrast imaging. To address this difficulty, we have formulated a series of PBXs using octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) crystals and low-density binder systems. The binders were hydroxyl-terminated polybutadiene (HTPB) or glycidyl azide polymer (GAP) cured with a commercial blend of acrylic monomers/oligomers. The binder density is approximately half of the HMX, allowing for excellent contrast using in situ X-ray computed tomography (CT) imaging. The samples were imaged during unaxial compression using micro-scale CT in an interrupted in situ modality. The rigidity of the binder was observed to significantly influence fracture, crystal-binder delamination, and flow. Additionally, 2D slices from the segmented 3D images were meshed for finite element simulation of the mesoscale response. At low stiffness, the binder and crystal do not delaminate and the crystals move with the material flow; at high stiffness, marked delamination is noted between the crystals and the binder, leading to very different mechanical properties. Initial model results exhibit qualitatively similar delamination. Full article

(This article belongs to the Section Advanced Materials Characterization)

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Open AccessArticle

Effect of Different Carbon Sources on Bacterial Nanocellulose Production and Structure Using the Low pH Resistant Strain Komagataeibacter Medellinensis

by Carlos Molina-Ramírez, Margarita Castro, Marlon Osorio, Mabel Torres-Taborda, Beatriz Gómez, Robin Zuluaga, Catalina Gómez, Piedad Gañán, Orlando J. Rojas and Cristina Castro

Materials 2017, 10(6), 639; https://doi.org/10.3390/ma10060639 - 11 Jun 2017

Cited by 104 | Viewed by 8018

Abstract

Bacterial cellulose (BC) is a polymer obtained by fermentation with microorganism of different genera. Recently, new producer species have been discovered, which require identification of the most important variables affecting cellulose production. In this work, the influence of different carbon sources in BC [...] Read more.

Bacterial cellulose (BC) is a polymer obtained by fermentation with microorganism of different genera. Recently, new producer species have been discovered, which require identification of the most important variables affecting cellulose production. In this work, the influence of different carbon sources in BC production by a novel low pH-resistant strain Komagataeibacter medellinensis was established. The Hestrin-Schramm culture medium was used as a reference and was compared to other media comprising glucose, fructose, and sucrose, used as carbon sources at three concentrations (1, 2, and 3% w/v). The BC yield and dynamics of carbon consumption were determined at given fermentation times during cellulose production. While the carbon source did not influence the BC structural characteristics, different production levels were determined: glucose > sucrose > fructose. These results highlight considerations to improve BC industrial production and to establish the BC property space for applications in different fields. Full article

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Open AccessArticle

Influence of Controlled Cooling in Bimodal Scaffold Fabrication Using Polymers with Different Melting Temperatures

by Hernan Lara-Padilla, Christian Mendoza-Buenrostro, Diego Cardenas, Aida Rodriguez-Garcia and Ciro A. Rodriguez

Materials 2017, 10(6), 640; https://doi.org/10.3390/ma10060640 - 11 Jun 2017

Cited by 20 | Viewed by 5557

Abstract

The combination of different materials and capabilities to manufacture at several scales open new possibilities in scaffold design for bone regeneration. This work is focused on bimodal scaffolds that combine polylactic acid (PLA) melt extruded strands with polycaprolactone (PCL) electrospun fibers. This type [...] Read more.

The combination of different materials and capabilities to manufacture at several scales open new possibilities in scaffold design for bone regeneration. This work is focused on bimodal scaffolds that combine polylactic acid (PLA) melt extruded strands with polycaprolactone (PCL) electrospun fibers. This type of bimodal scaffold offers better mechanical properties, compared to the use of PCL for the extruded strands, and provides potential a means for controlled drug and/or growth factor delivery through the electrospun fibers. The technologies of fused deposition modeling (FDM) and electrospinning were combined to create 3D bimodal constructs. The system uses a controlled cooling system allowing the combination of polymers with different melting temperatures to generate integrated scaffold architecture. The thermoplastic polymers used in the FDM process enhance the mechanical properties of the bimodal scaffold and control the pore structure. Integrated layers of electrospun microfibers induce an increase of the surface area for cell culture purposes, as well as potential in situ controlled drug and/or growth factor delivery. The proposed bimodal scaffolds (PLA extruded strands and PCL electrospun fibers) show appropriate morphology and better mechanical properties when compared to the use of PCL extruded strands. On average, bimodal scaffolds with overall dimensions of 30 × 30 × 2.4 mm³ (strand diameter of 0.5 mm, strand stepover of 2.5 mm, pore size of 2 mm, and layer height of 0.3 mm) showed scaffold stiffness of 23.73 MPa and compression strength of 3.85 MPa. A cytotoxicity assay based human fibroblasts showed viability of the scaffold materials. Full article

(This article belongs to the Section Biomaterials)

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Open AccessCommunication

A Novel Electro-Thermal Laminated Ceramic with Carbon-Based Layer

by Yi Ji, Bin Huang and Pinggen Rao

Materials 2017, 10(6), 641; https://doi.org/10.3390/ma10060641 - 12 Jun 2017

Viewed by 3224

Abstract

A novel electro-thermal laminated ceramic composed of ceramic tile, carbon-based layer, dielectric layer, and foaming ceramic layer was designed and prepared by tape casting. The surface temperature achieved at an applied voltage of 10 V by the laminated ceramics was 40.3 °C when [...] Read more.

A novel electro-thermal laminated ceramic composed of ceramic tile, carbon-based layer, dielectric layer, and foaming ceramic layer was designed and prepared by tape casting. The surface temperature achieved at an applied voltage of 10 V by the laminated ceramics was 40.3 °C when the thickness of carbon-based suspension was 1.0 mm and the adhesive strength between ceramic tile and carbon-based layer was 1.02 ± 0.06 MPa. In addition, the thermal aging results at 100 °C up to 192 h confirmed the high thermal stability and reliability of the electro-thermal laminated ceramics. The development of this laminated ceramic with excellent electro-thermal properties and safety provides a new individual heating device which is highly expected to be widely applied in the field of indoor heat supply. Full article

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Open AccessArticle

Aging and Curing Temperature Effects on Compressive Strength of Mortar Containing Lime Stone Quarry Dust and Industrial Granite Sludge

by Muhammad Nasir Amin, Kaffayatullah Khan, Muhammad Umair Saleem, Nauman Khurram and Muhammad Umar Khan Niazi

Materials 2017, 10(6), 642; https://doi.org/10.3390/ma10060642 - 11 Jun 2017

Cited by 26 | Viewed by 6432

Abstract

In this study, the researchers investigated the potential use of locally available waste materials from the lime stone quarry and the granite industry as a partial replacement of cement. Quarry sites and granite industry in the eastern province of Saudi Arabia produces tons [...] Read more.

In this study, the researchers investigated the potential use of locally available waste materials from the lime stone quarry and the granite industry as a partial replacement of cement. Quarry sites and granite industry in the eastern province of Saudi Arabia produces tons of powder wastes in the form of quarry dust (QD) and granite sludge (GS), respectively, causing serious environmental problems along with frequent dust storms in the area. According to ASTM C109, identical 50-mm3 specimens were cast throughout this study to evaluate the compressive strength development of mortars (7, 28 and 91 days) containing these waste materials. Experimental variables included different percentage replacement of cement with waste materials (GS, QD), fineness of GS, various curing temperatures (20, 40 and 60 °C as local normal and hot environmental temperatures) and curing moisture (continuously moist and partially moist followed by air curing). Finally, the results of mortar containing waste materials were compared to corresponding results of control mortar (CM) and mortar containing fly ash (FA). The test results indicated that under normal curing (20 °C, moist cured), the compressive strength of mortar containing the different percentage of waste materials (QD, GS, FA and their combinations) remained lower than that of CM at all ages. However, the compressive strength of mortar containing waste materials slightly increased with increased fineness of GS and significantly increased under high curing temperatures. It was recommended that more fineness of GS be achieved to use its high percentage replacement with cement (30% or more) incorporating local environmental conditions. Full article

(This article belongs to the Section Advanced Composites)

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Open AccessArticle

Anti-Caries Effects of Dental Adhesives Containing Quaternary Ammonium Methacrylates with Different Chain Lengths

by Qi Han, Bolei Li, Xuedong Zhou, Yang Ge, Suping Wang, Mingyun Li, Biao Ren, Haohao Wang, Keke Zhang, Hockin H. K. Xu, Xian Peng, Mingye Feng, Michael D. Weir, Yu Chen and Lei Cheng

Materials 2017, 10(6), 643; https://doi.org/10.3390/ma10060643 - 12 Jun 2017

Cited by 42 | Viewed by 5559

Abstract

The objectives of this study were to investigate the effects of dental adhesives containing quaternary ammonium methacrylates (QAMs) with different alkyl chain lengths (CL) on ecological caries prevention in vitro. Five QAMs were synthesized with a CL = 3, 6, 9, 12, and [...] Read more.

The objectives of this study were to investigate the effects of dental adhesives containing quaternary ammonium methacrylates (QAMs) with different alkyl chain lengths (CL) on ecological caries prevention in vitro. Five QAMs were synthesized with a CL = 3, 6, 9, 12, and 16 and incorporated into adhesives. Micro-tensile bond strength and surface charge density were used to measure the physical properties of the adhesives. The proportion change in three-species biofilms consisting of Streptococcus mutans, Streptococcus sanguinis, and Streptococcus gordonii was tested using the TaqMan real-time polymerase chain reaction. Lactic acid assay, MTT [3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay, exopolysaccharide staining, live/dead staining, scanning electron microscopy (SEM), and transverse microradiography (TMR) were performed to study the anti-biofilm and anti-demineralization effects of the dental adhesives. The results showed that incorporating QAMs with different alkyl chain lengths into the adhesives had no obvious effect on the dentin bond strength. The adhesives containing QAMs with a longer alkyl chain developed healthier biofilms. The surface charge density, anti-biofilm, and anti-demineralization effects of the adhesives increased with a CL of the QAMs from 3 to 12, but decreased slightly with a CL from 12 to 16. In conclusion, adhesives containing QAMs with a tailored chain length are promising for preventing secondary caries in an “ecological way”. Full article

(This article belongs to the Special Issue Dental Implant Materials)

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Open AccessFeature PaperArticle

Implant Stability of Biological Hydroxyapatites Used in Dentistry

by Maria Piedad Ramírez Fernández, Sergio A. Gehrke, Patricia Mazón, Jose L. Calvo-Guirado and Piedad N. De Aza

Materials 2017, 10(6), 644; https://doi.org/10.3390/ma10060644 - 12 Jun 2017

Cited by 17 | Viewed by 4597

Abstract

The aim of the present study was to monitor implant stability after sinus floor elevation with two biomaterials during the first six months of healing by resonance frequency analysis (RFA), and how physico-chemical properties affect the implant stability quotient (ISQ) at the placement [...] Read more.

The aim of the present study was to monitor implant stability after sinus floor elevation with two biomaterials during the first six months of healing by resonance frequency analysis (RFA), and how physico-chemical properties affect the implant stability quotient (ISQ) at the placement and healing sites. Bilateral maxillary sinus augmentation was performed in 10 patients in a split-mouth design using a bobine HA (BBM) as a control and porcine HA (PBM). Six months after sinus lifting, 60 implants were placed in the posterior maxilla. The ISQ was recorded on the day of surgery from RFA at T1 (baseline), T2 (three months), and T3 (six months). Statistically significant differences were found in the ISQ values during the evaluation period. The ISQ (baseline) was 63.8 ± 2.97 for BBM and 62.6 ± 2.11 for PBM. The ISQ (T2) was ~73.5 ± 4.21 and 67 ± 4.99, respectively. The ISQ (T3) was ~74.65 ± 2.93 and 72.9 ± 2.63, respectively. All of the used HAs provide osseointegration and statistical increases in the ISQ at baseline, T2 and T3 (follow-up), respectively. The BBM, sintered at high temperature with high crystallinity and low porosity, presented higher stability, which demonstrates that variations in the physico-chemical properties of a bone substitute material clearly influence implant stability. Full article

(This article belongs to the Special Issue Dental Implant Materials)

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Open AccessArticle

Anderson Insulators in Self-Assembled Gold Nanoparticles Thin Films: Single Electron Hopping between Charge Puddles Originated from Disorder

by Cheng-Wei Jiang, I-Chih Ni, Yun-Lien Hsieh, Shien-Der Tzeng, Cen-Shawn Wu and Watson Kuo

Materials 2017, 10(6), 645; https://doi.org/10.3390/ma10060645 - 12 Jun 2017

Cited by 1 | Viewed by 4730

Abstract

The Anderson insulating states in Au nanoparticle assembly are identified and studied under the application of magnetic fields and gate voltages. When the inter-nanoparticle tunneling resistance is smaller than the quantum resistance, the system showing zero Mott gap can be insulating at very [...] Read more.

The Anderson insulating states in Au nanoparticle assembly are identified and studied under the application of magnetic fields and gate voltages. When the inter-nanoparticle tunneling resistance is smaller than the quantum resistance, the system showing zero Mott gap can be insulating at very low temperature. In contrast to Mott insulators, Anderson insulators exhibit great negative magnetoresistance, inferring charge delocalization in a strong magnetic field. When probed by the electrodes spaced by ~200 nm, they also exhibit interesting gate-modulated current similar to the multi-dot single electron transistors. These results reveal the formation of charge puddles due to the interplay of disorder and quantum interference at low temperatures. Full article

(This article belongs to the Special Issue Metal-Insulator Transition)

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Open AccessArticle

Magnetically Assisted Bilayer Composites for Soft Bending Actuators

by Sung-Hwan Jang, Seon-Hong Na and Yong-Lae Park

Materials 2017, 10(6), 646; https://doi.org/10.3390/ma10060646 - 12 Jun 2017

Cited by 10 | Viewed by 6161

Abstract

This article presents a soft pneumatic bending actuator using a magnetically assisted bilayer composite composed of silicone polymer and ferromagnetic particles. Bilayer composites were fabricated by mixing ferromagnetic particles to a prepolymer state of silicone in a mold and asymmetrically distributed them by [...] Read more.

This article presents a soft pneumatic bending actuator using a magnetically assisted bilayer composite composed of silicone polymer and ferromagnetic particles. Bilayer composites were fabricated by mixing ferromagnetic particles to a prepolymer state of silicone in a mold and asymmetrically distributed them by applying a strong non-uniform magnetic field to one side of the mold during the curing process. The biased magnetic field induces sedimentation of the ferromagnetic particles toward one side of the structure. The nonhomogeneous distribution of the particles induces bending of the structure when inflated, as a result of asymmetric stiffness of the composite. The bilayer composites were then characterized with a scanning electron microscopy and thermogravimetric analysis. The bending performance and the axial expansion of the actuator were discussed for manipulation applications in soft robotics and bioengineering. The magnetically assisted manufacturing process for the soft bending actuator is a promising technique for various applications in soft robotics. Full article

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Open AccessArticle

Porous Materials from Thermally Activated Kaolinite: Preparation, Characterization and Application

by Jun Luo, Tao Jiang, Guanghui Li, Zhiwei Peng, Mingjun Rao and Yuanbo Zhang

Materials 2017, 10(6), 647; https://doi.org/10.3390/ma10060647 - 12 Jun 2017

Cited by 13 | Viewed by 4148

Abstract

In the present study, porous alumina/silica materials were prepared by selective leaching of silicon/aluminum constituents from thermal-activated kaolinite in inorganic acid or alkali liquor. The correlations between the characteristics of the prepared porous materials and the dissolution properties of activated kaolinite were also [...] Read more.

In the present study, porous alumina/silica materials were prepared by selective leaching of silicon/aluminum constituents from thermal-activated kaolinite in inorganic acid or alkali liquor. The correlations between the characteristics of the prepared porous materials and the dissolution properties of activated kaolinite were also investigated. The results show that the specific surface area (SSA) of porous alumina/silica increases with silica/alumina dissolution, but without marked change of the BJH pore size. Furthermore, change in pore volume is more dependent on activation temperature. The porous alumina and silica obtained from alkali leaching of kaolinite activated at 1150 °C for 15 min and acid leaching of kaolinite activated at 850 °C for 15 min are mesoporous, with SSAs, BJH pore sizes and pore volumes of 55.8 m²/g and 280.3 m²/g, 6.06 nm and 3.06 nm, 0.1455 mL/g and 0.1945 mL/g, respectively. According to the adsorption tests, porous alumina has superior adsorption capacities for Cu²⁺, Pb²⁺ and Cd²⁺ compared with porous silica and activated carbon. The maximum capacities of porous alumina for Cu²⁺, Pb²⁺ and Cd²⁺ are 134 mg/g, 183 mg/g and 195 mg/g, respectively, at 30 °C. Full article

(This article belongs to the Section Porous Materials)

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Open AccessArticle

Lamb Wave Damage Quantification Using GA-Based LS-SVM

by Fuqiang Sun, Ning Wang, Jingjing He, Xuefei Guan and Jinsong Yang

Materials 2017, 10(6), 648; https://doi.org/10.3390/ma10060648 - 12 Jun 2017

Cited by 40 | Viewed by 5126

Abstract

Lamb waves have been reported to be an efficient tool for non-destructive evaluations (NDE) for various application scenarios. However, accurate and reliable damage quantification using the Lamb wave method is still a practical challenge, due to the complex underlying mechanism of Lamb wave [...] Read more.

Lamb waves have been reported to be an efficient tool for non-destructive evaluations (NDE) for various application scenarios. However, accurate and reliable damage quantification using the Lamb wave method is still a practical challenge, due to the complex underlying mechanism of Lamb wave propagation and damage detection. This paper presents a Lamb wave damage quantification method using a least square support vector machine (LS-SVM) and a genetic algorithm (GA). Three damage sensitive features, namely, normalized amplitude, phase change, and correlation coefficient, were proposed to describe changes of Lamb wave characteristics caused by damage. In view of commonly used data-driven methods, the GA-based LS-SVM model using the proposed three damage sensitive features was implemented to evaluate the crack size. The GA method was adopted to optimize the model parameters. The results of GA-based LS-SVM were validated using coupon test data and lap joint component test data with naturally developed fatigue cracks. Cases of different loading and manufacturer were also included to further verify the robustness of the proposed method for crack quantification. Full article

(This article belongs to the Special Issue Structural Health Monitoring for Aerospace Applications 2017)

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Open AccessArticle

Methodology for the Assessment of the Ecotoxicological Potential of Construction Materials

by Patrícia Rodrigues, José D. Silvestre, Inês Flores-Colen, Cristina A. Viegas, Jorge De Brito, Rawaz Kurad and Martha Demertzi

Materials 2017, 10(6), 649; https://doi.org/10.3390/ma10060649 - 13 Jun 2017

Cited by 43 | Viewed by 4537

Abstract

Innovation in construction materials (CM) implies changing their composition by incorporating raw materials, usually non-traditional ones, which confer the desired characteristics. However, this practice may have unknown risks. This paper discusses the ecotoxicological potential associated with raw and construction materials, and proposes and [...] Read more.

Innovation in construction materials (CM) implies changing their composition by incorporating raw materials, usually non-traditional ones, which confer the desired characteristics. However, this practice may have unknown risks. This paper discusses the ecotoxicological potential associated with raw and construction materials, and proposes and applies a methodology for the assessment of their ecotoxicological potential. This methodology is based on existing laws, such as Regulation (European Commission) No. 1907/2006 (REACH—Registration, Evaluation, Authorization and Restriction of Chemicals) and Regulation (European Commission) No. 1272/2008 (CLP—Classification, Labelling and Packaging). Its application and validation showed that raw material without clear evidence of ecotoxicological potential, but with some ability to release chemicals, can lead to the formulation of a CM with a slightly lower hazardousness in terms of chemical characterization despite a slightly higher ecotoxicological potential than the raw materials. The proposed methodology can be a useful tool for the development and manufacturing of products and the design choice of the most appropriate CM, aiming at the reduction of their environmental impact and contributing to construction sustainability. Full article

(This article belongs to the Section Advanced Materials Characterization)

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Open AccessArticle

Synthesis of Au NP@MoS₂ Quantum Dots Core@Shell Nanocomposites for SERS Bio-Analysis and Label-Free Bio-Imaging

by Xixi Fei, Zhiming Liu, Yuqing Hou, Yi Li, Guangcun Yang, Chengkang Su, Zhen Wang, Huiqing Zhong, Zhengfei Zhuang and Zhouyi Guo

Materials 2017, 10(6), 650; https://doi.org/10.3390/ma10060650 - 13 Jun 2017

Cited by 28 | Viewed by 8075

Abstract

In this work, we report a facile method using MoS₂ quantum dots (QDs) as reducers to directly react with HAuCl₄ for the synthesis of Au nanoparticle@MoS₂ quantum dots (Au NP@MoS₂ QDs) core@shell nanocomposites with an ultrathin shell of ca. [...] Read more.

In this work, we report a facile method using MoS₂ quantum dots (QDs) as reducers to directly react with HAuCl₄ for the synthesis of Au nanoparticle@MoS₂ quantum dots (Au NP@MoS₂ QDs) core@shell nanocomposites with an ultrathin shell of ca. 1 nm. The prepared Au NP@MoS₂ QDs reveal high surface enhanced Raman scattering (SERS) performance regarding sensitivity as well as the satisfactory SERS reproducibility and stability. The limit of detection of the hybrids for crystal violet can reach 0.5 nM with a reasonable linear response range from 0.5 μM to 0.5 nM (R² ≈ 0.974). Furthermore, the near-infrared SERS detection based on Au NP@MoS₂ QDs in living cells is achieved with distinct Raman signals which are clearly assigned to the various cellular components. Meanwhile, the distinguishable SERS images are acquired from the 4T1 cells with the incubation of Au NP@MoS₂ QDs. Consequently, the straightforward strategy of using Au NP@MoS₂ QDs exhibits great potential as a superior SERS substrate for chemical and biological detection as well as bio-imaging. Full article

(This article belongs to the Special Issue Ultrathin Two-dimensional (2D) Nanomaterials)

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Open AccessArticle

Understanding Drug Release Data through Thermodynamic Analysis

by Marjorie Caroline Liberato Cavalcanti Freire, Francisco Alexandrino, Henrique Rodrigues Marcelino, Paulo Henrique de Souza Picciani, Kattya Gyselle de Holanda e Silva, Julieta Genre, Anselmo Gomes de Oliveira and Eryvaldo Sócrates Tabosa do Egito

Materials 2017, 10(6), 651; https://doi.org/10.3390/ma10060651 - 13 Jun 2017

Cited by 51 | Viewed by 4787

Abstract

Understanding the factors that can modify the drug release profile of a drug from a Drug-Delivery-System (DDS) is a mandatory step to determine the effectiveness of new therapies. The aim of this study was to assess the Amphotericin-B (AmB) kinetic release profiles from [...] Read more.

Understanding the factors that can modify the drug release profile of a drug from a Drug-Delivery-System (DDS) is a mandatory step to determine the effectiveness of new therapies. The aim of this study was to assess the Amphotericin-B (AmB) kinetic release profiles from polymeric systems with different compositions and geometries and to correlate these profiles with the thermodynamic parameters through mathematical modeling. Film casting and electrospinning techniques were used to compare behavior of films and fibers, respectively. Release profiles from the DDSs were performed, and the mathematical modeling of the data was carried out. Activation energy, enthalpy, entropy and Gibbs free energy of the drug release process were determined. AmB release profiles showed that the relationship to overcome the enthalpic barrier was PVA-fiber > PVA-film > PLA-fiber > PLA-film. Drug release kinetics from the fibers and the films were better fitted on the Peppas–Sahlin and Higuchi models, respectively. The thermodynamic parameters corroborate these findings, revealing that the AmB release from the evaluated systems was an endothermic and non-spontaneous process. Thermodynamic parameters can be used to explain the drug kinetic release profiles. Such an approach is of utmost importance for DDS containing insoluble compounds, such as AmB, which is associated with an erratic bioavailability. Full article

(This article belongs to the Section Biomaterials)

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Open AccessArticle

Lamb Wave-Based Structural Health Monitoring on Composite Bolted Joints under Tensile Load

by Bin Yang, Fu-Zhen Xuan, Yanxun Xiang, Dan Li, Wujun Zhu, Xiaojun Tang, Jichao Xu, Kang Yang and Chengqiang Luo

Materials 2017, 10(6), 652; https://doi.org/10.3390/ma10060652 - 14 Jun 2017

Cited by 45 | Viewed by 7173

Abstract

Online and offline monitoring of composite bolted joints under tensile load were investigated using piezoelectric transducers. The relationships between Lamb wave signals, pre-tightening force, the applied tensile load, as well as the failure modes were investigated. Results indicated that S0/A0 wave [...] Read more.

Online and offline monitoring of composite bolted joints under tensile load were investigated using piezoelectric transducers. The relationships between Lamb wave signals, pre-tightening force, the applied tensile load, as well as the failure modes were investigated. Results indicated that S0/A0 wave amplitudes decrease with the increasing of load. Relationships between damage features and S0/A0 mode were built based on the finite element (FE) simulation and experimental results. The possibility of application of Lamb wave-based structure health monitoring in bolted joint-like composite structures was thus achieved. Full article

(This article belongs to the Special Issue Structural Health Monitoring for Aerospace Applications 2017)

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Open AccessArticle

Simultaneously Toughening and Strengthening Soy Protein Isolate-Based Composites via Carboxymethylated Chitosan and Halloysite Nanotube Hybridization

by Xiaorong Liu, Haijiao Kang, Zhong Wang, Wei Zhang, Jianzhang Li and Shifeng Zhang

Materials 2017, 10(6), 653; https://doi.org/10.3390/ma10060653 - 14 Jun 2017

Cited by 43 | Viewed by 5539

Abstract

Chemical cross-linking modification can significantly enhance the tensile strength (TS) of soy protein isolate (SPI)-based composites, but usually at the cost of a reduction in the elongation at break (EB). In this study, eco-friendly and high-potential hybrid SPI-based nanocomposites with improved TS were [...] Read more.

Chemical cross-linking modification can significantly enhance the tensile strength (TS) of soy protein isolate (SPI)-based composites, but usually at the cost of a reduction in the elongation at break (EB). In this study, eco-friendly and high-potential hybrid SPI-based nanocomposites with improved TS were fabricated without compromising the reduction of EB. The hybrid of carboxymethylated chitosan (CMCS) and halloysite nanotubes (HNTs) as the enhancement center was added to the SPI and 1,2,3-propanetriol-diglycidyl-ether (PTGE) solution. The chemical structure, crystallinity, micromorphology, and opacity properties of the obtained SPI/PTGE/HNTs/CMCS film was analyzed by the attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV-Vis spectroscopy. The results indicated that HNTs were uniformly dispersed in the SPI matrix without crystal structure damages. Compared to the SPI/PTGE film, the TS and EB of the SPI/PTGE/HNTs/CMCS film were increased by 57.14% and 27.34%, reaching 8.47 MPa and 132.12%, respectively. The synergy of HNTs and CMCS via electrostatic interactions also improved the water resistance of the SPI/PTGE/HNTs/CMCS film. These films may have considerable potential in the field of sustainable and environmentally friendly packaging. Full article

(This article belongs to the Section Biomaterials)

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Open AccessArticle

Effect of Zinc Phosphate on the Corrosion Behavior of Waterborne Acrylic Coating/Metal Interface

by Hongxia Wan, Dongdong Song, Xiaogang Li, Dawei Zhang, Jin Gao and Cuiwei Du

Materials 2017, 10(6), 654; https://doi.org/10.3390/ma10060654 - 14 Jun 2017

Cited by 34 | Viewed by 6979

Abstract

Waterborne coating has recently been paid much attention. However, it cannot be used widely due to its performance limitations. Under the specified conditions of the selected resin, selecting the function pigment is key to improving the anticorrosive properties of the coating. Zinc phosphate [...] Read more.

Waterborne coating has recently been paid much attention. However, it cannot be used widely due to its performance limitations. Under the specified conditions of the selected resin, selecting the function pigment is key to improving the anticorrosive properties of the coating. Zinc phosphate is an environmentally protective and efficient anticorrosion pigment. In this work, zinc phosphate was used in modifying waterborne acrylic coatings. Moreover, the disbonding resistance of the coating was studied. Results showed that adding zinc phosphate can effectively inhibit the anode process of metal corrosion and enhance the wet adhesion of the coating, and consequently prevent the horizontal diffusion of the corrosive medium into the coating/metal interface and slow down the disbonding of the coating. Full article

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Open AccessArticle

Microstructure and Dielectric Properties of LPCVD/CVI-SiBCN Ceramics Annealed at Different Temperatures

by Jianping Li, Mingxi Zhao, Yongsheng Liu, Nan Chai, Fang Ye, Hailong Qin, Laifei Cheng and Litong Zhang

Materials 2017, 10(6), 655; https://doi.org/10.3390/ma10060655 - 15 Jun 2017

Cited by 11 | Viewed by 4603

Abstract

SiBCN ceramics were introduced into porous Si₃N₄ ceramics via a low-pressure chemical vapor deposition and infiltration (LPCVD/CVI) technique, and then the composite ceramics were heat-treated from 1400 °C to 1700 °C in a N₂ atmosphere. The effects of annealing [...] Read more.

SiBCN ceramics were introduced into porous Si₃N₄ ceramics via a low-pressure chemical vapor deposition and infiltration (LPCVD/CVI) technique, and then the composite ceramics were heat-treated from 1400 °C to 1700 °C in a N₂ atmosphere. The effects of annealing temperatures on microstructure, phase evolution, dielectric properties of SiBCN ceramics were investigated. The results revealed that α-Si₃N₄ and free carbon were separated below 1700 °C, and then SiC grains formed in the SiBCN ceramic matrix after annealing at 1700 °C through a phase-reaction between free carbon and α-Si₃N₄. The average dielectric loss of composites increased from 0 to 0.03 due to the formation of dispersive SiC grains and the increase of grain boundaries. Full article

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Open AccessArticle

Crack Identification in CFRP Laminated Beams Using Multi-Resolution Modal Teager–Kaiser Energy under Noisy Environments

by Wei Xu, Maosen Cao, Keqin Ding, Maciej Radzieński and Wiesław Ostachowicz

Materials 2017, 10(6), 656; https://doi.org/10.3390/ma10060656 - 15 Jun 2017

Cited by 14 | Viewed by 4376

Abstract

Carbon fiber reinforced polymer laminates are increasingly used in the aerospace and civil engineering fields. Identifying cracks in carbon fiber reinforced polymer laminated beam components is of considerable significance for ensuring the integrity and safety of the whole structures. With the development of [...] Read more.

Carbon fiber reinforced polymer laminates are increasingly used in the aerospace and civil engineering fields. Identifying cracks in carbon fiber reinforced polymer laminated beam components is of considerable significance for ensuring the integrity and safety of the whole structures. With the development of high-resolution measurement technologies, mode-shape-based crack identification in such laminated beam components has become an active research focus. Despite its sensitivity to cracks, however, this method is susceptible to noise. To address this deficiency, this study proposes a new concept of multi-resolution modal Teager–Kaiser energy, which is the Teager–Kaiser energy of a mode shape represented in multi-resolution, for identifying cracks in carbon fiber reinforced polymer laminated beams. The efficacy of this concept is analytically demonstrated by identifying cracks in Timoshenko beams with general boundary conditions; and its applicability is validated by diagnosing cracks in a carbon fiber reinforced polymer laminated beam, whose mode shapes are precisely acquired via non-contact measurement using a scanning laser vibrometer. The analytical and experimental results show that multi-resolution modal Teager–Kaiser energy is capable of designating the presence and location of cracks in these beams under noisy environments. This proposed method holds promise for developing crack identification systems for carbon fiber reinforced polymer laminates. Full article

(This article belongs to the Special Issue Structural Health Monitoring for Aerospace Applications 2017)

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Open AccessArticle

Warm White Light-Emitting Diodes Based on a Novel Orange Cationic Iridium(III) Complex

by Huaijun Tang, Guoyun Meng, Zeyu Chen, Kaimin Wang, Qiang Zhou and Zhengliang Wang

Materials 2017, 10(6), 657; https://doi.org/10.3390/ma10060657 - 16 Jun 2017

Cited by 12 | Viewed by 5084

Abstract

A novel orange cationic iridium(III) complex [(TPTA)₂Ir(dPPOA)]PF₆ (TPTA: 3,4,5-triphenyl-4H-1,2,4-triazole, dPPOA: N,N-diphenyl-4-(5-(pyridin-2-yl)-1,3,4-oxadiazol-2-yl)aniline) was synthesized and used as a phosphor in light-emitting diodes (LEDs). [(TPTA)₂Ir(dPPOA)]PF₆ has high thermal stability with a decomposition temperature (T_d) [...] Read more.

A novel orange cationic iridium(III) complex [(TPTA)₂Ir(dPPOA)]PF₆ (TPTA: 3,4,5-triphenyl-4H-1,2,4-triazole, dPPOA: N,N-diphenyl-4-(5-(pyridin-2-yl)-1,3,4-oxadiazol-2-yl)aniline) was synthesized and used as a phosphor in light-emitting diodes (LEDs). [(TPTA)₂Ir(dPPOA)]PF₆ has high thermal stability with a decomposition temperature (T_d) of 375 °C, and its relative emission intensity at 100 °C is 88.8% of that at 25°C. When only [(TPTA)₂Ir(dPPOA)]PF₆ was used as a phosphor at 6.0 wt % in silicone and excited by a blue GaN (GaN: gallium nitride) chip (450 nm), an orange LED was obtained. A white LED fabricated by a blue GaN chip (450 nm) and only yellow phosphor Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce) (1.0 wt % in silicone) emitted cold white light, its CIE (CIE: Commission International de I’Eclairage) value was (0.32, 0.33), color rendering index (CRI) was 72.2, correlated color temperature (CCT) was 6877 K, and luminous efficiency (η_L) was 128.5 lm∙W⁻¹. Such a cold white LED became a neutral white LED when [(TPTA)₂Ir(dPPOA)]PF₆ was added at 0.5 wt %; its corresponding CIE value was (0.35, 0.33), CRI was 78.4, CCT was 4896 K, and η_L was 85.2 lm∙W⁻¹. It further became a warm white LED when [(TPTA)₂Ir(dPPOA)]PF₆ was added at 1.0 wt %; its corresponding CIE value was (0.39, 0.36), CRI was 80.2, CCT was 3473 K, and η_L was 46.1 lm∙W⁻¹. The results show that [(TPTA)₂Ir(dPPOA)]PF₆ is a promising phosphor candidate for fabricating warm white LEDs. Full article

(This article belongs to the Special Issue Luminescent Materials 2017)

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Open AccessArticle

Fatigue Lifetime of Ceramic Matrix Composites at Intermediate Temperature by Acoustic Emission

by Elie Racle, Nathalie Godin, Pascal Reynaud and Gilbert Fantozzi

Materials 2017, 10(6), 658; https://doi.org/10.3390/ma10060658 - 16 Jun 2017

Cited by 31 | Viewed by 5261

Abstract

The fatigue behavior of a Ceramic Matrix Composite (CMC) at intermediate temperature under air is investigated. Because of the low density and the high tensile strength of CMC, they offer a good technical solution to design aeronautical structural components. The aim of the [...] Read more.

The fatigue behavior of a Ceramic Matrix Composite (CMC) at intermediate temperature under air is investigated. Because of the low density and the high tensile strength of CMC, they offer a good technical solution to design aeronautical structural components. The aim of the present study is to compare the behavior of this composite under static and cyclic loading. Comparison between incremental static and cyclic tests shows that cyclic loading with an amplitude higher than 30% of the ultimate tensile strength has significant effects on damage and material lifetimes. In order to evaluate the remaining lifetime, several damage indicators, mainly based on the investigation of the liberated energy, are introduced. These indicators highlight critical times or characteristic times, allowing an evaluation of the remaining lifetime. A link is established with the characteristic time around 25% of the total test duration and the beginning of the matrix cracking during cyclic fatigue. Full article

(This article belongs to the Special Issue The Life of Materials at High Temperatures)

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Open AccessArticle

Characterization of Antimicrobial Poly (Lactic Acid)/Nano-Composite Films with Silver and Zinc Oxide Nanoparticles

by Zhuangzhuang Chu, Tianrui Zhao, Lin Li, Jian Fan and Yuyue Qin

Materials 2017, 10(6), 659; https://doi.org/10.3390/ma10060659 - 16 Jun 2017

Cited by 147 | Viewed by 7244

Abstract

Antimicrobial active films based on poly (lactic acid) (PLA) were prepared with nano-silver (nano-Ag) and nano-zinc oxide (nano-ZnO) using a solvent volatilizing method. The films were characterized for mechanical, structural, thermal, physical and antimicrobial properties. Scanning electron microscopy (SEM) images characterized the fracture [...] Read more.

Antimicrobial active films based on poly (lactic acid) (PLA) were prepared with nano-silver (nano-Ag) and nano-zinc oxide (nano-ZnO) using a solvent volatilizing method. The films were characterized for mechanical, structural, thermal, physical and antimicrobial properties. Scanning electron microscopy (SEM) images characterized the fracture morphology of the films with different contents of nano-Ag and nano-ZnO. The addition of nanoparticles into the pure PLA film decreased the tensile strength and elasticity modulus and increased the elongation of breaks—in other words, the flexibility and extensibility of these composites improved. According to the results of differential scanning calorimetry (DSC), the glass transition temperature of the PLA nano-composite films decreased, and the crystallinity of these films increased; a similar result was apparent from X-ray diffraction (XRD) analysis. The water vapor permeability (WVP) and opacity of the PLA nano-composite films augmented compared with pure PLA film. Incorporation of nanoparticles to the PLA films significantly improved the antimicrobial activity to inhibit the growth of Escherichia coli. The results indicated that PLA films with nanoparticles could be considered a potential environmental-friendly packaging material. Full article

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Open AccessArticle

Experimental Investigation of the Acoustic Nonlinear Behavior in Granular Polymer Bonded Explosives with Progressive Fatigue Damage

by Zhanfeng Yang, Yong Tian, Weibin Li, Haiqiang Zhou, Weibin Zhang and Jingming Li

Materials 2017, 10(6), 660; https://doi.org/10.3390/ma10060660 - 16 Jun 2017

Cited by 15 | Viewed by 4049

Abstract

The measurement of acoustic nonlinear response is known as a promising technique to characterize material micro-damages. In this paper, nonlinear ultrasonic approach is used to characterize the evolution of fatigue induced micro-cracks in polymer bonded explosives. The variations of acoustic nonlinearity with respect [...] Read more.

The measurement of acoustic nonlinear response is known as a promising technique to characterize material micro-damages. In this paper, nonlinear ultrasonic approach is used to characterize the evolution of fatigue induced micro-cracks in polymer bonded explosives. The variations of acoustic nonlinearity with respect to fatigue cycles in the specimens are obtained in this investigation. The present results show a significant increase of acoustic nonlinearity with respect to fatigue cycles. The experimental observation of the correlation between the acoustic nonlinearity and fatigue cycles in carbon/epoxy laminates, verifies that an acoustic nonlinear response can be used to evaluate the progressive fatigue damage in the granular polymer bonded explosives. The sensitivity comparison of nonlinear and linear parameters of ultrasonic waves in the specimens shows that nonlinear acoustic parameters are more promising indicators to fatigue induced micro-damage than linear ones. The feasibility study of the micro-damage assessment of polymer bonded explosives by nonlinear ultrasonic technique in this work can be applied to damage identification, material degradation monitoring, and lifetime prediction of the explosive parts. Full article

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Open AccessFeature PaperCommunication

Probing Transition-Metal Silicides as PGM-Free Catalysts for Hydrogen Oxidation and Evolution in Acidic Medium

by Thomas Mittermeier, Pankaj Madkikar, Xiaodong Wang, Hubert A. Gasteiger and Michele Piana

Materials 2017, 10(6), 661; https://doi.org/10.3390/ma10060661 - 16 Jun 2017

Cited by 16 | Viewed by 6160

Abstract

In this experimental study, we investigate various transition-metal silicides as platinum-group-metal-(PGM)-free electrocatalysts for the hydrogen oxidation reaction (HOR), and for the hydrogen evolution reaction (HER) in acidic environment for the first time. Using cyclic voltammetry in 0.1 M HClO₄, we first [...] Read more.

In this experimental study, we investigate various transition-metal silicides as platinum-group-metal-(PGM)-free electrocatalysts for the hydrogen oxidation reaction (HOR), and for the hydrogen evolution reaction (HER) in acidic environment for the first time. Using cyclic voltammetry in 0.1 M HClO₄, we first demonstrate that the tested materials exhibit sufficient stability against dissolution in the relevant potential window. Further, we determine the HOR and HER activities for Mo, W, Ta, Ni and Mo-Ni silicides in rotating disk electrode experiments. In conclusion, for the HOR only Ni₂Si shows limited activity, and the HER activity of the investigated silicides is considerably lower compared to other PGM-free HER catalysts reported in the literature. Full article

(This article belongs to the Special Issue Advanced Materials in Polymer Electrolyte Fuel Cells)

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Open AccessArticle

Nanoscaled Mechanical Properties of Cement Composites Reinforced with Carbon Nanofibers

by Salim Barbhuiya and PengLoy Chow

Materials 2017, 10(6), 662; https://doi.org/10.3390/ma10060662 - 16 Jun 2017

Cited by 30 | Viewed by 4285

Abstract

This paper reports the effects of carbon nanofibers (CNFs) on nanoscaled mechanical properties of cement composites. CNFs were added to cement composites at the filler loading of 0.2 wt % (by wt. of cement). Micrographs based on scanning electron microscopy (SEM) show that [...] Read more.

This paper reports the effects of carbon nanofibers (CNFs) on nanoscaled mechanical properties of cement composites. CNFs were added to cement composites at the filler loading of 0.2 wt % (by wt. of cement). Micrographs based on scanning electron microscopy (SEM) show that CNFs are capable of forming strong interfacial bonding with cement matrices. Experimental results using nanoindentation reveal that the addition of CNFs in cement composites increases the proportions of high-density calcium-silicate-hydrate gel (HD-CSH) compared to low-density CSH gel. It was also found that the inclusion of CNFs increases the compressive strength of cement composites. Full article

(This article belongs to the Special Issue Improving Performance of Nanocomposite Materials)

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Open AccessFeature PaperArticle

Ultra High Strain Rate Nanoindentation Testing

by Pardhasaradhi Sudharshan Phani and Warren Carl Oliver

Materials 2017, 10(6), 663; https://doi.org/10.3390/ma10060663 - 17 Jun 2017

Cited by 51 | Viewed by 6719

Abstract

Strain rate dependence of indentation hardness has been widely used to study time-dependent plasticity. However, the currently available techniques limit the range of strain rates that can be achieved during indentation testing. Recent advances in electronics have enabled nanomechanical measurements with very low [...] Read more.

Strain rate dependence of indentation hardness has been widely used to study time-dependent plasticity. However, the currently available techniques limit the range of strain rates that can be achieved during indentation testing. Recent advances in electronics have enabled nanomechanical measurements with very low noise levels (sub nanometer) at fast time constants (20 µs) and high data acquisition rates (100 KHz). These capabilities open the doors for a wide range of ultra-fast nanomechanical testing, for instance, indentation testing at very high strain rates. With an accurate dynamic model and an instrument with fast time constants, step load tests can be performed which enable access to indentation strain rates approaching ballistic levels (i.e., 4000 1/s). A novel indentation based testing technique involving a combination of step load and constant load and hold tests that enables measurement of strain rate dependence of hardness spanning over seven orders of magnitude in strain rate is presented. A simple analysis is used to calculate the equivalent uniaxial response from indentation data and compared to the conventional uniaxial data for commercial purity aluminum. Excellent agreement is found between the indentation and uniaxial data over several orders of magnitude of strain rate. Full article

(This article belongs to the Special Issue Advanced Nanoindentation in Materials)

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Open AccessArticle

Soft Ionic Electroactive Polymer Actuators with Tunable Non-Linear Angular Deformation

by Wangyujue Hong, Abdallah Almomani, Yuanfen Chen, Reihaneh Jamshidi and Reza Montazami

Materials 2017, 10(6), 664; https://doi.org/10.3390/ma10060664 - 21 Jun 2017

Cited by 17 | Viewed by 4459

Abstract

The most rational approach to fabricate soft robotics is the implementation of soft actuators. Conventional soft electromechanical actuators exhibit linear or circular deformation, based on their design. This study presents the use of conjugated polymers, Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) to locally vary ion permeability of [...] Read more.

The most rational approach to fabricate soft robotics is the implementation of soft actuators. Conventional soft electromechanical actuators exhibit linear or circular deformation, based on their design. This study presents the use of conjugated polymers, Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) to locally vary ion permeability of the ionic electroactive polymer actuators and manipulate ion motion through means of structural design to realize intrinsic angular deformation. Such angular deformations are closer to biomimetic systems and have potential applications in bio-robotics. Electrochemical studies reveal that the mechanism of actuation is mainly associated with the charging of electric double layer (EDL) capacitors by ion accumulation and the PEDOT:PSS layer’s expansion by ion interchange and penetration. Dependence of actuator deformation on structural design is studied experimentally and conclusions are verified by analytical and finite element method modeling. The results suggest that the ion-material interactions are considerably dominated by the design of the drop-cast PEDOT:PSS on Nafion. Full article

(This article belongs to the Section Advanced Materials Characterization)

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Open AccessArticle

Thermal Stability and Fire Properties of Salen and Metallosalens as Fire Retardants in Thermoplastic Polyurethane (TPU)

by Aditya Ramgobin, Gaëlle Fontaine, Christophe Penverne and Serge Bourbigot

Materials 2017, 10(6), 665; https://doi.org/10.3390/ma10060665 - 17 Jun 2017

Cited by 35 | Viewed by 6262

Abstract

This study deals with the synthesis and evaluation of salen based derivatives as fire retardants in thermoplastic polyurethane. Salens, hydroxysalens and their first row transition metal complexes (salen-M) were synthesized (Copper, Manganese, Nickel and Zinc). They were then incorporated in thermoplastic polyurethane (TPU) [...] Read more.

This study deals with the synthesis and evaluation of salen based derivatives as fire retardants in thermoplastic polyurethane. Salens, hydroxysalens and their first row transition metal complexes (salen-M) were synthesized (Copper, Manganese, Nickel and Zinc). They were then incorporated in thermoplastic polyurethane (TPU) with a loading as low as 10:1 weight ratio. The thermal stability as well as the fire properties of the formulations were evaluated. Thermogravimetric analysis (TGA) showed that different coordination metals on the salen could induce different decomposition pathways when mixed with TPU. The Pyrolysis Combustion Flow Calorimetry (PCFC) results showed that some M-salen have the ability to significantly decrease the peak heat release rate (−61% compared to neat TPU) and total heat released (−63% compared to neat TPU) when formulated at 10:1 wt % ratio in TPU. Mass Loss Cone Calorimetry (MLC) results have shown that some additives (salen-Cu and salen-Mn) exhibit very promising performance and they are good candidates as flame-retardants for TPU. Full article

(This article belongs to the Special Issue Flame Retardant Polymeric Materials)

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Open AccessArticle

Mechanical Behavior of Steel Fiber-Reinforced Concrete Beams Bonded with External Carbon Fiber Sheets

by Viktor Gribniak, Vytautas Tamulenas, Pui-Lam Ng, Aleksandr K. Arnautov, Eugenijus Gudonis and Ieva Misiunaite

Materials 2017, 10(6), 666; https://doi.org/10.3390/ma10060666 - 17 Jun 2017

Cited by 36 | Viewed by 7647

Abstract

This study investigates the mechanical behavior of steel fiber-reinforced concrete (SFRC) beams internally reinforced with steel bars and externally bonded with carbon fiber-reinforced polymer (CFRP) sheets fixed by adhesive and hybrid jointing techniques. In particular, attention is paid to the load resistance and [...] Read more.

This study investigates the mechanical behavior of steel fiber-reinforced concrete (SFRC) beams internally reinforced with steel bars and externally bonded with carbon fiber-reinforced polymer (CFRP) sheets fixed by adhesive and hybrid jointing techniques. In particular, attention is paid to the load resistance and failure modes of composite beams. The steel fibers were used to avoiding the rip-off failure of the concrete cover. The CFRP sheets were fixed to the concrete surface by epoxy adhesive as well as combined with various configurations of small-diameter steel pins for mechanical fastening to form a hybrid connection. Such hybrid jointing techniques were found to be particularly advantageous in avoiding brittle debonding failure, by promoting progressive failure within the hybrid joints. The use of CFRP sheets was also effective in suppressing the localization of the discrete cracks. The development of the crack pattern was monitored using the digital image correlation method. As revealed from the image analyses, with an appropriate layout of the steel pins, brittle failure of the concrete-carbon fiber interface could be effectively prevented. Inverse analysis of the moment-curvature diagrams was conducted, and it was found that a simplified tension-stiffening model with a constant residual stress level at 90% of the strength of the SFRC is adequate for numerically simulating the deformation behavior of beams up to the debonding of the CFRP sheets. Full article

(This article belongs to the Section Advanced Composites)

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Open AccessArticle

Biosynthesis and Characterization of AgNPs–Silk/PVA Film for Potential Packaging Application

by Gang Tao, Rui Cai, Yejing Wang, Kai Song, Pengchao Guo, Ping Zhao, Hua Zuo and Huawei He

Materials 2017, 10(6), 667; https://doi.org/10.3390/ma10060667 - 17 Jun 2017

Cited by 40 | Viewed by 7229

Abstract

Bionanocomposite packaging materials have a bright future for a broad range of applications in the food and biomedical industries. Antimicrobial packaging is one of the bionanocomposite packaging materials. Silver nanoparticle (AgNP) is one of the most attractive antimicrobial agents for its broad spectrum [...] Read more.

Bionanocomposite packaging materials have a bright future for a broad range of applications in the food and biomedical industries. Antimicrobial packaging is one of the bionanocomposite packaging materials. Silver nanoparticle (AgNP) is one of the most attractive antimicrobial agents for its broad spectrum of antimicrobial activity against microorganisms. However, the traditional method of preparing AgNPs-functionalized packaging material is cumbersome and not environmentally friendly. To develop an efficient and convenient biosynthesis method to prepare AgNPs-modified bionanocomposite material for packaging applications, we synthesized AgNPs in situ in a silk fibroin solution via the reduction of Ag⁺ by the tyrosine residue of fibroin, and then prepared AgNPs–silk/poly(vinyl alcohol) (PVA) composite film by blending with PVA. AgNPs were synthesized evenly on the surface or embedded in the interior of silk/PVA film. The prepared AgNPs–silk/PVA film exhibited excellent mechanical performance and stability, as well as good antibacterial activity against both Gram-negative and Gram-positive bacteria. AgNPs–silk/PVA film offers more choices to be potentially applied in the active packaging field. Full article

(This article belongs to the Special Issue Improving Performance of Nanocomposite Materials)

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Open AccessArticle

Synthesis and Characterization of Bio-Oil Phenol Formaldehyde Resin Used to Fabricate Phenolic Based Materials

by Yong Cui, Xiaopeng Hou, Wenliang Wang and Jianmin Chang

Materials 2017, 10(6), 668; https://doi.org/10.3390/ma10060668 - 18 Jun 2017

Cited by 54 | Viewed by 6160

Abstract

In this study, bio-oil from the fast pyrolysis of renewable biomass was used as the raw material to synthesize bio-oil phenol formaldehyde (BPF) resin—a desirable resin for fabricating phenolic-based material. During the synthesis process, paraformaldehyde was used to achieve the requirement of high [...] Read more.

In this study, bio-oil from the fast pyrolysis of renewable biomass was used as the raw material to synthesize bio-oil phenol formaldehyde (BPF) resin—a desirable resin for fabricating phenolic-based material. During the synthesis process, paraformaldehyde was used to achieve the requirement of high solid content and low viscosity. The properties of BPF resins were tested. Results indicated that BPF resin with the bio-oil addition of 20% had good performance on oxygen index and bending strength, indicating that adding bio-oil could modify the fire resistance and brittleness of PF resin. The thermal curing behavior and heat resistance of BPF resins were investigated by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). Results showed that adding bio-oil had an impact on curing characteristics and thermal degradation process of PF resin, but the influence was insignificant when the addition was relatively low. The chemical structure and surface characteristics of BPF resins were determined by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The analysis demonstrated that adding bio-oil in the amount of 20% was able to improve the crosslinking degree and form more hydrocarbon chains in PF resin. Full article

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Open AccessArticle

Influence of Tension Stiffening on the Flexural Stiffness of Reinforced Concrete Circular Sections

by Francesco Morelli, Cosimo Amico, Walter Salvatore, Nunziante Squeglia and Stefano Stacul

Materials 2017, 10(6), 669; https://doi.org/10.3390/ma10060669 - 18 Jun 2017

Cited by 23 | Viewed by 7279

Abstract

Within this paper, the assessment of tension stiffening effects on a reinforced concrete element with the circular sections subjected to axial and bending loads is presented. To this purpose, an enhancement of an analytical model already present within the actual technical literature is [...] Read more.

Within this paper, the assessment of tension stiffening effects on a reinforced concrete element with the circular sections subjected to axial and bending loads is presented. To this purpose, an enhancement of an analytical model already present within the actual technical literature is proposed. The accuracy of the enhanced method is assessed by comparing the experimental results carried out in past research and the numerical ones obtained by the model. Finally, a parametric study is executed in order to study the influence of axial compressive force on the flexural stiffness of reinforced concrete elements that are characterized by a circular section, comparing the secant stiffness evaluated at yielding and at maximum resistance, considering and not considering the effects of tension stiffness. Full article

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Open AccessFeature PaperArticle

New Insights in the Long-Term Atmospheric Corrosion Mechanisms of Low Alloy Steel Reinforcements of Cultural Heritage Buildings

by Marie Bouchar, Philippe Dillmann and Delphine Neff

Materials 2017, 10(6), 670; https://doi.org/10.3390/ma10060670 - 19 Jun 2017

Cited by 12 | Viewed by 5060

Abstract

Reinforcing clamps made of low alloy steel from the Metz cathedral and corroded outdoors during 500 years were studied by OM, FESEM/EDS, and micro-Raman spectroscopy. The corrosion product layer is constituted of a dual structure. The outer layer is mainly constituted of goethite [...] Read more.

Reinforcing clamps made of low alloy steel from the Metz cathedral and corroded outdoors during 500 years were studied by OM, FESEM/EDS, and micro-Raman spectroscopy. The corrosion product layer is constituted of a dual structure. The outer layer is mainly constituted of goethite and lepidocrocite embedding exogenous elements such as Ca and P. The inner layer is mainly constituted of ferrihydrite. The behaviour of the inner layer under conditions simulating the wetting stage of the RH wet/dry atmospheric corrosion cycle was observed by in situ micro-Raman spectroscopy. The disappearance of ferrihydrite near the metal/oxide interface strongly suggests a mechanism of reductive dissolution caused by the oxidation of the metallic substrate and was observed for the first time in situ on an archaeological system. Full article

(This article belongs to the Special Issue Fundamental and Research Frontier of Atmospheric Corrosion)

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Open AccessArticle

Study on Temper Embrittlement and Hydrogen Embrittlement of a Hydrogenation Reactor by Small Punch Test

by Kaishu Guan, Jerzy A. Szpunar, Karel Matocha and Duwei Wang

Materials 2017, 10(6), 671; https://doi.org/10.3390/ma10060671 - 19 Jun 2017

Cited by 15 | Viewed by 6122

Abstract

The study on temper embrittlement and hydrogen embrittlement of a test block from a 3Cr1Mo1/4V hydrogenation reactor after ten years of service was carried out by small punch test (SPT) at different temperatures. The SPT fracture energy E_s_p (derived from integrating [...] Read more.

The study on temper embrittlement and hydrogen embrittlement of a test block from a 3Cr1Mo1/4V hydrogenation reactor after ten years of service was carried out by small punch test (SPT) at different temperatures. The SPT fracture energy E_s_p (derived from integrating the load-displacement curve) divided by the maximum load (F_m) of SPT was used to fit the E_sp/F_m versus-temperature curve to determine the energy transition temperature (T_sp) which corresponded to the ductile-brittle transition temperature of the Charpy impact test. The results indicated that the ratio of E_sp/F_m could better represent the energy of transition in SPT compared with E_sp. The ductile-to-brittle transition temperature of the four different types of materials was measured using the hydrogen charging test by SPT. These four types of materials included the base metal and the weld metal in the as-received state, and the base metal and the weld metal in the de-embrittled state. The results showed that there was a degree of temper embrittlement in the base metal and the weld metal after ten years of service at 390 °C. The specimens became slightly more brittle but this was not obvious after hydrogen charging. Because the toughness of the material of the hydrogenation reactor was very good, the flat samples of SPT could not characterize the energy transition temperature within the liquid nitrogen temperature. Additionally, there was no synergetic effect of temper embrittlement and hydrogen embrittlement found in 3Cr1Mo1/4V steel. Full article

(This article belongs to the Special Issue Selected Papers from SSTT2016)

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Open AccessArticle

The Synthesis of the Core/Shell Structured Diamond/Akageneite Hybrid Particles with Enhanced Polishing Performance

by Jing Lu, Yongchao Xu, Dayu Zhang and Xipeng Xu

Materials 2017, 10(6), 673; https://doi.org/10.3390/ma10060673 - 20 Jun 2017

Cited by 13 | Viewed by 4090

Abstract

In this study, the synthesis of the core/shell structured diamond/akageneite hybrid particles was performed through one-step isothermal hydrolyzing. The hybrid particle was characterized by X-ray diffraction, field emission scanning electron microscopy, and Fourier transform infrared spectra. The test results overall reveal that the [...] Read more.

In this study, the synthesis of the core/shell structured diamond/akageneite hybrid particles was performed through one-step isothermal hydrolyzing. The hybrid particle was characterized by X-ray diffraction, field emission scanning electron microscopy, and Fourier transform infrared spectra. The test results overall reveal that the akageneite coating, phase β-FeO(OH), was uniformly coated onto the diamond surface. The polishing performance of the pristine diamond and hybrid particles for the sapphire substrate was evaluated respectively. The experimental results show that the hybrid particles exhibited improved polishing quality and prolonged effective processing time of polishing pad compared with diamond particles without compromising the material remove rate and surface roughness. The improved polishing behavior might be attributed to the β-FeOOH coating, which is conducive to less abrasive shedding and reducing the scratch depth. Full article

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Open AccessArticle

Material Flow Analysis in Indentation by Two-Dimensional Digital Image Correlation and Finite Elements Method

by Carolina Bermudo, Lorenzo Sevilla and Germán Castillo López

Materials 2017, 10(6), 674; https://doi.org/10.3390/ma10060674 - 21 Jun 2017

Cited by 8 | Viewed by 4554

Abstract

The present work shows the material flow analysis in indentation by the numerical two dimensional Finite Elements (FEM) method and the experimental two-dimensional Digital Image Correlation (DIC) method. To achieve deep indentation without cracking, a ductile material, 99% tin, is used. The results [...] Read more.

The present work shows the material flow analysis in indentation by the numerical two dimensional Finite Elements (FEM) method and the experimental two-dimensional Digital Image Correlation (DIC) method. To achieve deep indentation without cracking, a ductile material, 99% tin, is used. The results obtained from the DIC technique depend predominantly on the pattern conferred to the samples. Due to the absence of a natural pattern, black and white spray painting is used for greater contrast. The stress-strain curve of the material has been obtained and introduced in the Finite Element simulation code used, DEFORM™, allowing for accurate simulations. Two different 2D models have been used: a plain strain model to obtain the load curve and a plain stress model to evaluate the strain maps on the workpiece surface. The indentation displacement load curve has been compared between the FEM and the experimental results, showing a good correlation. Additionally, the strain maps obtained from the material surface with FEM and DIC are compared in order to validate the numerical model. The Von Mises strain results between both of them present a 10–20% difference. The results show that FEM is a good tool for simulating indentation processes, allowing for the evaluation of the maximum forces and deformations involved in the forming process. Additionally, the non-contact DIC technique shows its potential by measuring the superficial strain maps, validating the FEM results. Full article

(This article belongs to the Special Issue Advanced Nanoindentation in Materials)

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4118 KiB

Open AccessArticle

Incipient Fault Detection for Rolling Element Bearings under Varying Speed Conditions

by Lang Xue, Naipeng Li, Yaguo Lei and Ningbo Li

Materials 2017, 10(6), 675; https://doi.org/10.3390/ma10060675 - 20 Jun 2017

Cited by 15 | Viewed by 4313

Abstract

Varying speed conditions bring a huge challenge to incipient fault detection of rolling element bearings because both the change of speed and faults could lead to the amplitude fluctuation of vibration signals. Effective detection methods need to be developed to eliminate the influence [...] Read more.

Varying speed conditions bring a huge challenge to incipient fault detection of rolling element bearings because both the change of speed and faults could lead to the amplitude fluctuation of vibration signals. Effective detection methods need to be developed to eliminate the influence of speed variation. This paper proposes an incipient fault detection method for bearings under varying speed conditions. Firstly, relative residual (RR) features are extracted, which are insensitive to the varying speed conditions and are able to reflect the degradation trend of bearings. Then, a health indicator named selected negative log-likelihood probability (SNLLP) is constructed to fuse a feature set including RR features and non-dimensional features. Finally, based on the constructed SNLLP health indicator, a novel alarm trigger mechanism is designed to detect the incipient fault. The proposed method is demonstrated using vibration signals from bearing tests and industrial wind turbines. The results verify the effectiveness of the proposed method for incipient fault detection of rolling element bearings under varying speed conditions. Full article

(This article belongs to the Special Issue Structural Health Monitoring for Aerospace Applications 2017)

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Open AccessCommunication

Temperature and Copper Concentration Effects on the Formation of Graphene-Encapsulated Copper Nanoparticles from Kraft Lignin

by Weiqi Leng, H. Michael Barnes, Zhiyong Cai and Jilei Zhang

Materials 2017, 10(6), 677; https://doi.org/10.3390/ma10060677 - 21 Jun 2017

Cited by 9 | Viewed by 4247

Abstract

The effects of temperature and copper catalyst concentration on the formation of graphene-encapsulated copper nanoparticles (GECNs) were investigated by means of X-ray diffraction, Fourier transform infrared spectroscopy-attenuated total reflectance, and transmission electron microscopy. Results showed that higher amounts of copper atoms facilitated the [...] Read more.

The effects of temperature and copper catalyst concentration on the formation of graphene-encapsulated copper nanoparticles (GECNs) were investigated by means of X-ray diffraction, Fourier transform infrared spectroscopy-attenuated total reflectance, and transmission electron microscopy. Results showed that higher amounts of copper atoms facilitated the growth of more graphene islands and formed smaller size GECNs. A copper catalyst facilitated the decomposition of lignin at the lowest temperature studied (600 °C). Increasing the temperature up to 1000 °C retarded the degradation process, while assisting the reconfiguration of the defective sites of the graphene layers, thus producing higher-quality GECNs. Full article

(This article belongs to the Section Advanced Composites)

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3640 KiB

Open AccessArticle

Ternary CNTs@TiO₂/CoO Nanotube Composites: Improved Anode Materials for High Performance Lithium Ion Batteries

by Mahmoud Madian, Raghunandan Ummethala, Ahmed Osama Abo El Naga, Nahla Ismail, Mark Hermann Rümmeli, Alexander Eychmüller and Lars Giebeler

Materials 2017, 10(6), 678; https://doi.org/10.3390/ma10060678 - 20 Jun 2017

Cited by 18 | Viewed by 6051

Abstract

TiO₂ nanotubes (NTs) synthesized by electrochemical anodization are discussed as very promising anodes for lithium ion batteries, owing to their high structural stability, high surface area, safety, and low production cost. However, their poor electronic conductivity and low Li⁺ ion diffusivity [...] Read more.

TiO₂ nanotubes (NTs) synthesized by electrochemical anodization are discussed as very promising anodes for lithium ion batteries, owing to their high structural stability, high surface area, safety, and low production cost. However, their poor electronic conductivity and low Li⁺ ion diffusivity are the main drawbacks that prevent them from achieving high electrochemical performance. Herein, we report the fabrication of a novel ternary carbon nanotubes (CNTs)@TiO₂/CoO nanotubes composite by a two-step synthesis method. The preparation includes an initial anodic fabrication of well-ordered TiO₂/CoO NTs from a Ti-Co alloy, followed by growing of CNTs horizontally on the top of the oxide films using a simple spray pyrolysis technique. The unique 1D structure of such a hybrid nanostructure with the inclusion of CNTs demonstrates significantly enhanced areal capacity and rate performances compared to pure TiO₂ and TiO₂/CoO NTs, without CNTs tested under identical conditions. The findings reveal that CNTs provide a highly conductive network that improves Li⁺ ion diffusivity, promoting a strongly favored lithium insertion into the TiO₂/CoO NT framework, and hence resulting in high capacity and an extremely reproducible high rate capability. Full article

(This article belongs to the Special Issue Advances in Renewable Energy Conversion Materials)

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8610 KiB

Open AccessArticle

Effect of Carbon in Fabrication Al-SiC Nanocomposites for Tribological Application

by Bartosz Hekner, Jerzy Myalski, Tomasz Pawlik and Małgorzata Sopicka-Lizer

Materials 2017, 10(6), 679; https://doi.org/10.3390/ma10060679 - 21 Jun 2017

Cited by 23 | Viewed by 5314

Abstract

Aluminium-based hybrid composites are a new class of advanced materials with the potential of satisfying the demands in engineering applications. This paper describes the effects of carbon addition on the formation and properties of AMC with SiC nanoparticles reinforcement. The composites were produced [...] Read more.

Aluminium-based hybrid composites are a new class of advanced materials with the potential of satisfying the demands in engineering applications. This paper describes the effects of carbon addition on the formation and properties of AMC with SiC nanoparticles reinforcement. The composites were produced via mechanical alloying followed by hot pressing. Three forms of carbon, graphite (GR), multiwalled carbon nanotubes (CNTs), and, for the first time, glassy carbon (GC), were used for the hybrid composites manufacturing and compared with tribological properties of Al-SiC composite without carbon addition. GC and CNTs enhanced formation of Al-SiC composite particles and resulted in a homogeneous distribution of reinforcing particles. On the other hand, GR addition altered mechanochemical alloying and did not lead to a proper distribution of nanoparticulate SiC reinforcement. Hot pressing technique led to the reaction between Al and carbon as well as SiC particles and caused the formation of Al₄C₃ and γ-Al₂O₃. The subsistence of carbon particles in the composites altered the predominant wear mechanisms since the wear reduction and the stabilization of the friction coefficient were observed. GC with simultaneous γ-Al₂O₃ formation in the hybrid Al-SiC(n)-C composites turned out to be the most effective additive in terms of their tribological behaviour. Full article

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1722 KiB

Open AccessFeature PaperArticle

Bias Stress and Temperature Impact on InGaZnO TFTs and Circuits

by Jorge Martins, Pydi Bahubalindruni, Ana Rovisco, Asal Kiazadeh, Rodrigo Martins, Elvira Fortunato and Pedro Barquinha

Materials 2017, 10(6), 680; https://doi.org/10.3390/ma10060680 - 21 Jun 2017

Cited by 24 | Viewed by 5931

Abstract

This paper focuses on the analysis of InGaZnO thin-film transistors (TFTs) and circuits under the influence of different temperatures and bias stress, shedding light into their robustness when used in real-world applications. For temperature-dependent measurements, a temperature range of 15 to 85 °C [...] Read more.

This paper focuses on the analysis of InGaZnO thin-film transistors (TFTs) and circuits under the influence of different temperatures and bias stress, shedding light into their robustness when used in real-world applications. For temperature-dependent measurements, a temperature range of 15 to 85 °C was considered. In case of bias stress, both gate and drain bias were applied for 60 min. Though isolated transistors show a variation of drain current as high as 56% and 172% during bias voltage and temperature stress, the employed circuits were able to counteract it. Inverters and two-TFT current mirrors following simple circuit topologies showed a gain variation below 8%, while the improved robustness of a cascode current mirror design is proven by showing a gain variation less than 5%. The demonstration that the proper selection of TFT materials and circuit topologies results in robust operation of oxide electronics under different stress conditions and over a reasonable range of temperatures proves that the technology is suitable for applications such as smart food packaging and wearables. Full article

(This article belongs to the Special Issue Oxide Semiconductor Thin-Film Transistor)

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8883 KiB

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Ultrasonic Measurements on β Cyclodextrin/Hydroxyapatite Composites for Potential Water Depollution

by Daniela Predoi, Mihai Valentin Predoi, Simona Liliana Iconaru, Moncef Ech Cherif El Kettani, Damien Leduc and Alina Mihaela Prodan

Materials 2017, 10(6), 681; https://doi.org/10.3390/ma10060681 - 21 Jun 2017

Cited by 14 | Viewed by 4756

Abstract

This paper presents structural, morphological and preliminary ultrasonic characterizations of the β-Cyclodextrin/hydroxyapatite (CD-HAp) composites synthesized by an adapted co-precipitation method. The structural and morphological properties were evaluated by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX). The specific surface area, pore [...] Read more.

This paper presents structural, morphological and preliminary ultrasonic characterizations of the β-Cyclodextrin/hydroxyapatite (CD-HAp) composites synthesized by an adapted co-precipitation method. The structural and morphological properties were evaluated by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX). The specific surface area, pore size and pore volume were determined using the methods of Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH), respectively. The novelty of our study consists in preliminary ultrasonic measurements conducted on CD-HAp composite, uniformly dispersed in distilled water. The benefit of this non-destructive method was to facilitate and simplify the characterization techniques of nanoparticles. Our experiments proved that the efficiency of lead ion removal by CD-HAp composites depended on the initial concentration of lead. The maximum adsorption capacity of the solid phase, for Pb²⁺ indicated a higher rate of removal by the CD-HAp_2. These adsorption results bring valuable insight into the beneficial contribution of our compounds, for the removal of heavy metal ions from aqueous solutions. Furthermore, in the present study, was evaluated the toxic effect of lead ions adsorbed by hydroxyapatite from contaminated water on HeLa cells. Full article

(This article belongs to the Special Issue Sorption Materials for Environment Purification)

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2475 KiB

Open AccessArticle

Improving Sorbents for Glycerol Capture in Biodiesel Refinement

by Brandy J. Johnson, Brian J. Melde, Martin H. Moore, Anthony P. Malanoski and Jenna R. Taft

Materials 2017, 10(6), 682; https://doi.org/10.3390/ma10060682 - 21 Jun 2017

Cited by 5 | Viewed by 3726

Abstract

Biodiesel is produced by transesterification of animal fat, vegetable oil, or waste cooking oil with alcohol. After production costs, the economic viability of biodiesel is dependent on what steps are necessary to remove impurities following synthesis and the effectiveness of quality control analysis. [...] Read more.

Biodiesel is produced by transesterification of animal fat, vegetable oil, or waste cooking oil with alcohol. After production costs, the economic viability of biodiesel is dependent on what steps are necessary to remove impurities following synthesis and the effectiveness of quality control analysis. Solid-phase extraction offers a potentially advantageous approach in biodiesel processing applications. Nanoporous scaffolds were investigated for adsorption of glycerol, a side product of biodiesel synthesis that is detrimental to engine combustion when present. Materials were synthesized with varying pore wall composition, including ethane and diethylbenzene bridging groups, and sulfonated to promote hydrogen bonding interactions with glycerol. Materials bearing sulfonate groups throughout the scaffold walls as well as those post-synthetically grafted onto the surfaces show notably superior performance for uptake of glycerol. The sorbents are effective when used in biodiesel mixtures, removing greater than 90% of glycerol from a biodiesel preparation. Full article

(This article belongs to the Section Porous Materials)

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2061 KiB

Open AccessArticle

Experimental and Theoretical Modal Analysis of Full-Sized Wood Composite Panels Supported on Four Nodes

by Cheng Guan, Houjiang Zhang, Xiping Wang, Hu Miao, Lujing Zhou and Fenglu Liu

Materials 2017, 10(6), 683; https://doi.org/10.3390/ma10060683 - 21 Jun 2017

Cited by 23 | Viewed by 5678

Abstract

Key elastic properties of full-sized wood composite panels (WCPs) must be accurately determined not only for safety, but also serviceability demands. In this study, the modal parameters of full-sized WCPs supported on four nodes were analyzed for determining the modulus of elasticity ( [...] Read more.

Key elastic properties of full-sized wood composite panels (WCPs) must be accurately determined not only for safety, but also serviceability demands. In this study, the modal parameters of full-sized WCPs supported on four nodes were analyzed for determining the modulus of elasticity (E) in both major and minor axes, as well as the in-plane shear modulus of panels by using a vibration testing method. The experimental modal analysis was conducted on three full-sized medium-density fiberboard (MDF) and three full-sized particleboard (PB) panels of three different thicknesses (12, 15, and 18 mm). The natural frequencies and mode shapes of the first nine modes of vibration were determined. Results from experimental modal testing were compared with the results of a theoretical modal analysis. A sensitivity analysis was performed to identify the sensitive modes for calculating E (major axis: E_x and minor axis: E_y) and the in-plane shear modulus (G_xy) of the panels. Mode shapes of the MDF and PB panels obtained from modal testing are in a good agreement with those from theoretical modal analyses. A strong linear relationship exists between the measured natural frequencies and the calculated frequencies. The frequencies of modes (2, 0), (0, 2), and (2, 1) under the four-node support condition were determined as the characteristic frequencies for calculation of E_x, E_y, and G_xy of full-sized WCPs. The results of this study indicate that the four-node support can be used in free vibration test to determine the elastic properties of full-sized WCPs. Full article

(This article belongs to the Special Issue Modeling and Simulation of Advanced Composite Materials)

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Review

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Open AccessFeature PaperReview

Micro-Mechanical Response of an Al-Mg Hybrid System Synthesized by High-Pressure Torsion

by Megumi Kawasaki and Jae-il Jang

Materials 2017, 10(6), 596; https://doi.org/10.3390/ma10060596 - 30 May 2017

Cited by 23 | Viewed by 4867

Abstract

This paper summarizes recent efforts to evaluate the potential for the formation of a metal matrix nanocomposite (MMNC) by processing two commercial bulk metals of aluminum and magnesium alloy through high-pressure torsion (HPT) at room temperature. After significant evolutions in microstructures, successful fabrication [...] Read more.

This paper summarizes recent efforts to evaluate the potential for the formation of a metal matrix nanocomposite (MMNC) by processing two commercial bulk metals of aluminum and magnesium alloy through high-pressure torsion (HPT) at room temperature. After significant evolutions in microstructures, successful fabrication of an Al-Mg hybrid system was demonstrated by observing unique microstructures consisting of a multi-layered structure and MMNC. Moreover, the evolution of small-scale mechanical properties was examined through the novel technique of nanoindentation and the improvement in plasticity was estimated by calculating the strain rate sensitivity of the Al-Mg hybrid system after HPT. The present paper demonstrates that, in addition to conventional tensile testing, the nanoindentation technique is exceptionally promising for ultrafine-grained materials processed by HPT, where the samples may have small overall dimensions and include heterogeneity in the microstructure. Full article

(This article belongs to the Special Issue Advanced Nanoindentation in Materials)

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4363 KiB

Open AccessReview

Chitosan Biomaterials for Current and Potential Dental Applications

by Shehriar Husain, Khalid H. Al-Samadani, Shariq Najeeb, Muhammad S. Zafar, Zohaib Khurshid, Sana Zohaib and Saad B. Qasim

Materials 2017, 10(6), 602; https://doi.org/10.3390/ma10060602 - 31 May 2017

Cited by 163 | Viewed by 13044

Abstract

Chitosan (CHS) is a very versatile natural biomaterial that has been explored for a range of bio-dental applications. CHS has numerous favourable properties such as biocompatibility, hydrophilicity, biodegradability, and a broad antibacterial spectrum (covering gram-negative and gram-positive bacteria as well as fungi). In [...] Read more.

Chitosan (CHS) is a very versatile natural biomaterial that has been explored for a range of bio-dental applications. CHS has numerous favourable properties such as biocompatibility, hydrophilicity, biodegradability, and a broad antibacterial spectrum (covering gram-negative and gram-positive bacteria as well as fungi). In addition, the molecular structure boasts reactive functional groups that provide numerous reaction sites and opportunities for forging electrochemical relationships at the cellular and molecular levels. The unique properties of CHS have attracted materials scientists around the globe to explore it for bio-dental applications. This review aims to highlight and discuss the hype around the development of novel chitosan biomaterials. Utilizing chitosan as a critical additive for the modification and improvement of existing dental materials has also been discussed. Full article

(This article belongs to the Section Biomaterials)

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Open AccessReview

Advances in Photocatalytic CO₂ Reduction with Water: A Review

by Samsun Nahar, M. F. M. Zain, Abdul Amir H. Kadhum, Hassimi Abu Hasan and Md. Riad Hasan

Materials 2017, 10(6), 629; https://doi.org/10.3390/ma10060629 - 8 Jun 2017

Cited by 195 | Viewed by 20962

Abstract

In recent years, the increasing level of CO₂ in the atmosphere has not only contributed to global warming but has also triggered considerable interest in photocatalytic reduction of CO₂. The reduction of CO₂ with H₂O using sunlight [...] Read more.

In recent years, the increasing level of CO₂ in the atmosphere has not only contributed to global warming but has also triggered considerable interest in photocatalytic reduction of CO₂. The reduction of CO₂ with H₂O using sunlight is an innovative way to solve the current growing environmental challenges. This paper reviews the basic principles of photocatalysis and photocatalytic CO₂ reduction, discusses the measures of the photocatalytic efficiency and summarizes current advances in the exploration of this technology using different types of semiconductor photocatalysts, such as TiO₂ and modified TiO₂, layered-perovskite Ag/ALa₄Ti₄O₁₅ (A = Ca, Ba, Sr), ferroelectric LiNbO₃, and plasmonic photocatalysts. Visible light harvesting, novel plasmonic photocatalysts offer potential solutions for some of the main drawbacks in this reduction process. Effective plasmonic photocatalysts that have shown reduction activities towards CO₂ with H₂O are highlighted here. Although this technology is still at an embryonic stage, further studies with standard theoretical and comprehensive format are suggested to develop photocatalysts with high production rates and selectivity. Based on the collected results, the immense prospects and opportunities that exist in this technique are also reviewed here. Full article

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452 KiB

Open AccessReview

Additive Manufacturing Processes: Selective Laser Melting, Electron Beam Melting and Binder Jetting—Selection Guidelines

by Prashanth Konda Gokuldoss, Sri Kolla and Jürgen Eckert

Materials 2017, 10(6), 672; https://doi.org/10.3390/ma10060672 - 19 Jun 2017

Cited by 572 | Viewed by 28479

Abstract

Additive manufacturing (AM), also known as 3D printing or rapid prototyping, is gaining increasing attention due to its ability to produce parts with added functionality and increased complexities in geometrical design, on top of the fact that it is theoretically possible to produce [...] Read more.

Additive manufacturing (AM), also known as 3D printing or rapid prototyping, is gaining increasing attention due to its ability to produce parts with added functionality and increased complexities in geometrical design, on top of the fact that it is theoretically possible to produce any shape without limitations. However, most of the research on additive manufacturing techniques are focused on the development of materials/process parameters/products design with different additive manufacturing processes such as selective laser melting, electron beam melting, or binder jetting. However, we do not have any guidelines that discuss the selection of the most suitable additive manufacturing process, depending on the material to be processed, the complexity of the parts to be produced, or the design considerations. Considering the very fact that no reports deal with this process selection, the present manuscript aims to discuss the different selection criteria that are to be considered, in order to select the best AM process (binder jetting/selective laser melting/electron beam melting) for fabricating a specific component with a defined set of material properties. Full article

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10532 KiB

Open AccessReview

Binary Phase Diagrams and Thermodynamic Properties of Silicon and Essential Doping Elements (Al, As, B, Bi, Ga, In, N, P, Sb and Tl)

by Ahmad Mostafa and Mamoun Medraj

Materials 2017, 10(6), 676; https://doi.org/10.3390/ma10060676 - 20 Jun 2017

Cited by 60 | Viewed by 19778

Abstract

Fabrication of solar and electronic silicon wafers involves direct contact between solid, liquid and gas phases at near equilibrium conditions. Understanding of the phase diagrams and thermochemical properties of the Si-dopant binary systems is essential for providing processing conditions and for understanding the [...] Read more.

Fabrication of solar and electronic silicon wafers involves direct contact between solid, liquid and gas phases at near equilibrium conditions. Understanding of the phase diagrams and thermochemical properties of the Si-dopant binary systems is essential for providing processing conditions and for understanding the phase formation and transformation. In this work, ten Si-based binary phase diagrams, including Si with group IIIA elements (Al, B, Ga, In and Tl) and with group VA elements (As, Bi, N, P and Sb), have been reviewed. Each of these systems has been critically discussed on both aspects of phase diagram and thermodynamic properties. The available experimental data and thermodynamic parameters in the literature have been summarized and assessed thoroughly to provide consistent understanding of each system. Some systems were re-calculated to obtain a combination of the best evaluated phase diagram and a set of optimized thermodynamic parameters. As doping levels of solar and electronic silicon are of high technological importance, diffusion data has been presented to serve as a useful reference on the properties, behavior and quantities of metal impurities in silicon. This paper is meant to bridge the theoretical understanding of phase diagrams with the research and development of solar-grade silicon production, relying on the available information in the literature and our own analysis. Full article

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