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Materials, Volume 12, Issue 1 (January-1 2019)

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Cover Story (view full-size image) MD simulations were employed to study the He effects on generation and growth of cracks in [...] Read more.
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Open AccessArticle Cu-Doped ZnO Electronic Structure and Optical Properties Studied by First-Principles Calculations and Experiments
Materials 2019, 12(1), 196; https://doi.org/10.3390/ma12010196
Received: 8 November 2018 / Revised: 29 December 2018 / Accepted: 4 January 2019 / Published: 8 January 2019
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Abstract
The band structure, the density of states and optical absorption properties of Cu-doped ZnO were studied by the first-principles generalized gradient approximation plane-wave pseudopotential method based on density functional theory. For the Zn1-xCuxO (x = 0, x [...] Read more.
The band structure, the density of states and optical absorption properties of Cu-doped ZnO were studied by the first-principles generalized gradient approximation plane-wave pseudopotential method based on density functional theory. For the Zn1-xCuxO (x = 0, x = 0.0278, x = 0.0417) original structure, geometric optimization and energy calculations were performed and compared with experimental results. With increasing Cu concentration, the band gap of the Zn1-xCuxO decreased due to the shift of the conduction band. Since the impurity level was introduced after Cu doping, the conduction band was moved downwards. Additionally, it was shown that the insertion of a Cu atom leads to a red shift of the optical absorption edge, which was consistent with the experimental results. Full article
(This article belongs to the Special Issue Advanced Thermoelectric Materials)
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Open AccessArticle Pro-Degradant Activity of Naturally Occurring Compounds on Polyethylene in Accelerate Weathering Conditions
Materials 2019, 12(1), 195; https://doi.org/10.3390/ma12010195
Received: 30 November 2018 / Revised: 28 December 2018 / Accepted: 4 January 2019 / Published: 8 January 2019
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Abstract
In this work, naturally occurring compounds, such as Vitamin E (VE) and Ferulic Acid (FA), at high concentrations, have been considered as pro-degradant agents for Low Density Polyethylene (PE). However, all obtained results using the naturally occurring molecules as pro-oxidant agents for PE [...] Read more.
In this work, naturally occurring compounds, such as Vitamin E (VE) and Ferulic Acid (FA), at high concentrations, have been considered as pro-degradant agents for Low Density Polyethylene (PE). However, all obtained results using the naturally occurring molecules as pro-oxidant agents for PE have been compared with the results achieved using a classical pro-oxidant agent, such as calcium stearate (Ca stearate) and with neat PE. The preliminary characterization, through rheological, mechanical and thermal analysis, of the PE-based systems highlights that the used naturally occurring molecules are able to exert a slight plasticizing action on PE and subsequently the PE rigidity and crystallinity slightly decrease, while the ductility increases. To assess the pro-degradant activity of the considered naturally occurring compounds, thin films of neat PE and PE-based systems containing 2 and 3 wt.% Ca stearate, VE and FA have been produced and subjected to accelerated weathering upon UVB light exposure. All obtained results point out that the VE and FA, at these high concentrations, exert a clear pro-oxidant activity in PE and this pro-oxidant activity is very similar to that exerted by Ca stearate. Moreover, the VE and FA at high concentrations can be considered as suitable eco-friendly pro-degradant additives for PE, also in order to control the polyolefin degradation times. Full article
(This article belongs to the Special Issue Durability and Life time of Polymers, Composites and Nanocomposites)
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Open AccessEditorial Acknowledgement to Reviewers of Materials in 2018
Materials 2019, 12(1), 194; https://doi.org/10.3390/ma12010194
Published: 8 January 2019
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Abstract
Rigorous peer-review is the corner-stone of high-quality academic publishing[...] Full article
Open AccessArticle Design, Electron Transfer Process, and Opto-Electronic Property of Solar Cell Using Triphenylamine-Based D-π-A Architectures
Materials 2019, 12(1), 193; https://doi.org/10.3390/ma12010193
Received: 29 November 2018 / Revised: 23 December 2018 / Accepted: 28 December 2018 / Published: 8 January 2019
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Abstract
A series of D-π-A type dyes were designed based on the experimentally synthesized A1 by introducing different functional groups on the donor and π-spacer, and the optical and electrical properties were calculated by using density functional theory (DFT) and time-dependent DFT (TD-DFT). P1–P6 [...] Read more.
A series of D-π-A type dyes were designed based on the experimentally synthesized A1 by introducing different functional groups on the donor and π-spacer, and the optical and electrical properties were calculated by using density functional theory (DFT) and time-dependent DFT (TD-DFT). P1–P6 present highest light harvesting efficiency (LHE), driving force of electron injection ( Δ G i n j e c t ), reorganization energy ( Δ G r e g ) and e V O C . These critical parameters have a close relationship with the short-circuit current density ( J S C ) and open-circuit photovoltage ( V O C ), and lead to P1–P6 will exhibit higher efficiency. D4 also exhibit superior properties in the driving force of electron injection ( Δ G i n j e c t ), reorganization energy ( Δ G r e g ), which will lead to a higher short-circuit current density ( J S C ). We hope that these results will be helpful for experiments to synthesize new and highly efficient dyes. Full article
(This article belongs to the Special Issue Interface Engineering in Organic/Inorganic Hybrid Solar Cells)
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Open AccessArticle Effect of Hydration and Carbonation Progress on the Porosity and Permeability of Cement Pastes
Materials 2019, 12(1), 192; https://doi.org/10.3390/ma12010192
Received: 11 December 2018 / Revised: 28 December 2018 / Accepted: 3 January 2019 / Published: 8 January 2019
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Abstract
This paper presents the results of comprehensive cement paste porosity and gas permeability tests. The tests conducted concerned ordinary Portland cement (OPC) cement pastes with varying water-cement ratios ranging from 0.3 to 0.6. The tests were conducted after the curing of cement paste [...] Read more.
This paper presents the results of comprehensive cement paste porosity and gas permeability tests. The tests conducted concerned ordinary Portland cement (OPC) cement pastes with varying water-cement ratios ranging from 0.3 to 0.6. The tests were conducted after the curing of cement paste for 90 days and two years under laboratory conditions. Open porosity was determined using three methods: helium pycnometry, mercury intrusion porosimetry, and water saturation. Permeability was determined using a modified RILEM-Cembureau method. The results obtained demonstrated that permeability does not change significantly over time despite the observed material shifts in open porosity characteristics caused both by further progress in hydration and by the carbonation process that occurs. The results of the tests conducted also permitted the quantitative determination of the impact of the water-cement ratio, age, and the progress of carbonation on open porosity measured using different methods and also on the gas permeability of the pastes. Full article
(This article belongs to the Section Porous Materials)
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Open AccessReview Perspective on Plasma Polymers for Applied Biomaterials Nanoengineering and the Recent Rise of Oxazolines
Materials 2019, 12(1), 191; https://doi.org/10.3390/ma12010191
Received: 3 December 2018 / Revised: 21 December 2018 / Accepted: 2 January 2019 / Published: 8 January 2019
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Abstract
Plasma polymers are unconventional organic thin films which only partially share the properties traditionally attributed to polymeric materials. For instance, they do not consist of repeating monomer units but rather present a highly crosslinked structure resembling the chemistry of the precursor used for [...] Read more.
Plasma polymers are unconventional organic thin films which only partially share the properties traditionally attributed to polymeric materials. For instance, they do not consist of repeating monomer units but rather present a highly crosslinked structure resembling the chemistry of the precursor used for deposition. Due to the complex nature of the deposition process, plasma polymers have historically been produced with little control over the chemistry of the plasma phase which is still poorly understood. Yet, plasma polymer research is thriving, in par with the commercialisation of innumerable products using this technology, in fields ranging from biomedical to green energy industries. Here, we briefly summarise the principles at the basis of plasma deposition and highlight recent progress made in understanding the unique chemistry and reactivity of these films. We then demonstrate how carefully designed plasma polymer films can serve the purpose of fundamental research and biomedical applications. We finish the review with a focus on a relatively new class of plasma polymers which are derived from oxazoline-based precursors. This type of coating has attracted significant attention recently due to its unique properties. Full article
(This article belongs to the Special Issue Plasma Polymerized Materials)
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Open AccessArticle Minority Carrier Lifetime Measurements for Contactless Oxidation Process Characterization and Furnace Profiling
Materials 2019, 12(1), 190; https://doi.org/10.3390/ma12010190
Received: 30 November 2018 / Revised: 24 December 2018 / Accepted: 2 January 2019 / Published: 8 January 2019
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Abstract
Contactless minority carrier lifetime (lifetime) measurements by means of microwave detected photoconductivity are employed for oxidation process characterization and furnace profiling. Characterization is performed on oxidized float zone substrates with high resistivity and outstanding bulk quality, suggesting that the measured effective lifetime is [...] Read more.
Contactless minority carrier lifetime (lifetime) measurements by means of microwave detected photoconductivity are employed for oxidation process characterization and furnace profiling. Characterization is performed on oxidized float zone substrates with high resistivity and outstanding bulk quality, suggesting that the measured effective lifetime is strongly dominated by interface recombination and therefore reflects the oxide quality. The applied approach requires neither test structures nor time consuming measurements and is therefore of particular interest if high throughput is required. The method is used to investigate the impact of oxidation furnace leakage as well as to analyze the oxidation homogeneity across a horizontal oxidation furnace. For comparison, capacitance-voltage measurements are conducted to characterize the oxide properties. It is found that any type of furnace leakage, which induces fixed oxide charges as well as interface states, has a heavy impact on the measured effective lifetime, especially on the shape of generation rate dependent lifetime curves. Furthermore, a distinct lifetime decrease towards the tube door of the oxidation furnace could be observed. The latter is even detectable in an ideal oxidation process, generating high quality oxides. Besides plain equipment characterization, the presented approach is suitable to optimize the oxidation process itself regarding different parameters like temperature, gas flow, pressure, or process time. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessArticle Green Biosynthesis of Silver Nanoparticles Using Eriobotrya japonica (Thunb.) Leaf Extract for Reductive Catalysis
Materials 2019, 12(1), 189; https://doi.org/10.3390/ma12010189
Received: 30 November 2018 / Revised: 28 December 2018 / Accepted: 31 December 2018 / Published: 8 January 2019
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Abstract
This article reports on silver nanoparticles (AgNPs) that were green-synthesized by using Eriobotrya japonica (Thunb.) leaf extract and their use for the catalytic degradation of reactive dyes. The properties of biogenic AgNPs were characterized using UV-vis absorption spectroscopy, field emission scanning electron microscope [...] Read more.
This article reports on silver nanoparticles (AgNPs) that were green-synthesized by using Eriobotrya japonica (Thunb.) leaf extract and their use for the catalytic degradation of reactive dyes. The properties of biogenic AgNPs were characterized using UV-vis absorption spectroscopy, field emission scanning electron microscope (FESEM), X-ray powder diffraction (XRD), transmission electron microscope (TEM), Fourier transforming infrared spectroscopy (FTIR), energy dispersive X-ray spectroscopy (EDS), and selected area electron diffraction (SAED) analysis. The UV-vis spectroscopy and X-ray analyses confirmed the formation of AgNPs and showed the strong absorbance around 467 nm with surface plasmon resonance (SPR). The mean diameter of biogenic AgNPs at room (20 °C), moderate (50 °C), and high temperatures (80 °C) were 9.26 ± 2.72, 13.09 ± 3.66, and 17.28 ± 5.78 nm, respectively. The reaction temperature had significant impacts on the sizes of synthesized AgNPs. The higher the synthesis temperature, the larger size and the lower catalysis activity for reductive decomposition of reactive dyes via NaBH4. The results supported a bio-green approach for developing AgNPs with a small size and stable degradation activity of reactive dyes over 92% in 30 min by using Eriobotrya japonica (Thunb.) leaf extract at pH 7, 20 °C, and 1:10 ratio of silver nitrate added to the leaf extract. Full article
(This article belongs to the Special Issue Advanced Functional Nanomaterials and Their Applications)
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Open AccessArticle Three-Dimensional Porous Ti3C2Tx-NiO Composite Electrodes with Enhanced Electrochemical Performance for Supercapacitors
Materials 2019, 12(1), 188; https://doi.org/10.3390/ma12010188
Received: 5 December 2018 / Revised: 26 December 2018 / Accepted: 28 December 2018 / Published: 8 January 2019
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Abstract
Ti3C2Tx and Ti3C2Tx-NiO composites with three-dimensional (3D) porous networks were successfully fabricated via vacuum freeze-drying. The microstructure, absorption, and electrochemical properties of the developed composites were investigated. Nickel oxide (NiO) nanoparticles could [...] Read more.
Ti3C2Tx and Ti3C2Tx-NiO composites with three-dimensional (3D) porous networks were successfully fabricated via vacuum freeze-drying. The microstructure, absorption, and electrochemical properties of the developed composites were investigated. Nickel oxide (NiO) nanoparticles could be evenly distributed on the three-dimensional network of three-dimensional Ti3C2Tx using solution processing. When employed as electrochemical capacitor electrodes in 1 M environmentally friendly sodium sulfate, Na2SO4, solution, the three-dimensional porous Ti3C2Tx-NiO composite electrodes exhibited considerable volume specific capacitance as compared to three-dimensional porous Ti3C2Tx. The three-dimensional porous Ti3C2Tx-NiO composite delivered a remarkable cycling performance with a capacitance retention of up to 114% over 2500 cycles. The growth trend of the capacitance with NiO content shows that nickel oxide plays a crucial role in the composite electrodes. These results present a roadmap for the development of convenient and economical supercapacitors in consideration with the possibilities of morphological control and the extensibility of the process. Full article
(This article belongs to the Special Issue MAX Phases and MXenes: Synthesis and Applications)
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Open AccessArticle Soft and Stiff Simplex Tensegrity Lattices as Extreme Smart Metamaterials
Materials 2019, 12(1), 187; https://doi.org/10.3390/ma12010187
Received: 9 November 2018 / Revised: 23 December 2018 / Accepted: 3 January 2019 / Published: 8 January 2019
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Abstract
The present paper is dedicated to an evaluation of novel cellular metamaterials based on a tensegrity pattern. The materials are constructed from supercells, each of which consists of a number of simplex modules with different geometrical proportions. Mechanical properties of the metamaterial can [...] Read more.
The present paper is dedicated to an evaluation of novel cellular metamaterials based on a tensegrity pattern. The materials are constructed from supercells, each of which consists of a number of simplex modules with different geometrical proportions. Mechanical properties of the metamaterial can be controlled by adjusting the level of self-equilibrated forces or by changing the properties of structural members. A continuum model based on the equivalence of strain energy of the 3D theory of elasticity with a discrete formulation is used to identify the qualitative properties of the considered metamaterials. The model allows the inclusion of nonlinearities related to the equations of equilibrium in actual configuration of the structure with self-equilibrated set of normal forces typical for tensegrities. The lattices are recognised as extreme metamaterials according to the eigensolution of the equivalent elasticity matrices of the continuum model. The six representative deformation modes are defined and discussed: stiff, soft and medium extensional modes and high (double) as well as low shear modes. The lattices are identified as unimode or nearly bimode according to the classification of extreme materials. Full article
(This article belongs to the Special Issue New Horizon of Plasmonics and Metamaterials)
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Open AccessFeature PaperArticle Comparative Study of Physicochemical and Antibacterial Properties of ZnO Nanoparticles Prepared by Laser Ablation of Zn Target in Water and Air
Materials 2019, 12(1), 186; https://doi.org/10.3390/ma12010186
Received: 7 December 2018 / Revised: 30 December 2018 / Accepted: 3 January 2019 / Published: 8 January 2019
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Abstract
Here, we report on ZnO nanoparticles (NPs) generated by nanosecond pulsed laser (Nd:YAG, 1064 nm) through ablation of metallic Zn target in water and air and their comparative analysis as potential nanomaterials for biomedical applications. The prepared nanomaterials were carefully characterized in terms [...] Read more.
Here, we report on ZnO nanoparticles (NPs) generated by nanosecond pulsed laser (Nd:YAG, 1064 nm) through ablation of metallic Zn target in water and air and their comparative analysis as potential nanomaterials for biomedical applications. The prepared nanomaterials were carefully characterized in terms of their structure, composition, morphology and defects. It was found that in addition to the main wurtzite ZnO phase, which is conventionally prepared and reported by others, the sample laser generated in air also contained some amount of monoclinic zinc hydroxynitrate. Both nanomaterials were then used to modify model wound dressings based on biodegradable poly l-lactic acid. The as-prepared model dressings were tested as biomedical materials with bactericidal properties towards S. aureus and E. coli strains. The advantages of the NPs prepared in air over their counterparts generated in water found in this work are discussed. Full article
(This article belongs to the Special Issue Laser Ablation in the Synthesis of Novel Nanostructured Materials)
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Open AccessArticle Control over the Percentage, Shape and Size of the Graphite Particles in Martensitic White Castings Alloyed with Cr, Nb and Mg
Materials 2019, 12(1), 185; https://doi.org/10.3390/ma12010185
Received: 11 December 2018 / Revised: 28 December 2018 / Accepted: 29 December 2018 / Published: 8 January 2019
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This paper presents the results obtained regarding the control by manufacturers of the percentage, shape, and size of the precipitated graphite in the working layer of duplex work-rolls used in hot strip mill finishing stands. This working layer is manufactured in a martensitic [...] Read more.
This paper presents the results obtained regarding the control by manufacturers of the percentage, shape, and size of the precipitated graphite in the working layer of duplex work-rolls used in hot strip mill finishing stands. This working layer is manufactured in a martensitic white cast iron alloyed with Cr and Nb to promote the precipitation of M3C and MC carbides, which provide a high wear resistance. The thermal cycling behavior of this layer also has a decisive influence on its service life. In this context, the percentage of graphite and its morphology play a very important role against said thermal cycling. With the aim of studying their effect on the sphericity of graphite, the analyzed industrial manufacturing factors worth highlighting include the liquidus temperature, the %Si, the use of an FeSi inoculant with traces of Lanthanum, inoculation with different amounts of FeB and SiCaMn, and the addition of Mg. At the periphery of the working layer, it was found that the use of the FeSi inoculant with traces of La promoted an increase in the density of counts of graphite, and that inoculation with FeB and the addition of 0.02% Mg diminished the nodularity of the graphite. Furthermore, throughout the entire thickness of the working layer, an increase in the amount of SiCaMn of up to 0.6 kg/T produced an increase in the size of the graphite particles and a marked improvement in their nodularity. Full article
(This article belongs to the Special Issue Advanced Technology for Materials Synthesis and Processing)
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Open AccessArticle Micromechanism of Cold Deformation of Two-Phase Polycrystalline Ti–Al Alloy with Void
Materials 2019, 12(1), 184; https://doi.org/10.3390/ma12010184
Received: 27 November 2018 / Revised: 25 December 2018 / Accepted: 3 January 2019 / Published: 7 January 2019
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Abstract
Cold deformation behavior of polycrystalline metallic material is affected by intrinsic defects such as dislocations, voids, inclusions etc. Existing studies on α2(Ti3Al) + γ(TiAl) two-phase Ti–Al alloy cover about deformation behavior mainly on macro [...] Read more.
Cold deformation behavior of polycrystalline metallic material is affected by intrinsic defects such as dislocations, voids, inclusions etc. Existing studies on α 2 ( Ti 3 Al ) + γ ( TiAl ) two-phase Ti–Al alloy cover about deformation behavior mainly on macro scale. This paper focuses on the cold deformation mechanism of two-phase Ti–Al alloy at micro scale, and the role of voids in deformation process. Molecular dynamics simulations were performed to study the evolution of micro structure of material under uniaxial tension. Interaction between spherical nano voids with different size and position was also examined in the simulation. The results show that (1) In elastic stage, deformation of the two-phase is coordinated, but Ti 3 Al is more deformable; (2) In plastic stage, γ phase is the major dislocation source in two-phase alloy; (3) voids detracts the strength of the two-phase alloy, while the position of void affect the degree of this subtraction, voids located at the boundary of α 2 / γ phase have significant detraction to strength. Full article
(This article belongs to the Special Issue Alloy and Process Development of Light Metals)
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Open AccessArticle Preparation and Luminescence Properties of Ba5Si8O21 Long Persistent Phosphors Doped with Rare-Earth Elements
Materials 2019, 12(1), 183; https://doi.org/10.3390/ma12010183
Received: 13 December 2018 / Revised: 28 December 2018 / Accepted: 29 December 2018 / Published: 7 January 2019
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Abstract
The phosphors of formula Ba5Si8O21:Eu2+,Dy3+ were synthesized and studied in order to improve their properties. Their synthesis conditions were evaluated as a function of precursors, crucible composition, flux agents, dopants and temperatures. The samples [...] Read more.
The phosphors of formula Ba5Si8O21:Eu2+,Dy3+ were synthesized and studied in order to improve their properties. Their synthesis conditions were evaluated as a function of precursors, crucible composition, flux agents, dopants and temperatures. The samples were characterised by means of a systematic investigation through elemental, kinetic, mineralogical (both qualitative and quantitative), and morphological analysis. This study allows for a careful evaluation of the parameters that influence the formation and properties of Ba5Si8O21:Eu2+,Dy3+ phosphors. As for the synthesis conditions, the use of Na2SiO3, BaCO3 and NH4Cl as precursors was very important to reduce the temperature and time of synthesis. The reducing atmosphere produced with purified coal was cheaper and gave results similar to the more traditional gas mixture (H2/N2). At the end of this study, a phosphor with improved long persistent phosphorescence (LPP) characteristics was obtained with Ba/Si = 0.7, Eu/Si = 2.8 × 10−3 and Dy/Si = 3.6 × 10−3 following a 6 h-synthesis in a quartz crucible. Full article
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Open AccessArticle Turning Research of Additive Laser Molten Stainless Steel 316L Obtained by 3D Printing
Materials 2019, 12(1), 182; https://doi.org/10.3390/ma12010182
Received: 17 December 2018 / Revised: 26 December 2018 / Accepted: 28 December 2018 / Published: 7 January 2019
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This paper presents the characteristic of 316L steel turning obtained by 3D printing. The analysis of the influence of turning data on the components of the total cutting force, surface roughness and the maximum temperature values in the cutting zone are presented. The [...] Read more.
This paper presents the characteristic of 316L steel turning obtained by 3D printing. The analysis of the influence of turning data on the components of the total cutting force, surface roughness and the maximum temperature values in the cutting zone are presented. The form of chips obtained in the machining process was also analyzed. Statistical analysis of the test results was developed using the Taguchi method. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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Open AccessFeature PaperArticle Improvement of a Cohesive Zone Model for Fatigue Delamination Rate Simulation
Materials 2019, 12(1), 181; https://doi.org/10.3390/ma12010181
Received: 29 November 2018 / Revised: 24 December 2018 / Accepted: 29 December 2018 / Published: 7 January 2019
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The cohesive zone model (CZM) has found wide acceptance as a tool for the simulation of delamination in composites and debonding in bonded joints and various implementations of the cohesive zone model dedicated to fatigue problems have been proposed in the past decade. [...] Read more.
The cohesive zone model (CZM) has found wide acceptance as a tool for the simulation of delamination in composites and debonding in bonded joints and various implementations of the cohesive zone model dedicated to fatigue problems have been proposed in the past decade. In previous works, the authors have developed a model based on cohesive zone to simulate the propagation of fatigue defects where damage acts on cohesive stiffness, with an initial (undamaged) stiffness representative of that of the entire thickness of an adhesive layer. In the case of a stiffness that is order of magnitude higher than the previous one (for instance, in the simulation of the ply-to-ply interface in composites), the model prediction becomes inaccurate. In this work, a new formulation of the model that overcomes this limitation is developed. Finite element simulations have been conducted on a mode I, constant bending (constant G)-loaded double cantilever beam (DCB) joint to assess the response of the new model with respect to the original one for varying initial stiffness K0 and cohesive strength σ0. The results showed that the modified model is robust with respect to changes of two orders of magnitude in initial stiffness and of a factor of two in σ0. Full article
(This article belongs to the Special Issue Carbon Fibre Reinforced Plastics)
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Open AccessArticle Influence of Alloy Substrate Treatment on Microstructure and Surface Performances of Arc-Ion Plated Gold-Like Film
Materials 2019, 12(1), 180; https://doi.org/10.3390/ma12010180
Received: 17 November 2018 / Revised: 26 December 2018 / Accepted: 28 December 2018 / Published: 7 January 2019
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Three typical surface pretreatment strategies (grind, drawing, polishing) are employed to explore the influence of alloy substrate treatment on microstructure and surface performances of arc-ion plated TiN and ZrN films. The luminance and color of the films are measured by the color coordinate [...] Read more.
Three typical surface pretreatment strategies (grind, drawing, polishing) are employed to explore the influence of alloy substrate treatment on microstructure and surface performances of arc-ion plated TiN and ZrN films. The luminance and color of the films are measured by the color coordinate value of CIELab system (a color system which is defined by the International Commission on illumination). The crystal phases, morphology and microstructure are characterized and analyzed by scanning electron microscope (SEM) and X-ray powder diffraction (XRD). In addition, the anti-alkali, salt corrosion and anti-oxidation performances of films are systematically researched. The results show that the films with grinding pretreatment are more like gold color, “L” values are 77.27 cd/m2 and 80.30 cd/m2. The “b” value of TiN film is 29.96, which is the same as that of pure gold. The “a” value of ZrN film is 0.31, which is the same as pure silver. The density of TiN and ZrN films is the best, and both TiN and ZrN films were crystalline. They have the best anti-alkali and anti-oxidation performance. The films with drawing pretreatment show slant red color and have medium brightness values (74.07–76.37 cd/m2), worse compactness, obvious furrows and holes in their microstructures and worse salt corrosion and anti-oxidation performances. However, the TiN films are in amorphous states. The films with polishing pretreatment have the lowest brightness (72.66 cd/m2), gold-like color, superior compactness and best salt corrosion performance, which have a small number of holes. The TiN films with polishing pretreatment are also in amorphous state. Above all, alloy substrate pretreatment by grinding has the best gold-like color, brightness, compactness and corrosion resistance performance. This work exclusively sheds new light on surface pretreatment of alloy substrate by arc-ion plated films and also provides a reference for corrosion resistance performance of gold-like films. Full article
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Open AccessArticle Increasing Uptake of Silica Nanoparticles with Electroporation: From Cellular Characterization to Potential Applications
Materials 2019, 12(1), 179; https://doi.org/10.3390/ma12010179
Received: 10 December 2018 / Revised: 21 December 2018 / Accepted: 29 December 2018 / Published: 7 January 2019
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Abstract
In the fields of biology and medicine, nanoproducts such as nanoparticles (NPs) are specifically interesting as theranostic tools, since they offer the double capacity to locally deliver active drugs and to image exactly where the product is delivered. Among the many described possibilities, [...] Read more.
In the fields of biology and medicine, nanoproducts such as nanoparticles (NPs) are specifically interesting as theranostic tools, since they offer the double capacity to locally deliver active drugs and to image exactly where the product is delivered. Among the many described possibilities, silica nanoparticles (SiNPs) represent a good choice because of their ease of synthesis, the possibility of their vast functionalization, and their good biocompatibility. However, SiNPs’ passive cell internalization by endocytosis only distributes NPs into the cell cytoplasm and is unable to target the nucleus if SiNPs are larger than a few nanometers. In this study, we demonstrate that the cell penetration of SiNPs of 28–30 nm in diameter can be strongly enhanced using a physical method, called electroporation or electropermeabilization (EP). The uptake of fluorescently labelled silica nanoparticles was improved in two different cancer cell lines, namely, HCT-116 (human colon cancer) cells and RL (B-lymphoma) cells. First, we studied cells’ capability for the regular passive uptake of SiNPs in vitro. Then, we set EP parameters in order to induce a more efficient and rapid cell loading, also comprising the nuclear compartment, while preserving the cell viability. In the final approach, we performed in vivo experiments, and evidenced that the labeling was long-lasting, as confirmed by fluorescence imaging of labeled tumors, which enabled a 30-day follow-up. This kind of SiNPs delivery, achieved by EP, could be employed to load extensive amounts of active ingredients into the cell nucleus, and concomitantly allow the monitoring of the long-term fate of nanoparticles. Full article
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Open AccessArticle Self-Propagating Synthesis and Characterization Studies of Gd-Bearing Hf-Zirconolite Ceramic Waste Forms
Materials 2019, 12(1), 178; https://doi.org/10.3390/ma12010178
Received: 14 December 2018 / Revised: 28 December 2018 / Accepted: 30 December 2018 / Published: 7 January 2019
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Abstract
Synroc is recognized as the second-generation waste matrice for nuclear waste disposal. Zirconolite is one of the most durable Synroc minerals. In this study, Gd and Hf were selected as the surrogates of trivalent and tetravalent actinide nuclides. Gd-bearing Hf-zirconolite (Ca1−xHf [...] Read more.
Synroc is recognized as the second-generation waste matrice for nuclear waste disposal. Zirconolite is one of the most durable Synroc minerals. In this study, Gd and Hf were selected as the surrogates of trivalent and tetravalent actinide nuclides. Gd-bearing Hf-zirconolite (Ca1−xHf1−xGd2xTi2O7) ceramic waste forms were rapidly synthesized from a self-propagating technique using CuO as the oxidant. The results indicate that Gd can concurrently replace the Ca and Hf sites. However, Gd2O3 could not completely be incorporated into the lattice structure of zirconolite when the x value is higher than 0.8. The aqueous durability of selected Gd-Hf codoped sample (Hf-Gd-0.6) was tested, where the 42 days normalized leaching rates (LRi) of Ca, Cu, Gd and Hf are measured to be 1.57, 0.13, 4.72 × 10−7 and 1.59 × 10−8 g·m−2·d−1. Full article
(This article belongs to the Special Issue Multifunctional Oxide-Based Materials: From Synthesis to Application)
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Open AccessArticle Influence of Different Grades of CBN Inserts on Cutting Force and Surface Roughness of AISI H13 Die Tool Steel during Hard Turning Operation
Materials 2019, 12(1), 177; https://doi.org/10.3390/ma12010177
Received: 19 November 2018 / Revised: 24 December 2018 / Accepted: 28 December 2018 / Published: 7 January 2019
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Abstract
Now-a-days, the application of hard tuning with CBN tool has been massively increased because the hard turning is a good alternative to grinding process. However, there are some issues that need to be addressed related to the CBN grades and their particular applications [...] Read more.
Now-a-days, the application of hard tuning with CBN tool has been massively increased because the hard turning is a good alternative to grinding process. However, there are some issues that need to be addressed related to the CBN grades and their particular applications in the area of hard turning process. This experimental study investigated the effects of three different grades of CBN insert on the cutting forces and surface roughness. The process of hard turning was made using the AISI H13 die tool steel at containing different hardness (45 HRC, 50 HRC and 55 HRC) levels. The work material were selected on the basis of its application in the die making industries in a range of hardness of 45–55 HRC. Optimization by the central composite design approach has been used for design and analysis. The present study reported that the cutting forces and surface roughness are influenced by the alloying elements and percentage of CBN in the cutting tool material. The work material hardness, feed rate and cutting speed are found to be statistically significant on the responses. Furthermore, a comparative performance between the three different grades of CBN inserts has been shown on the cutting forces and surface roughness at different workpiece hardness. To obtain the optimum parameters from multiple responses, desirability approach has been used. The novelty/robustness of the present study is represented by its great contribution to solve practical industrial application when is developed a new process using different CBN grades for hard turning and die makers of workpiece having the hardness between 45 and 55 HRC. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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Open AccessArticle Mechanical Properties and Microstructure of DMLS Ti6Al4V Alloy Dedicated to Biomedical Applications
Materials 2019, 12(1), 176; https://doi.org/10.3390/ma12010176
Received: 17 December 2018 / Revised: 28 December 2018 / Accepted: 2 January 2019 / Published: 7 January 2019
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Abstract
The aim of this work was to investigate the microstructure and mechanical properties of samples produced by direct metal laser sintering (DMLS) with varied laser beam speed before and after heat treatment. Optical analysis of as-built samples revealed microstructure built of martensite needles [...] Read more.
The aim of this work was to investigate the microstructure and mechanical properties of samples produced by direct metal laser sintering (DMLS) with varied laser beam speed before and after heat treatment. Optical analysis of as-built samples revealed microstructure built of martensite needles and columnar grains, growing epitaxially towards the built direction. External and internal pores, un-melted or semi-melted powder particles and inclusions in the examined samples were also observed. The strength and Young’s modulus of the DMLS samples before heat treatment was higher than for cast and forged samples; however, the elongation at break for vertical and horizontal orientation was lower than required for biomedical implants. After heat treatment, the hardness of the samples decreased, which is associated with the disappearance of boundary effect and martensite decomposition to lamellar mixture of α and β, and the anisotropic behaviour of the material also disappears. Ultimate tensile strength (UTS) and yield strength(YS) also decreased, while elongation increased. Tensile properties were sensitive to the build orientation, which indicates that DMLS generates anisotropy of material as a result of layered production and elongated β prior grains. It was noticed that inappropriate selection of parameters did not allow properties corresponding to the standards to be obtained due to the high porosity and defects of the microstructure caused by insufficient energy density. Full article
(This article belongs to the Section Biomaterials)
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Open AccessArticle Design of an Integrated Optics Sensor Structure Based on Diamond Waveguide for Hemoglobin Property Detection
Materials 2019, 12(1), 175; https://doi.org/10.3390/ma12010175
Received: 30 November 2018 / Revised: 23 December 2018 / Accepted: 2 January 2019 / Published: 7 January 2019
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Abstract
This manuscript presents a theoretical analysis of a diamond-based integrated optics structure for applications in biosensors. The geometrical, optical, and sensitivity properties of an integrated optical structure were theoretically analyzed and optimized for biosensor applications. The analysis focused on determining the waveguide properties, [...] Read more.
This manuscript presents a theoretical analysis of a diamond-based integrated optics structure for applications in biosensors. The geometrical, optical, and sensitivity properties of an integrated optical structure were theoretically analyzed and optimized for biosensor applications. The analysis focused on determining the waveguide properties, including the effective refractive index Neff as a function of refractive index nw and thickness dw of waveguide layer, refractive index of the hemoglobin cover layer ncH and substrate layer ns, homogeneous sensitivity dNeff/dncH, and modal field distribution of guided waveguide modes. The analysis was completed for two types of waveguide layer materials: undoped or boron-doped diamond films with or without the hemoglobin cover layer. The presented experimental results form a base for developing biosensor structures based on integrated optics for determining the properties of hemoglobin. Full article
(This article belongs to the Special Issue Design and Synthesis of Novel Optical Probes)
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Open AccessArticle Microstructure and Flexural Properties of Z-Pinned Carbon Fiber-Reinforced Aluminum Matrix Composites
Materials 2019, 12(1), 174; https://doi.org/10.3390/ma12010174
Received: 5 December 2018 / Revised: 28 December 2018 / Accepted: 28 December 2018 / Published: 7 January 2019
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Abstract
Z-pinning can significantly improve the interlaminar shear properties of carbon fiber-reinforced aluminum matrix composites (Cf/Al). However, the effect of the metal z-pin on the in-plane properties of Cf/Al is unclear. This study examines the effect of the z-pin on the flexural strength and [...] Read more.
Z-pinning can significantly improve the interlaminar shear properties of carbon fiber-reinforced aluminum matrix composites (Cf/Al). However, the effect of the metal z-pin on the in-plane properties of Cf/Al is unclear. This study examines the effect of the z-pin on the flexural strength and failure mechanism of Cf/Al composites with different volume contents and diameters of the z-pins. The introduction of a z-pin leads to the formation of a brittle phase at the z-pin/matrix interface and microstructural damage such as aluminum-rich pockets and carbon fiber waviness, thereby resulting in a reduction of the flexural strength. The three-point flexural test results show that the adding of a metal z-pin results in reducing the Cf/Al composites’ flexural strength by 2–25%. SEM imaging of the fracture surfaces revealed that a higher degree of interfacial reaction led to more cracks on the surface of the z-pin. This crack-susceptible interface layer between the z-pin and the matrix is likely the primary cause of the reduction of the flexural strength. Full article
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Open AccessArticle Effects on the Mechanical Properties of Nacre-Like Bio-Hybrid Membranes with Inter-Penetrating Petal Structure Based on Magadiite
Materials 2019, 12(1), 173; https://doi.org/10.3390/ma12010173
Received: 29 November 2018 / Revised: 24 December 2018 / Accepted: 2 January 2019 / Published: 7 January 2019
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Abstract
Rigid biological systems are increasingly becoming a source of inspiration for the fabrication of the advanced functional materials due to their diverse hierarchical structures and remarkable engineering properties. As a bionic biomaterial with a clear layered structure, excellent mechanical properties, and interesting rainbow [...] Read more.
Rigid biological systems are increasingly becoming a source of inspiration for the fabrication of the advanced functional materials due to their diverse hierarchical structures and remarkable engineering properties. As a bionic biomaterial with a clear layered structure, excellent mechanical properties, and interesting rainbow colors, nacre has become one of the most attractive models for novel artificial materials design. In this research paper, the tough and strong nacre-like bio-hybrid membranes with an interpenetrating petals structure were fabricated from chitosan (CS) and magadiite (MAG) clay nanosheets through the gel-casting self-assembling method. The analyses from X-ray diffraction (XRD), scanning electron microscope (SEM), and observations of water droplets on membranes indicated that the nacre-like hybrid membranes had a layered compact structure. Fourier transforms infrared spectroscopy (FTIR) analyses suggested that the CS molecular chains formed chemical bonds and hydrogen bonds with MAG layers. The inter-penetrating petal layered structure had a good effect on the mechanical properties of a nacre-like bio-hybrid membranes and the tensile strength of the hybrid membranes could reach at 78.6 MPa. However, the transmission analyses of the results showed that the hybrid membranes still had a certain visible light transmittance. Finally, the hybrid membranes possessed an intriguing efficient fire-shielding property during exposure to the flame of alcohol burner. Consequently, the great biocompatibility and excellent mechanical properties of the bio-hybrid membranes with the special interpenetrating petals structure provides a great opportunity for these composites to be widely applied in biomaterial research. Full article
(This article belongs to the Special Issue Polymeric Nanocomposites for Flexible Sensor)
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Open AccessArticle Study of the Microstructure and Crack Evolution Behavior of Al-5Fe-1.5Er Alloy
Materials 2019, 12(1), 172; https://doi.org/10.3390/ma12010172
Received: 19 November 2018 / Revised: 24 December 2018 / Accepted: 29 December 2018 / Published: 7 January 2019
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Abstract
In this work, the microstructure of Al-5Fe-1.5Er alloy was characterized and analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) techniques. The effect of microstructure on the behavior of crack initiation and propagation was [...] Read more.
In this work, the microstructure of Al-5Fe-1.5Er alloy was characterized and analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) techniques. The effect of microstructure on the behavior of crack initiation and propagation was investigated using in situ tensile testing. The results showed that when 1.5 wt.% Er was added in the Al-5Fe alloy, the microstructure consisted of α-Al matrix, Al3Fe, Al4Er, and Al3Fe + Al4Er eutectic phases. The twin structure of Al3Fe phase was observed, and the twin plane was {001}. Moreover, a continuous concave and convex interface structure of Al4Er was observed. Furthermore, Al3Fe was in the form of a sheet with a clear gap inside. In situ tensile tests of the alloy at room temperature showed that the crack initiation mainly occurred in the Al3Fe phase, and that the crack propagation modes included intergranular and trans-granular expansions. The crack trans-granular expansion was due to the strong binding between Al4Er phases and surrounding organization, whereas the continuous concave and convex interface structure of Al4Er provided a significant meshing effect on the matrix and the eutectic structure. Full article
(This article belongs to the Special Issue Advanced Materials for Transport Applications)
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Open AccessArticle The Development of a Surface Finisher of Car Park Slab Using Waterborne Silicon Acrylic with Polyamide [Part I: Performance Evaluation]
Materials 2019, 12(1), 171; https://doi.org/10.3390/ma12010171
Received: 30 November 2018 / Revised: 29 December 2018 / Accepted: 31 December 2018 / Published: 7 January 2019
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Abstract
A waterborne coating system for car park slab has recently gained interest as an alternative for solvent-based finishing materials due to environmental concerns and prolongation of service life. However, water-based finishers, regardless of their eco-friendly properties, have relatively lower hardness compared to traditional [...] Read more.
A waterborne coating system for car park slab has recently gained interest as an alternative for solvent-based finishing materials due to environmental concerns and prolongation of service life. However, water-based finishers, regardless of their eco-friendly properties, have relatively lower hardness compared to traditional finishing systems. In order to overcome this obstacle, a hybrid technology was used to develop a substitute surface finisher for car park slab and its performance was evaluated according to the KS (Korean Standard) F 4937. Initially, the proper mix ratio of polyamide was found by comparing adhesion via pull-off-test results and other performance evaluation tests. From the test results, it was found that mixing polyamide with silicon acrylic finisher caused an increase in adhesion strength. Silicon acrylic with a 30% mix ratio of polyamide resin (SA+PR30%) was selected to perform the rest of the tests and the results satisfied the acceptance criteria of KS F 4937 and were compared with a recent water-based polyurethane finisher with cementitious powder (WPC). Finally, it was verified that the developed finisher could be an alternative finisher of urethane and epoxy finishers as it has good mechanical properties and emit less volatile organic compounds (VOC). Full article
(This article belongs to the Special Issue Selected Papers from IMETI2018)
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Open AccessFeature PaperArticle Solid-Gas Phase Photo-Catalytic Behaviour of Rutile and TiOn (1 < n < 2) Sub-Oxide Phases for Self-Cleaning Applications
Materials 2019, 12(1), 170; https://doi.org/10.3390/ma12010170
Received: 18 November 2018 / Revised: 20 December 2018 / Accepted: 29 December 2018 / Published: 7 January 2019
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Abstract
The solid-gas phase photo-catalytic activities of rutile TiO2 and TiOn (1 < n < 2) sub-oxide phases have been evaluated. Varying concentrations of Ti3+ defects were introduced into the rutile polymorph of titanium dioxide through carbo-thermal reduction at temperatures ranging [...] Read more.
The solid-gas phase photo-catalytic activities of rutile TiO2 and TiOn (1 < n < 2) sub-oxide phases have been evaluated. Varying concentrations of Ti3+ defects were introduced into the rutile polymorph of titanium dioxide through carbo-thermal reduction at temperatures ranging from 350 °C to 1300 °C. The resulting sub-oxides formed were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, impedance spectroscopy and UV-visible diffuse reflectance spectroscopy. The presence of Ti3+ in rutile exposed to high reduction temperatures was confirmed by X-ray diffraction. In addition, a Ti3+-Ti4+ system was demonstrated to enhance the photo-catalytic properties of rutile for the degradation of the air pollutants NO2 and CO2 under UV irradiation of wavelengths (λ) 376–387 nm and 381–392 nm. The optimum reduction temperature for photo-catalytic activity was within the range 350–400 °C and attributed to improved charge-separation. The materials that were subject to carbo-thermal reduction at temperatures of 350 °C and 400 °C exhibited electrical conductivities over one hundred times higher compared to the non-reduced rutile. The results highlight that sub-oxide phases form an important alternative approach to doping with other elements to improve the photo-catalytic performance of TiO2. Such materials are important for applications such as self-cleaning where particles can be incorporated into surface coatings. Full article
(This article belongs to the Special Issue Self-Cleaning Surfaces)
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Open AccessArticle Comparing the Through-Thickness Gradient of the Deformed and Recrystallized Microstructure in Tantalum with Unidirectional and Clock Rolling
Materials 2019, 12(1), 169; https://doi.org/10.3390/ma12010169
Received: 9 December 2018 / Revised: 25 December 2018 / Accepted: 28 December 2018 / Published: 7 January 2019
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Abstract
Controlling the microstructure homogeneity is crucial in achieving high quality tantalum (Ta) sputtering targets used in integrated circuit fabrication. Unluckily, traditional rolling easily generates a microstructure gradient along the thickness direction in Ta sheets. The deformation and recrystallization behavior of unidirectional and clock [...] Read more.
Controlling the microstructure homogeneity is crucial in achieving high quality tantalum (Ta) sputtering targets used in integrated circuit fabrication. Unluckily, traditional rolling easily generates a microstructure gradient along the thickness direction in Ta sheets. The deformation and recrystallization behavior of unidirectional and clock rolled Ta with an 87% strain were therefore systematically compared to investigate whether the change of strain-pass can effectively ameliorate the microstructure gradient along the thickness. Electron backscatter diffraction was used to analyze the misorientation characteristics of the deformed grains. A strong microstructure gradient exists in the unidirectional rolled (UR) sheets. Many microshear bands and well-defined microbands occurred in {111} deformed grains in the UR sheets, especially in the center region, while the grain fragmentation with {111} and {100} orientation in the clock rolled (CR) sheets was more homogenous along the thickness. The kernel average misorientation (KAM) and grain reference orientation deviation-hyper (GROD-Hyper) further confirmed these differences. X-ray line profile analysis (XLPA) indicated that the stored energy distribution was more inhomogeneous in the UR sheets. Schmid factor analysis suggested that the strain path changes due to clock rolling promoted the activation of multiple slip systems in {111} oriented grains. Upon static annealing, homogeneous nucleation combined with a slower grain growth rate resulted in finer and more uniform grain size for the CR sheet. In contrast, a strong recrystallization microstructure-gradient along the thickness formed in the UR sheets, which is attributed to the fact that the higher stored energy and more preferential nucleation sites led to faster recrystallization in the center region, as compared with the surface region. Thus, clock rolling can effectively improve the homogeneity of the through-thickness recrystallization microstructure of Ta sheets. Full article
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Open AccessArticle Investigation of the Potential Use of Calcium Alginate Capsules for Self-Healing in Porous Asphalt Concrete
Materials 2019, 12(1), 168; https://doi.org/10.3390/ma12010168
Received: 21 November 2018 / Revised: 6 December 2018 / Accepted: 29 December 2018 / Published: 7 January 2019
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Abstract
Improving the healing capacity of asphalt is proving to be an effective method to prolong the service life of an asphalt pavement. The calcium alginate capsules encapsulating rejuvenator have been developed and proved to provide successful localized crack healing in asphalt mastic. However, [...] Read more.
Improving the healing capacity of asphalt is proving to be an effective method to prolong the service life of an asphalt pavement. The calcium alginate capsules encapsulating rejuvenator have been developed and proved to provide successful localized crack healing in asphalt mastic. However, it is not known whether this self-healing asphalt system will improve healing capacity of a full asphalt mix. To this aim, this paper reports on study which investigate effect of the calcium alginate capsules onto self-healing capacity of the porous asphalt mix. X-ray computed tomography (XCT) was used to visualize the distribution of the capsules in porous asphalt. The effect of the capsules on fracture resistance of porous asphalt concrete was studied by semi-circular bending (SCB) tests. A semi-circular bending and healing programme was carried out to evaluate the healing effect of these capsules in porous asphalt concrete. Indirect Tensile Stiffness Modulus (ITSM) tests were employed in order to investigate the influence of the capsules on the stiffness of the porous asphalt concrete. The results indicate that incorporating calcium alginate capsules significantly improve the healing capacity of porous asphalt concrete without compromising its performance. Full article
(This article belongs to the Special Issue Environment-Friendly Construction Materials)
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Open AccessArticle The Effect of the Isomeric Chlorine Substitutions on the Honeycomb-Patterned Films of Poly(x-chlorostyrene)s/Polystyrene Blends and Copolymers via Static Breath Figure Technique
Materials 2019, 12(1), 167; https://doi.org/10.3390/ma12010167
Received: 30 November 2018 / Revised: 20 December 2018 / Accepted: 31 December 2018 / Published: 7 January 2019
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Abstract
Polymeric thin films patterned with honeycomb structures were prepared from poly(x-chlorostyrene) and statistical poly(x-chlorostyrene-co-styrene) copolymers by static breath figure method. Each polymeric sample was synthesized by free radical polymerization and its solution in tetrahydrofuran cast on glass wafers under 90% relative humidity (RH). [...] Read more.
Polymeric thin films patterned with honeycomb structures were prepared from poly(x-chlorostyrene) and statistical poly(x-chlorostyrene-co-styrene) copolymers by static breath figure method. Each polymeric sample was synthesized by free radical polymerization and its solution in tetrahydrofuran cast on glass wafers under 90% relative humidity (RH). The effect of the chorine substitution in the topography and conformational entropy was evaluated. The entropy of each sample was calculated by using Voronoi tessellation. The obtained results revealed that these materials could be a suitable toolbox to develop a honeycomb patterns with a wide range of pore sizes for a potential use in contact guidance induced culture. Full article
(This article belongs to the Special Issue Polymeric Materials: Surfaces, Interfaces and Bioapplications)
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