Materials

8 pages, 2167 KiB

Open AccessEditor’s ChoiceArticle

Formation of Li₂CO₃ Nanostructures for Lithium-Ion Battery Anode Application by Nanotransfer Printing

by Tae Wan Park, Young Lim Kang, Sang Hyeon Lee, Gu Won No, Eun-Soo Park, Chan Park, Junghoon Lee and Woon Ik Park

Materials 2021, 14(7), 1585; https://doi.org/10.3390/ma14071585 - 24 Mar 2021

Viewed by 3271

Abstract

Various high-performance anode and cathode materials, such as lithium carbonate, lithium titanate, cobalt oxides, silicon, graphite, germanium, and tin, have been widely investigated in an effort to enhance the energy density storage properties of lithium-ion batteries (LIBs). However, the structural manipulation of anode [...] Read more.

Various high-performance anode and cathode materials, such as lithium carbonate, lithium titanate, cobalt oxides, silicon, graphite, germanium, and tin, have been widely investigated in an effort to enhance the energy density storage properties of lithium-ion batteries (LIBs). However, the structural manipulation of anode materials to improve the battery performance remains a challenging issue. In LIBs, optimization of the anode material is a key technology affecting not only the power density but also the lifetime of the device. Here, we introduce a novel method by which to obtain nanostructures for LIB anode application on various surfaces via nanotransfer printing (nTP) process. We used a spark plasma sintering (SPS) process to fabricate a sputter target made of Li₂CO₃, which is used as an anode material for LIBs. Using the nTP process, various Li₂CO₃ nanoscale patterns, such as line, wave, and dot patterns on a SiO₂/Si substrate, were successfully obtained. Furthermore, we show highly ordered Li₂CO₃ nanostructures on a variety of substrates, such as Al, Al₂O₃, flexible PET, and 2-Hydroxylethyl Methacrylate (HEMA) contact lens substrates. It is expected that the approach demonstrated here can provide new pathway to generate many other designable structures of various LIB anode materials. Full article

(This article belongs to the Special Issue Spontaneous Self-Assembly of Spatially Ordered Structures)

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13 pages, 4921 KiB

Open AccessEditor’s ChoiceArticle

High-Performance Complementary Electrochromic Device Based on Iridium Oxide as a Counter Electrode

by Tien-Fu Ko, Po-Wen Chen, Kuan-Ming Li, Hong-Tsu Young, Chen-Te Chang and Sheng-Chuan Hsu

Materials 2021, 14(7), 1591; https://doi.org/10.3390/ma14071591 - 24 Mar 2021

Cited by 15 | Viewed by 2784

Abstract

In complementary electrochromic devices (ECDs), nickel oxide (NiO) is generally used as a counter electrode material for enhancing the coloration efficiency. However, an NiO film as a counter electrode in ECDs is susceptible to degradation upon prolonged electrochemical cycling, which leads to an [...] Read more.

In complementary electrochromic devices (ECDs), nickel oxide (NiO) is generally used as a counter electrode material for enhancing the coloration efficiency. However, an NiO film as a counter electrode in ECDs is susceptible to degradation upon prolonged electrochemical cycling, which leads to an insufficient device lifetime. In this study, a type of counter electrode iridium oxide (IrO₂) layer was fabricated using vacuum cathodic arc plasma (CAP). We focused on the comparison of IrO₂ and NiO deposited on a 5 × 5 cm² indium tin oxide (ITO) glass substrate with various Ar/O₂ gas-flow ratios (1/2, 1/2.5, and 1/3) in series. The optical performance of IrO₂-ECD (glass/ITO/WO₃/liquid electrolyte/IrO₂/ITO/glass) was determined by optical transmittance modulation; ∆T = 50% (from T_bleaching (75%) to T_coloring (25%)) at 633 nm was higher than that of NiO-ECD (ITO/NiO/liquid electrolyte/WO₃/ITO) (∆T = 32%). Apart from this, the ECD device demonstrated a fast coloring time of 4.8 s, a bleaching time of 1.5 s, and good cycling durability, which remained at 50% transmittance modulation even after 1000 cycles. The fast time was associated with the IrO₂ electrode and provided higher diffusion coefficients and a filamentary shape as an interface that facilitated the transfer of the Li ions into/out of the interface electrodes and the electrolyte. In our result of IrO₂-ECD analyses, the higher optical transmittance modulation was useful for promoting electrochromic application to a cycle durability test as an alternative to NiO-ECD. Full article

(This article belongs to the Section Thin Films and Interfaces)

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14 pages, 8759 KiB

Open AccessEditor’s ChoiceArticle

A New Methodology for Predicting Brittle Fracture of Plastically Deformable Materials: Application to a Cold Shell Nosing Process

by Jae Gun Eom, Sang Woon Byun, Seung Won Jeong, Wan Jin Chung and Man Soo Joun

Materials 2021, 14(7), 1593; https://doi.org/10.3390/ma14071593 - 24 Mar 2021

Cited by 4 | Viewed by 2238

Abstract

The traditional theory of ductile fracture has limitations for predicting crack generation during a cold shell nosing process. Various damage criteria are employed to explain fracture and failure in the nose part of a cold shell. In this study, differences in microstructure among [...] Read more.

The traditional theory of ductile fracture has limitations for predicting crack generation during a cold shell nosing process. Various damage criteria are employed to explain fracture and failure in the nose part of a cold shell. In this study, differences in microstructure among fractured materials and analysis of their surfaces indicated the occurrence of brittle fractures. The degree of “plastic deformation-induced embrittlement” (PDIE) of plastically deformable materials affects the likelihood of brittle fractures; PDIE can also decrease the strength in tension due to the Bauschinger effect. Two indicators of brittle fracture are presented, i.e., the critical value of PDIE and the allowable tensile strength (which in turn depends on the degree of PDIE or embrittlement-effective strain). When the maximum principal stress is greater than the latter and the PDIE is greater than the former, our method determines the likelihood of brittle fracture. This approach was applied to an actual cold shell nosing process, and the predictions were in good quantitative agreement with the experimental results. Full article

(This article belongs to the Special Issue Metal Forming: Processes and Analyses)

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3 pages, 189 KiB

Open AccessEditor’s ChoiceEditorial

Environment-Friendly Electrochemical Processes

by Carlos A. Martínez-Huitle

Materials 2021, 14(6), 1548; https://doi.org/10.3390/ma14061548 - 22 Mar 2021

Cited by 8 | Viewed by 2344

Abstract

The present water crisis is probable to grow worse in the coming decades, and this has motivated the scientific community to identify innovative, safe, and robust water treatment technologies at a lower cost and with less energy, diminishing the use of chemicals and [...] Read more.

The present water crisis is probable to grow worse in the coming decades, and this has motivated the scientific community to identify innovative, safe, and robust water treatment technologies at a lower cost and with less energy, diminishing the use of chemicals and impact on the environment [...] Full article

(This article belongs to the Special Issue Environment-Friendly Electrochemical Processes)

14 pages, 3111 KiB

Open AccessEditor’s ChoiceArticle

Scattering Mechanisms and Suppression of Bipolar Diffusion Effect in Bi₂Te_2.85Se_0.15I_x Compounds

by Jin Hee Kim, Song Yi Back, Jae Hyun Yun, Ho Seong Lee and Jong-Soo Rhyee

Materials 2021, 14(6), 1564; https://doi.org/10.3390/ma14061564 - 22 Mar 2021

Cited by 13 | Viewed by 2907

Abstract

We investigated the anisotropic thermoelectric properties of the Bi₂Te_2.85Se_0.15I_x (x = 0.0, 0.1, 0.3, 0.5 mol.%) compounds, synthesized by ball-milling and hot-press sintering. The electrical conductivities of the Bi₂Te_2.85Se_0.15I_x [...] Read more.

We investigated the anisotropic thermoelectric properties of the Bi₂Te_2.85Se_0.15I_x (x = 0.0, 0.1, 0.3, 0.5 mol.%) compounds, synthesized by ball-milling and hot-press sintering. The electrical conductivities of the Bi₂Te_2.85Se_0.15I_x were significantly improved by the increase of carrier concentration. The dominant electronic scattering mechanism was changed from the mixed (T ≤ 400 K) and ionization scattering (T ≥ 420 K) for pristine compound (x = 0.0) to the acoustic phonon scattering by the iodine doping. The Hall mobility was also enhanced with the increasing carrier concentration. The enhancement of Hall mobility was caused by the increase of the mean free path of the carrier from 10.8 to 17.7 nm by iodine doping, which was attributed to the reduction of point defects without the meaningful change of bandgap energy. From the electron diffraction patterns, a lattice distortion was observed in the iodine doped compounds. The modulation vector due to lattice distortion increased with increasing iodine concentration, indicating the shorter range lattice distortion in real space for the higher iodine concentration. The bipolar thermal conductivity was suppressed, and the effective masses were increased by iodine doping. It suggests that the iodine doping minimizes the ionization scattering giving rise to the suppression of the bipolar diffusion effect, due to the prohibition of the Bi_Te1 antisite defect, and induces the lattice distortion which decreases lattice thermal conductivity, resulting in the enhancement of thermoelectric performance. Full article

(This article belongs to the Special Issue Novel Thermoelectric Materials and Device Design Concepts)

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14 pages, 2767 KiB

Open AccessEditor’s ChoiceArticle

Microstructural and Corrosion Properties of Hydroxyapatite Containing PEO Coating Produced on AZ31 Mg Alloy

by Luca Pezzato, Katya Brunelli, Stefano Diodati, Mirko Pigato, Massimiliano Bonesso and Manuele Dabalà

Materials 2021, 14(6), 1531; https://doi.org/10.3390/ma14061531 - 21 Mar 2021

Cited by 45 | Viewed by 3530

Abstract

In this work, the composition of an electrolyte was selected and optimized to induce the formation of hydroxyapatite during Plasma electrolytic oxidation (PEO) treatment on an AZ31 alloy for application in bioabsorbable implants. In detail, the PEO process, called PEO-BIO (Plasma Electrolytic Oxidation-Biocompatible), [...] Read more.

In this work, the composition of an electrolyte was selected and optimized to induce the formation of hydroxyapatite during Plasma electrolytic oxidation (PEO) treatment on an AZ31 alloy for application in bioabsorbable implants. In detail, the PEO process, called PEO-BIO (Plasma Electrolytic Oxidation-Biocompatible), was performed using a silicate-phosphate-based electrolyte with the addition of calcium oxide in direct-current mode using high current densities and short treatment times. For comparison, a known PEO process for producing anticorrosive coatings, called standard, was applied on the same alloy. The coatings were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and XPS analyses. The corrosion performance was evaluated in simulated body fluid (SBF) at 37 °C. The coating produced on the PEO-BIO sample was porous and thicker than the standard PEO one, with zones enriched in Ca and P. The XRD analysis showed the formation of hydroxyapatite and calcium oxides in addition to magnesium-silicon oxide and magnesium oxide in the PEO-BIO sample. The corrosion resistance of PEO-BIO sample was comparable with that of a traditional PEO treated sample, and higher than that of the untreated alloy. Full article

(This article belongs to the Special Issue Magnesium and Its Alloys as Biodegradable Implants)

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12 pages, 1563 KiB

Open AccessEditor’s ChoiceArticle

Nanostructured Oxide-Based Systems for the pH-Triggered Release of Cinnamaldehyde

by Carolina Cionti, Tommaso Taroni, Valentina Sabatini and Daniela Meroni

Materials 2021, 14(6), 1536; https://doi.org/10.3390/ma14061536 - 21 Mar 2021

Cited by 10 | Viewed by 3148

Abstract

Cinnamaldehyde is a natural product with antibacterial, antifungal, and anti-inflammatory properties, poorly stable in environmental conditions. Systems for the controlled release of cinnamaldehyde are of great interest to the food and pharmaceutical industries. Here, a new oxide-based construct for the release of cinnamaldehyde [...] Read more.

Cinnamaldehyde is a natural product with antibacterial, antifungal, and anti-inflammatory properties, poorly stable in environmental conditions. Systems for the controlled release of cinnamaldehyde are of great interest to the food and pharmaceutical industries. Here, a new oxide-based construct for the release of cinnamaldehyde catalyzed by acidic pH was obtained by a facile grafting method based on amino-silane linkers and imine chemistry. The grafting procedure led to a loading of ca. 5 molecules/nm², determined on oxide powders with CHN and TGA measurements. The covalent grafting of cinnamaldehyde, demonstrated by FTIR analyses, preserved the molecule stability, simplifying storage. Release tests were performed at different pH values (between 5.0 and 7.4). Thanks to imine chemistry, a fast cinnamaldehyde (CIN) release was observed in a pH 5.0 environment. Using 1 mg/mL suspensions, CIN concentrations within the range adopted in the food industry were obtained (12.4 ppm). The grafting procedure was also performed on a porous film based on a photocatalytic oxide, demonstrating the versatility of this method, adaptable to both powders and macroscopic materials. By taking advantage of the photoactivity of the oxide, regeneration of the fouled film was achieved upon UV irradiation for 1 h, opening the door to reusable devices for the controlled release of cinnamaldehyde. Full article

(This article belongs to the Special Issue Self-Regulating Materials: Design, Fabrication and Applications)

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23 pages, 13218 KiB

Open AccessEditor’s ChoiceArticle

Structural Response of Steel Jacket-UHPC Retrofitted Reinforced Concrete Columns under Blast Loading

by Mohammad Hanifehzadeh, Hadi Aryan, Bora Gencturk and Dovlet Akyniyazov

Materials 2021, 14(6), 1521; https://doi.org/10.3390/ma14061521 - 20 Mar 2021

Cited by 16 | Viewed by 4467

Abstract

The lateral capacity of exterior concrete columns subjected to a blast load is the key factor in the building collapse probability. Due to potentially severe consequences of the collapse, efforts have been made to improve the blast resistance of existing structures. One of [...] Read more.

The lateral capacity of exterior concrete columns subjected to a blast load is the key factor in the building collapse probability. Due to potentially severe consequences of the collapse, efforts have been made to improve the blast resistance of existing structures. One of the successful approaches is the use of ultra-high-performance-concrete (UHPC) jacketing for retrofitting a building’s columns. The columns on the first floor of a building normally have higher slenderness due to the higher first story. Since an explosion is more likely to take place at the ground level, retrofitting the columns of the lower floors is crucial to improve a building’s blast resistance. Casting a UHPC tube around a circular RC column can increase the moment of inertia of the column and improve the flexural strength. In this study, a retrofitting system consisting of a UHPC layer enclosed by a thin steel jacket is proposed to improve the blast resistance of buildings in service. Most of the previous research is focused on design aspects of blast-resistant columns and retrofitting systems are mostly based on fiber reinforced polymers or steel jackets. A validated FE model is used to investigate the effectiveness of this method. The results showed significant improvement both at the component and building system levels against combined gravity and blast loading. Full article

(This article belongs to the Special Issue Advances in Construction and Building Materials)

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10 pages, 3136 KiB

Open AccessEditor’s ChoiceArticle

Red Y₂O₃:Eu-Based Electroluminescent Device Prepared by Atomic Layer Deposition for Transparent Display Applications

by José Rosa, Mikko J. Heikkilä, Mika Sirkiä and Saoussen Merdes

Materials 2021, 14(6), 1505; https://doi.org/10.3390/ma14061505 - 19 Mar 2021

Cited by 12 | Viewed by 3930

Abstract

Y₂O_3:Eu is a promising red-emitting phosphor owing to its high luminance efficiency, chemical stability, and non-toxicity. Although Y₂O₃:Eu thin films can be prepared by various deposition methods, most of them require high processing temperatures in [...] Read more.

Y₂O_3:Eu is a promising red-emitting phosphor owing to its high luminance efficiency, chemical stability, and non-toxicity. Although Y₂O₃:Eu thin films can be prepared by various deposition methods, most of them require high processing temperatures in order to obtain a crystalline structure. In this work, we report on the fabrication of red Y₂O₃:Eu thin film phosphors and multilayer structure Y₂O₃:Eu-based electroluminescent devices by atomic layer deposition at 300 °C. The structural and optical properties of the phosphor films were investigated using X-ray diffraction and photoluminescence measurements, respectively, whereas the performance of the fabricated device was evaluated using electroluminescence measurements. X-ray diffraction measurements show a polycrystalline structure of the films whereas photoluminescence shows emission above 570 nm. Red electroluminescent devices with a luminance up to 40 cd/m² at a driving frequency of 1 kHz and an efficiency of 0.28 Lm/W were achieved. Full article

(This article belongs to the Special Issue Advanced Luminescent Materials and Devices)

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16 pages, 27277 KiB

Open AccessEditor’s ChoiceArticle

PTFE-Carbon Nanotubes and Lipase B from Candida antarctica—Long-Lasting Marriage for Ultra-Fast and Fully Selective Synthesis of Levulinate Esters

by Anna Szelwicka, Agnieszka Siewniak, Anna Kolanowska, Sławomir Boncel and Anna Chrobok

Materials 2021, 14(6), 1518; https://doi.org/10.3390/ma14061518 - 19 Mar 2021

Cited by 13 | Viewed by 2700

Abstract

An effective method for levulinic acid esters synthesis by the enzymatic Fischer esterification of levulinic acid using a lipase B from Candida antarctica (CALB) immobilized on the advanced material consisting of multi-wall carbon nanotubes (MWCNTs) and a hydrophobic polymer—polytetrafluoroethylene (Teflon, PTFE)—as a heterogeneous [...] Read more.

An effective method for levulinic acid esters synthesis by the enzymatic Fischer esterification of levulinic acid using a lipase B from Candida antarctica (CALB) immobilized on the advanced material consisting of multi-wall carbon nanotubes (MWCNTs) and a hydrophobic polymer—polytetrafluoroethylene (Teflon, PTFE)—as a heterogeneous biocatalyst, was developed. An active phase of the biocatalyst was obtained by immobilization via interfacial activation on the surface of the hybrid material MWCNTs/PTFE (immobilization yield: 6%, activity of CALB: 5000 U∙L∙kg⁻¹, enzyme loading: 22.5 wt.%). The catalytic activity of the obtained biocatalyst and the effects of the selected reaction parameters, including the agitation speed, the amount of PTFE in the CALB/MWCNT-PTFE biocatalyst, the amount of CALB/MWCNT-PTFE, the type of organic solvent, n-butanol excess, were tested in the esterification of levulinic acid by n-butanol. The results showed that the use of a two-fold excess of levulinic acid to n-butanol, 22.5 wt.% of CALB on MWCNT-PTFE (0.10 wt.%) and cyclohexane as a solvent at 20 °C allowed one to obtain n-butyl levulinate with a high yield (99%) and selectivity (>99%) after 45 min. The catalyst retained its activity and stability after three cycles, and then started to lose activity until dropping to a 69% yield of ester in the sixth reaction run. The presented method has opened the new possibilities for environmentally friendly synthesis of levulinate esters. Full article

(This article belongs to the Special Issue Advances in Homogeneous and Heterogeneous Catalysis)

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17 pages, 3200 KiB

Open AccessEditor’s ChoiceArticle

Cement-Matrix Composites Using CFRP Waste: A Circular Economy Perspective Using Industrial Symbiosis

by Pierluca Vitale, Rosanna Napolitano, Francesco Colella, Costantino Menna and Domenico Asprone

Materials 2021, 14(6), 1484; https://doi.org/10.3390/ma14061484 - 18 Mar 2021

Cited by 15 | Viewed by 3454

Abstract

This study aims to provide a mitigation strategy for reducing the economic and environmental impacts of carbon fiber wastes deriving from automotive industry. Recycling and reuse in the construction industry is proposed, according to an industrial symbiosis within a circular economy perspective. Specifically, [...] Read more.

This study aims to provide a mitigation strategy for reducing the economic and environmental impacts of carbon fiber wastes deriving from automotive industry. Recycling and reuse in the construction industry is proposed, according to an industrial symbiosis within a circular economy perspective. Specifically, the process consists of repurposing carbon fiber reinforced polymer (CFRP) scraps/waste into new cement-matrix composites, for which the resulting benefits, in terms of mechanical and environmental performance, are herein described. An experimental campaign, starting with a specific heat treatment of CFRP sheets and an accurate dimensional distribution analysis of the short carbon fibers, is presented. The influence of the fiber content and length on both the workability and the mechanical performance of cement-based carbon fiber reinforced mortars is also evaluated. A reduced amount of either sand or cement (up to 8% and 12.8% in volume, respectively) is also considered in the mix design of the fiber reinforced mortars and derives from the substitution of the sand or binder with an equivalent volume of CFRP fibers. The results show a satisfactory increase in compressive and flexural strength in the range 10–18% for the samples characterized by a volume fraction of fibers of approximately 4% and having a 2–5 mm length. Finally, a life cycle assessment (LCA, 14040/14044) was carried out to quantify the environmental burden reductions associated with the implementation of the proposed symbiotic scheme. Full article

(This article belongs to the Special Issue Recycled Aggregate Concretes: From Raw Materials Selection to Field Applications)

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17 pages, 57598 KiB

Open AccessEditor’s ChoiceArticle

Synthesis and Characterization of Novel Hybrid Flocculants Based on Potato Starch Copolymers with Hollow Carbon Spheres

by Beata Schmidt, Krzysztof Kowalczyk and Beata Zielinska

Materials 2021, 14(6), 1498; https://doi.org/10.3390/ma14061498 - 18 Mar 2021

Cited by 7 | Viewed by 2428

Abstract

Novel carbon nanofiller-based starch-g-polyacrylamide hybrid flocculation materials (St-PAM-CS) were in situ prepared using potato starch (St), acrylamide (AM), and hollow mesoporous carbon spheres (CSs; diameters of 300–400 nm). Structures of different St-PAM-CS systems were characterized by Fourier transform infrared (FTIR) spectroscopy, X-Ray diffraction [...] Read more.

Novel carbon nanofiller-based starch-g-polyacrylamide hybrid flocculation materials (St-PAM-CS) were in situ prepared using potato starch (St), acrylamide (AM), and hollow mesoporous carbon spheres (CSs; diameters of 300–400 nm). Structures of different St-PAM-CS systems were characterized by Fourier transform infrared (FTIR) spectroscopy, X-Ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), laser scanning microscopy (LSM), and particle size analysis. The flocculation tests were evaluated by removing high turbidity kaolin suspension—initial absorbance 1.84. The effect of the St to AM molar ratio, doses, and content of CSs in hybrids on flocculation efficiency were examined. Satisfactory flocculation efficiency was obtained for all hybrids with 1 wt.% of the CS component. The highest reduction of the kaolin suspension absorbance (to 0.06) was observed for a 3 mL dose of the starch hybrid with the highest AM content. Additionally, St-PAM-CS showed a reduction in the sludge volume in time. The hybrids reached better flocculation efficiency in relation to the reference systems without CSs. The proposed flocculation mechanism (considering bridging, patching, and formation of hydrogen bonds) has been confirmed by the recorded results. Full article

(This article belongs to the Special Issue Advanced Eco-Technology and Materials in Water Treatment)

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20 pages, 3219 KiB

Open AccessEditor’s ChoiceArticle

Analytical Model of Two-Directional Cracking Shear-Friction Membrane for Finite Element Analysis of Reinforced Concrete

by Jeffrey P. Mitchell, Bum-Yean Cho and Yoo-Jae Kim

Materials 2021, 14(6), 1460; https://doi.org/10.3390/ma14061460 - 17 Mar 2021

Cited by 1 | Viewed by 2129

Abstract

There are a multitude of existing material models for the finite element analysis of cracked reinforced concrete that provide reduced shear stiffness but do not limit shear strength. In addition, typical models are not based on the actual physical behavior of shear transfer [...] Read more.

There are a multitude of existing material models for the finite element analysis of cracked reinforced concrete that provide reduced shear stiffness but do not limit shear strength. In addition, typical models are not based on the actual physical behavior of shear transfer across cracks by shear friction recognized in the ACI 318 Building Code. A shear-friction model was recently proposed that was able to capture the recognized cracked concrete behavior by limiting shear strength as a yielding function in the reinforcement across the crack. However, the proposed model was formulated only for the specific case of one-directional cracking parallel to the applied shear force. This study proposed and generalized an orthogonal-cracking shear-friction model for finite element use. This was necessary for handling the analysis of complex structures and nonproportional loading cases present in real design and testing situations. This generalized model was formulated as a total strain-based model using the approximation that crack strains are equal to total strains, using the proportional load vector, constant vertical load, and modified Newton–Raphson method to improve the model’s overall accuracy. Full article

(This article belongs to the Special Issue Computational Modelling and Design of Novel Engineering Materials)

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13 pages, 1901 KiB

Open AccessEditor’s ChoiceArticle

Feasible Use of Recycled Concrete Aggregates with Alumina Waste in Road Construction

by Manuel Cabrera, Mónica López-Alonso, Laura Garach, Javier Alegre, Javier Ordoñez and Francisco Agrela

Materials 2021, 14(6), 1466; https://doi.org/10.3390/ma14061466 - 17 Mar 2021

Cited by 5 | Viewed by 2966

Abstract

The management of different industrial by-products, such as recycled aggregates from construction and demolition waste and alumina by-products, as well as the reduction of landfill deposits by incorporating these products in a second life cycle, were the focus of this work. The aim [...] Read more.

The management of different industrial by-products, such as recycled aggregates from construction and demolition waste and alumina by-products, as well as the reduction of landfill deposits by incorporating these products in a second life cycle, were the focus of this work. The aim of this study was to demonstrate the technical viability of using these waste and by-product as a material for road pavement base layers. For this purpose, a real-scale application was carried out, and the behavior of three types of materials, applied on a section of an experimental road under real vehicle traffic conditions, was studied and compared. Three materials were used in these sections applied in the road sub-bases. First, a control material composed of a type of artificial gravel was used to be compared with the rest of materials; the second material was composed of recycled aggregates, and the third was composed of a mix of recycled aggregates and alumina waste. The results concluded that the effectiveness of the sections built using recycled aggregates and alumina waste was very positive and similar those constructed using natural aggregates. Full article

(This article belongs to the Special Issue Properties and Novel Applications of Recycled Concrete and Mixed Aggregates)

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15 pages, 2920 KiB

Open AccessEditor’s ChoiceArticle

Iron Elution from Iron and Steel Slag Using Bacterial Complex Identified from the Seawater

by Hidenori Tsukidate, Seika Otake, Yugo Kato, Ko Yoshimura, Masafumi Kitatsuji, Etsuro Yoshimura and Michio Suzuki

Materials 2021, 14(6), 1477; https://doi.org/10.3390/ma14061477 - 17 Mar 2021

Cited by 4 | Viewed by 2235

Abstract

Iron and steel slag (ISS) is a byproduct of iron refining processes. The lack of iron in seawater can cause barren grounds where algae cannot grow. To improve the barren grounds of the sea, a supply of iron to the seawater is necessary. [...] Read more.

Iron and steel slag (ISS) is a byproduct of iron refining processes. The lack of iron in seawater can cause barren grounds where algae cannot grow. To improve the barren grounds of the sea, a supply of iron to the seawater is necessary. This study focused on bacteria interacting with ISS and promoting iron elution in seawater. Sulfitobacter sp. (TO1A) and Pseudomonas sp. (TO1B) were isolated from Tokyo Bay and Sagami Bay. The co-culture of both bacteria promoted more iron elution than individual cultures. After the incubation of both bacteria with ISS, quartz and vaterite appeared on the surface of the ISS. To maintain continuous iron elution from the ISS in the seawater, we also isolated Pseudoalteromonas sp. (TO7) that formed a yellow biofilm on the ISS. Iron was eluted by TO1A and TO1B, and biofilm was synthesized by TO7 continuously in the seawater. The present research is expected to contribute to the improvement of ISS usage as a material for the construction of seaweed forests. Full article

(This article belongs to the Special Issue Mineralization of Metals through Bio Activities)

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31 pages, 8503 KiB

Open AccessEditor’s ChoiceArticle

Concept of Evaluation of Mineral Additives’ Effect on Cement Pastes’ Durability and Environmental Suitability

by Robert Figmig, Adriana Estokova and Miloslav Luptak

Materials 2021, 14(6), 1448; https://doi.org/10.3390/ma14061448 - 16 Mar 2021

Cited by 7 | Viewed by 2895

Abstract

This experimental study focuses on the assessment of mineral additives and their incorporation into cement composites (CC). The assessment was based on a holistic approach to the performance of the durability properties of CC. Environmental suitability was also taken into consideration. In the [...] Read more.

This experimental study focuses on the assessment of mineral additives and their incorporation into cement composites (CC). The assessment was based on a holistic approach to the performance of the durability properties of CC. Environmental suitability was also taken into consideration. In the experiments, cement pastes with w/c ratios of 0.3, 0.4, and 0.5, respectively, were prepared. Natural zeolite (NZ) and densified silica fume (SF) at doses of 7.5 and 15.0 wt.% of cement were used as the investigated (replacement) materials. Their effects (including development over time) on density, strength (flexural and compressive), porosity by water absorption, permeability by rapid chloride penetration (RCP) test, phase content by thermal analysis, and hydration progression, were observed. The results were then used to propose an evaluation approach. Natural zeolite was used for its known pozzolanic activity and classification as a supplementary cementitious material (SCM). In contrast SF acted as a filler in cement pastes, and thus did not have a direct positive effect on durability. The concept of comprehensive analysis for unknown additive classification is proposed to expressly differentiate between SCM, inert, and improving mineral additive. This concept could be applied to the assessment of mineral additives with regards to the durability and suitability of cement composites. Full article

(This article belongs to the Special Issue Environmentally Friendly Materials in Construction)

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13 pages, 2666 KiB

Open AccessEditor’s ChoiceArticle

Random Material Property Fields of 3D Concrete Microstructures Based on CT Image Reconstruction

by George Stefanou, Dimitrios Savvas and Panagiotis Metsis

Materials 2021, 14(6), 1423; https://doi.org/10.3390/ma14061423 - 15 Mar 2021

Cited by 9 | Viewed by 2380

Abstract

The purpose of this paper is to determine the random spatially varying elastic properties of concrete at various scales taking into account its highly heterogeneous microstructure. The reconstruction of concrete microstructure is based on computed tomography (CT) images of a cubic concrete specimen. [...] Read more.

The purpose of this paper is to determine the random spatially varying elastic properties of concrete at various scales taking into account its highly heterogeneous microstructure. The reconstruction of concrete microstructure is based on computed tomography (CT) images of a cubic concrete specimen. The variability of the local volume fraction of the constituents (pores, cement paste and aggregates) is quantified and mesoscale random fields of the elasticity tensor are computed from a number of statistical volume elements obtained by applying the moving window method on the specimen along with computational homogenization. Based on the statistical characteristics of the mesoscale random fields, it is possible to assess the effect of randomness in microstructure on the mechanical behavior of concrete. Full article

(This article belongs to the Special Issue Computational Materials Modeling, Analysis and Applications)

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18 pages, 3935 KiB

Open AccessEditor’s ChoiceArticle

Encapsulation and Enhanced Release of Resveratrol from Mesoporous Silica Nanoparticles for Melanoma Therapy

by Diogo Marinheiro, Bárbara J. M. L. Ferreira, Párástu Oskoei, Helena Oliveira and Ana L. Daniel-da-Silva

Materials 2021, 14(6), 1382; https://doi.org/10.3390/ma14061382 - 12 Mar 2021

Cited by 52 | Viewed by 4989

Abstract

Chemotherapy has limited success in the treatment of malignant melanoma due to fast development of drug resistance and the low bioavailability of chemotherapeutic drugs. Resveratrol (RES) is a natural polyphenol with recognized preventive and therapeutic anti-cancer properties. However, poor RES solubility hampers its [...] Read more.

Chemotherapy has limited success in the treatment of malignant melanoma due to fast development of drug resistance and the low bioavailability of chemotherapeutic drugs. Resveratrol (RES) is a natural polyphenol with recognized preventive and therapeutic anti-cancer properties. However, poor RES solubility hampers its bioactivity, thus creating a demand for suitable drug delivery systems to improve it. This work aimed to assess the potential of RES-loaded mesoporous silica nanoparticles (MSNs) for human melanoma treatment. RES was efficiently loaded (efficiency > 93%) onto spheroidal (size~60 nm) MSNs. The encapsulation promoted the amorphization of RES and enhanced the release in vitro compared to non-encapsulated RES. The RES release was pH-dependent and markedly faster at pH 5.2 (acid environment in some tumorous tissues) than at pH 7.4 in both encapsulated and bulk forms. The RES release from loaded MSNs was gradual with time, without a burst effect, and well-described by the Weibull model. In vitro cytotoxicity studies on human A375 and MNT-1 melanoma cellular cultures showed a decrease in the cell viability with increasing concentration of RES-loaded MSNs, indicating the potent action of the released RES in both cell lines. The amelanotic cell line A375 was more sensitive to RES concentration than the melanotic MNT-1 cells. Full article

(This article belongs to the Special Issue Novel Engineered Nanomaterials for Advanced Biological Applications)

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20 pages, 3962 KiB

Open AccessEditor’s ChoiceArticle

The Application of Ni–Ti SMA Wires in the External Prestressing of Concrete Hollow Cylinders

by Aleksandra Dębska, Piotr Gwoździewicz, Andrzej Seruga, Xavier Balandraud and Jean-François Destrebecq

Materials 2021, 14(6), 1354; https://doi.org/10.3390/ma14061354 - 11 Mar 2021

Cited by 8 | Viewed by 2269

Abstract

An innovative method for prestressing structural elements through the use of shape memory alloys (SMAs) is gaining increasing attention in research as this method does not require the use of mechanical anchorages for tendons. The activation of the memory effect by means of [...] Read more.

An innovative method for prestressing structural elements through the use of shape memory alloys (SMAs) is gaining increasing attention in research as this method does not require the use of mechanical anchorages for tendons. The activation of the memory effect by means of temperature variations (Joule effect) in effect produces high stresses in SMA components attached to concrete components as reported in the literature. This paper presents the work performed for the purpose of prestressing concrete hollow cylinders with the use of nickel–titanium (Ni–Ti) SMA wires. In the tests, a variety of hollow cylinders were made using the same concrete mix and with the same wall thickness (20 mm), but with different external diameters (200 mm, 250 mm, and 300 mm). Their prestressing was achieved by the means of Ni-Ti SMA wires of different diameters (1 mm, 2 mm, and 3 mm) wrapped around the cylinders. Longitudinal and circumferential strain during the thermal activation of the SMA wires by Joule heating was measured using gauges located on the internal surface of the hollow cylinders. The experimental protocol, recorded observations, and discussion of the effectiveness of the prestressing of concrete elements as a function of the test parameters are included in the text in detail. Comments on the conditions for effective prestressing of concrete cylinders with SMA wires are proposed in the conclusions of the paper. Full article

(This article belongs to the Special Issue Shape Memory Alloys (SMAs) for Engineering Applications)

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18 pages, 9268 KiB

Open AccessEditor’s ChoiceArticle

Surface Modification of Biomedical MgCa_4.5 and MgCa_4.5Gd_0.5 Alloys by Micro-Arc Oxidation

by Piotr Sakiewicz, Krzysztof Piotrowski, Anna Bajorek, Katarzyna Młynarek, Rafał Babilas and Wojciech Simka

Materials 2021, 14(6), 1360; https://doi.org/10.3390/ma14061360 - 11 Mar 2021

Cited by 7 | Viewed by 2235

Abstract

The aim of this work was to characterize the structure and corrosion properties of the MgCa_4.5(Gd_0.5) alloys surface treated by the micro-arc oxidation (MAO) process. The MgCa_4.5 and MgCa_4.5Gd_0.5 alloy samples were processed by MAO [...] Read more.

The aim of this work was to characterize the structure and corrosion properties of the MgCa_4.5(Gd_0.5) alloys surface treated by the micro-arc oxidation (MAO) process. The MgCa_4.5 and MgCa_4.5Gd_0.5 alloy samples were processed by MAO in an electrolyte composed of NaOH (10 g/dm³), NaF (10 g/dm³), NaH₂PO₄ (5 g/dm³), Na₂SiO₂·5H₂O (10 g/dm³) and water. Two different voltages (120 V and 140 V) were used in the MAO process. The alloys protected by an oxide layer formed in the MAO were then the subject of corrosion resistance tests in an environment simulating the human body (Ringer’s solution). After the experiments, the resulting samples were investigated using SEM, XPS and EDS techniques. The addition of Gd affected the fragmentation of the coating structure, thereby increasing the specific surface; higher voltages during the MAO process increased the number and size of surface pores. Corrosion tests showed that the MgCa_4.5Gd_0.5 alloys were characterized by low polarization resistances and high corrosion current densities. The studies indicated the disadvantageous influence of gadolinium on the corrosion resistance of MgCa_4.5 alloys. The immersion tests confirmed lower corrosion resistance of MgCa_4.5Gd_0.5 alloys compared to the referenced MgCa_4.5 ones. The MgCa_4.5 alloy with the MAO coating established at voltage 140 V demonstrated the best anticorrosion properties. Full article

(This article belongs to the Special Issue Structure and Properties of Crystalline and Amorphous Alloys)

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11 pages, 1683 KiB

Open AccessEditor’s ChoiceArticle

Closed-Surface Multifunctional Antireflective Coating Made from SiO₂ with TiO₂ Nanocomposites

by Zhiqiu Guo, Ze Zhu, Ya Liu, Changjun Wu, Hao Tu, Jianhua Wang and Xuping Su

Materials 2021, 14(6), 1367; https://doi.org/10.3390/ma14061367 - 11 Mar 2021

Cited by 10 | Viewed by 2801

Abstract

An SiO₂-TiO₂ closed-surface antireflective coating was fabricated by the one-dipping method. TiO₂ nanoparticles were mixed with a nanocomposited silica sol, which was composed of acid-catalyzed nanosilica networks and silica hollow nanospheres (HNs). The microstructure of the sol-gel was characterized [...] Read more.

An SiO₂-TiO₂ closed-surface antireflective coating was fabricated by the one-dipping method. TiO₂ nanoparticles were mixed with a nanocomposited silica sol, which was composed of acid-catalyzed nanosilica networks and silica hollow nanospheres (HNs). The microstructure of the sol-gel was characterized by transmission electron microscopy. The silica HNs were approximately 40–50 nm in diameter with a shell thickness of approximately 8–10 nm. The branched-chain structure resulting from acidic hydrolysis grew on these silica HNs, and TiO₂ was distributed inside this network. The surface morphology of the coating was measured by field emission scanning electron microscopy and atomic force microscopy. After optimization, transmittance of up to 94.03% was obtained on photovoltaic (PV) glass with a single side coated by this antireflective coating, whose refractive index was around 1.30. The short-circuit current gain of PV module was around 2.14–2.32%, as shown by the current-voltage (IV) curve measurements and external quantum efficiency (EQE) tests. This thin film also exhibited high photocatalytic activity. Due to the lack of voids on its surface, the antireflective coating in this study possessed excellent long-term reliability and robustness in both high-moisture and high-temperature environments. Combined with its self-cleaning function, this antireflective coating has great potential to be implemented in windows and photovoltaic modules. Full article

(This article belongs to the Section Thin Films and Interfaces)

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23 pages, 74030 KiB

Open AccessEditor’s ChoiceArticle

A Method for Evaluation the Fatigue Microcrack Propagation in Human Cortical Bone Using Differential X-ray Computed Tomography

by Petr Koudelka, Daniel Kytyr, Tomas Fila, Jan Sleichrt, Vaclav Rada, Petr Zlamal, Pavel Benes, Vendula Bendova, Ivana Kumpova and Michal Vopalensky

Materials 2021, 14(6), 1370; https://doi.org/10.3390/ma14061370 - 11 Mar 2021

Cited by 4 | Viewed by 2825

Abstract

Fatigue initiation and the propagation of microcracks in a cortical bone is an initial phase of damage development that may ultimately lead to the formation of macroscopic fractures and failure of the bone. In this work, a time-resolved high-resolution X-ray micro-computed tomography (CT) [...] Read more.

Fatigue initiation and the propagation of microcracks in a cortical bone is an initial phase of damage development that may ultimately lead to the formation of macroscopic fractures and failure of the bone. In this work, a time-resolved high-resolution X-ray micro-computed tomography (CT) was performed to investigate the system of microcracks in a bone sample loaded by a simulated gait cycle. A low-cycle (1000 cycles) fatigue loading in compression with a 900 N peak amplitude and a 0.4 Hz frequency simulating the slow walk for the initialization of the internal damage of the bone was used. An in-house developed laboratory X-ray micro-CT imaging system coupled with a compact loading device were employed for the in situ uni-axial fatigue experiments reaching a μ

2 μ m

effective voxel size. To reach a comparable quality of the reconstructed 3D images with the SEM microscopy, projection-level corrections and focal spot drift correction were performed prior to the digital volume correlation and evaluation using differential tomography for the identification of the individual microcracks in the microstructure. The microcracks in the intact bone, the crack formation after loading, and the changes in the topology of the microcracks were identified on a volumetric basis in the microstructure of the bone. Full article

(This article belongs to the Special Issue 4D X-ray Computed Tomography for Material Science)

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25 pages, 8213 KiB

Open AccessEditor’s ChoiceArticle

Thermodynamic Modelling and Microstructural Study of Z-Phase Formation in a Ta-Alloyed Martensitic Steel

by Florian Riedlsperger, Bernadette Gsellmann, Erwin Povoden-Karadeniz, Oriana Tassa, Susanna Matera, Mária Dománková, Florian Kauffmann, Ernst Kozeschnik and Bernhard Sonderegger

Materials 2021, 14(6), 1332; https://doi.org/10.3390/ma14061332 - 10 Mar 2021

Cited by 3 | Viewed by 3545

Abstract

A thermokinetic computational framework for precipitate transformation simulations in Ta-containing martensitic Z-steels was developed, including Calphad thermodynamics, diffusion mobility data from the literature, and a kinetic parameter setup that considered precipitation sites, interfacial energies and dislocation density evolution. The thermodynamics of Ta-containing subsystems [...] Read more.

A thermokinetic computational framework for precipitate transformation simulations in Ta-containing martensitic Z-steels was developed, including Calphad thermodynamics, diffusion mobility data from the literature, and a kinetic parameter setup that considered precipitation sites, interfacial energies and dislocation density evolution. The thermodynamics of Ta-containing subsystems were assessed by atomic solubility data and enthalpies from the literature as well as from the experimental dissolution temperature of Ta-based Z-phase CrTaN obtained from differential scanning calorimetry. Accompanied by a comprehensive transmission electron microscopy analysis of the microstructure, thermokinetic precipitation simulations with a wide-ranging and well-documented set of input parameters were carried out in MatCalc for one sample alloy. A special focus was placed on modelling the transformation of MX into the Z-phase, which was driven by Cr diffusion. The simulation results showed excellent agreement with experimental data in regard to size, number density and chemical composition of the precipitates, showing the usability of the developed thermokinetic simulation framework. Full article

(This article belongs to the Special Issue Creep and High Temperature Deformation of Steels and Alloys)

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10 pages, 3190 KiB

Open AccessEditor’s ChoiceArticle

Carbon Dot/Naphthalimide Based Ratiometric Fluorescence Biosensor for Hyaluronidase Detection

by Pushap Raj, Seon-yeong Lee and Tae Yoon Lee

Materials 2021, 14(5), 1313; https://doi.org/10.3390/ma14051313 - 9 Mar 2021

Cited by 27 | Viewed by 3619

Abstract

Bladder cancer is the leading cause of death in patients with genitourinary cancer. An elevated level of hyaluronidase (HAase) was found in bladder cancer, which acts as an important biomarker for the early diagnosis of bladder cancer. Hence, there is a need to [...] Read more.

Bladder cancer is the leading cause of death in patients with genitourinary cancer. An elevated level of hyaluronidase (HAase) was found in bladder cancer, which acts as an important biomarker for the early diagnosis of bladder cancer. Hence, there is a need to develop a simple enzymatic assay for the early recognition of HAase. Herein, we report a simple, sensitive, and ratiometric fluorescence assay for HAase detection under physiological conditions. The fluorescence assay was constructed by the adsorption of cationic carbon dots and positively charged naphthalimide on negatively charged hyaluronic acid and the development of a Förster resonance energy transfer (FRET) mechanism from carbon dots to a naphthalimide fluorophores. The hyaluronidase enzyme cleaves the hyaluronic acid in this assay, and breaking down the FRET mechanism induces ratiometric changes. A detection limit of 0.09 U/mL was achieved, which is less than the HAase level found in normal human body fluids. Moreover, this assay may be used for diagnosing HAase-related diseases. Full article

(This article belongs to the Special Issue Soft Materials and Optical Devices)

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22 pages, 2954 KiB

Open AccessEditor’s ChoiceReview

Applications of Additively Manufactured Tools in Abrasive Machining—A Literature Review

by Mariusz Deja, Dawid Zieliński, Aini Zuhra Abdul Kadir and Siti Nur Humaira

Materials 2021, 14(5), 1318; https://doi.org/10.3390/ma14051318 - 9 Mar 2021

Cited by 34 | Viewed by 5587

Abstract

High requirements imposed by the competitive industrial environment determine the development directions of applied manufacturing methods. 3D printing technology, also known as additive manufacturing (AM), currently being one of the most dynamically developing production methods, is increasingly used in many different areas of [...] Read more.

High requirements imposed by the competitive industrial environment determine the development directions of applied manufacturing methods. 3D printing technology, also known as additive manufacturing (AM), currently being one of the most dynamically developing production methods, is increasingly used in many different areas of industry. Nowadays, apart from the possibility of making prototypes of future products, AM is also used to produce fully functional machine parts, which is known as Rapid Manufacturing and also Rapid Tooling. Rapid Manufacturing refers to the ability of the software automation to rapidly accelerate the manufacturing process, while Rapid Tooling means that a tool is involved in order to accelerate the process. Abrasive processes are widely used in many industries, especially for machining hard and brittle materials such as advanced ceramics. This paper presents a review on advances and trends in contemporary abrasive machining related to the application of innovative 3D printed abrasive tools. Examples of abrasive tools made with the use of currently leading AM methods and their impact on the obtained machining results were indicated. The analyzed research works indicate the great potential and usefulness of the new constructions of the abrasive tools made by incremental technologies. Furthermore, the potential and limitations of currently used 3D printed abrasive tools, as well as the directions of their further development are indicated. Full article

(This article belongs to the Special Issue Precision and Ultra-Precision Subtractive and Additive Manufacturing Processes of Alloys and Steels)

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11 pages, 2776 KiB

Open AccessEditor’s ChoiceArticle

Chemical Modification of B₄C Films and B₄C/Pd Layers Stored in Different Environments

by Yufei Feng, Runze Qi, Li Jiang, Qiushi Huang, Tongzhou Li, Genchang Liu, Wenbin Li, Wensheng Yan, Zhong Zhang and Zhanshan Wang

Materials 2021, 14(5), 1319; https://doi.org/10.3390/ma14051319 - 9 Mar 2021

Cited by 20 | Viewed by 3028

Abstract

B₄C/Pd multilayers with small d-spacing can easily degrade in the air, and the exact degradation process is not clear. In this work, we studied the chemical modification of B₄C films and B₄C/Pd double layers stored in four [...] Read more.

B₄C/Pd multilayers with small d-spacing can easily degrade in the air, and the exact degradation process is not clear. In this work, we studied the chemical modification of B₄C films and B₄C/Pd double layers stored in four different environments: a dry nitrogen environment, the atmosphere, a dry oxygen-rich environment, and a wet nitrogen environment. The XANES spectra of the B₄C/Pd layers placed in a dry oxygen-rich environment showed the most significant decrease in the σ* states of the B–C bonds and an increase in the π* states of the B–O bonds compared with the other samples. X-ray photoelectron spectroscopy (XPS) measurements of the samples placed in a dry oxygen-rich environment showed more intensive B-O binding signals in the B₄C/Pd layers than in the single B₄C film. The results of the Fourier-transform infrared spectroscopy (FTIR) showed a similar decrease in the B–C bonds and an increase in the B–O bonds in the B₄C/Pd layers in contrast to the single B₄C film placed in a dry oxygen-rich environment. We concluded that the combination of palladium catalysis and the high content of oxygen in the environment promoted the oxidization of boron, deteriorated the B₄C composition. Full article

(This article belongs to the Section Materials Physics)

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12 pages, 4500 KiB

Open AccessEditor’s ChoiceArticle

Electromagnetic Shielding Properties of Knitted Fabric Made from Polyamide Threads Coated with Silver

by Tanja Pušić, Bosiljka Šaravanja and Krešimir Malarić

Materials 2021, 14(5), 1281; https://doi.org/10.3390/ma14051281 - 8 Mar 2021

Cited by 21 | Viewed by 3982

Abstract

This paper investigates a textile material of low surface mass for its protection against electromagnetic radiation (EMR), which is suitable for composite structures of garments, and for technical and interior applications. The shielding effectiveness against EMR of fabric knitted from polyamide threads coated [...] Read more.

This paper investigates a textile material of low surface mass for its protection against electromagnetic radiation (EMR), which is suitable for composite structures of garments, and for technical and interior applications. The shielding effectiveness against EMR of fabric knitted from polyamide threads coated with silver, measured in the frequency range of 0.9 GHz to 2.4 GHz, indicated a high degree of protection. The key contribution of the paper is the evaluation of the stability of the shielding properties against EM radiation after applying apolar and polar solvents, in synergy with the cyclic process parameters of wet and dry cleaning. The results of the study confirmed the decline in the shielding effectiveness after successive cycles of material treatment with dry and wet cleaning. The effect of wet cleaning in relation to dry cleaning is more apparent, which is due to the damage of the silver coating on the polyamide threads in the knitted fabric. Full article

(This article belongs to the Special Issue Advanced Materials for Clothing and Textile Engineering)

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11 pages, 4656 KiB

Open AccessEditor’s ChoiceArticle

Asymmetrical Barkhausen Noise of a Hard Milled Surface

by Mária Čilliková, Anna Mičietová, Robert Čep, Branislav Mičieta, Miroslav Neslušan and Pavel Kejzlar

Materials 2021, 14(5), 1293; https://doi.org/10.3390/ma14051293 - 8 Mar 2021

Cited by 8 | Viewed by 2103

Abstract

This study is focused on the asymmetrical Barkhausen noise emission of a hard milled surface during cyclic magnetisation. The Barkhausen noise is studied as a function of the magnetising voltage and the hard milled surface is compared with a surface after heat treatment. [...] Read more.

This study is focused on the asymmetrical Barkhausen noise emission of a hard milled surface during cyclic magnetisation. The Barkhausen noise is studied as a function of the magnetising voltage and the hard milled surface is compared with a surface after heat treatment. The asymmetry in the Barkhausen noise emission after hard milling occurs due to the typical “sandwich” structure and the different magnetic hardnesses of the different layers beneath the free surface. Furthermore, this asymmetry is also due to the preferential orientation of the matrix in the direction of the cutting speed and magnetostatic fields, which hinder or favour the premagnetising process. Full article

(This article belongs to the Collection Machining and Manufacturing of Alloys and Steels)

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18 pages, 8207 KiB

Open AccessEditor’s ChoiceArticle

Preliminary Studies of the Durability of Tools Used to Form Ceramic Tiles Made of Hardox 600 and NC11LV Steel

by Jan Marzec, Marek Hawryluk, Marcin Rychlik, Marzena M. Lachowicz and Maciej Suliga

Materials 2021, 14(5), 1262; https://doi.org/10.3390/ma14051262 - 7 Mar 2021

Cited by 4 | Viewed by 2363

Abstract

The study performs a comparative analysis of the wear of tools made of two wear-resistant materials: steel Hardox 600 and NC11LV, used in the process of forming a band for roofing tiles. The analyses were to allow the assessment of the possibility of [...] Read more.

The study performs a comparative analysis of the wear of tools made of two wear-resistant materials: steel Hardox 600 and NC11LV, used in the process of forming a band for roofing tiles. The analyses were to allow the assessment of the possibility of replacing the standard material for tools in this process with a much less expensive tool steel for cold work after heat treatment (with a large number of carbides), as an alternative material dedicated to tools resistant to intense abrasive wear. The performed investigations included a macroscopic and geometrical analysis with the use of 3D scanning, microstructural analyses conducted by means of a light microscope, as well as an analysis of the topography of the working areas of the tools with the use of SEM, and microhardness tests. The obtained results demonstrate that the tools made of both materials were characterized with a similar level of wear, which, in the most critical area, reached over 4 mm, while the tools made of steel NC11LV worked over a much longer period of time without regeneration, equaling 912 h, and an insert made of steel Hardox 600 operated for 384 h. A higher tool life in the case of NC11LV steel may be the result of higher hardness and the presence of hard carbides. Full article

(This article belongs to the Special Issue Tribology: Friction and Wear of Engineering Materials)

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12 pages, 22648 KiB

Open AccessEditor’s ChoiceArticle

Extended Hückel Semi-Empirical Approach as an Efficient Method for Structural Defects Analysis in 4H-SiC

by Janusz Wozny, Andrii Kovalchuk, Jacek Podgorski and Zbigniew Lisik

Materials 2021, 14(5), 1247; https://doi.org/10.3390/ma14051247 - 6 Mar 2021

Cited by 3 | Viewed by 2685

Abstract

This paper presents an efficient method to calculate the influence of structural defects on the energy levels and energy band-gap for the 4H-SiC semiconductor. The semi-empirical extended Hückel method was applied to both ideal 4H-SiC crystal and different structures with defects like vacancies, [...] Read more.

This paper presents an efficient method to calculate the influence of structural defects on the energy levels and energy band-gap for the 4H-SiC semiconductor. The semi-empirical extended Hückel method was applied to both ideal 4H-SiC crystal and different structures with defects like vacancies, stacking faults, and threading edge dislocations. The Synopsys QuatumATK package was used to perform the simulations. The results are in good agreement with standard density functional theory (DFT) methods and the computing time is much lower. This means that a structure with ca. 1000 atoms could be easily modeled on typical computing servers within a few hours of computing time, enabling fast and accurate simulation of non-ideal atomic structures. Full article

(This article belongs to the Special Issue SiC Materials and Applications)

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8 pages, 1483 KiB

Open AccessEditor’s ChoiceCommunication

Short-Term Impact of AC Harmonics on Aging of NiMH Batteries for Grid Storage Applications

by Jenny Börjesson Axén, Rudi Soares, Oskar Wallmark, Peter Thelin, Erika Widenkvist Zetterström and Göran Lindbergh

Materials 2021, 14(5), 1248; https://doi.org/10.3390/ma14051248 - 6 Mar 2021

Cited by 2 | Viewed by 2628

Abstract

Batteries in energy storage systems are exposed to electrical noise, such as alternating current (AC) harmonics. While there have been many studies investigating whether Lithium-ion batteries are affected by AC harmonics, such studies on Nickel Metal Hydride (NiMH) batteries are scarce. In this [...] Read more.

Batteries in energy storage systems are exposed to electrical noise, such as alternating current (AC) harmonics. While there have been many studies investigating whether Lithium-ion batteries are affected by AC harmonics, such studies on Nickel Metal Hydride (NiMH) batteries are scarce. In this study a 10 Ah, 12 V NiMH battery was tested with three different harmonic current frequency overlays during a single charge/discharge cycle: 50 Hz, 100 Hz, and 1000 Hz. No effect on battery internal temperature or gas pressure was found, indicating that NiMH battery aging is not affected by the tested harmonic AC frequencies. This can reduce the cost of energy storage systems, as no extra filters are needed to safeguard the batteries. Instead, the capacitive properties of the batteries give the possibility to use the battery bank itself as a high pass filter, further reducing system complexity and cost. Full article

(This article belongs to the Special Issue Hydrogen Storage: Materials, Methods and Perspectives)

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21 pages, 4139 KiB

Open AccessEditor’s ChoiceArticle

Experimental Study on Biaxial Dynamic Compressive Properties of ECC

by Shuling Gao and Guanhua Hu

Materials 2021, 14(5), 1257; https://doi.org/10.3390/ma14051257 - 6 Mar 2021

Cited by 6 | Viewed by 2585

Abstract

An improved hydraulic servo structure testing machine has been used to conduct biaxial dynamic compression tests on eight types of engineered cementitious composites (ECC) with lateral pressure levels of 0, 0.125, 0.25, 0.5, 0.7, 0.8, 0.9, 1.0 (the ratio of the compressive strength [...] Read more.

An improved hydraulic servo structure testing machine has been used to conduct biaxial dynamic compression tests on eight types of engineered cementitious composites (ECC) with lateral pressure levels of 0, 0.125, 0.25, 0.5, 0.7, 0.8, 0.9, 1.0 (the ratio of the compressive strength applied laterally to the static compressive strength of the specimen), and three strain rates of 10⁻⁴, 10⁻³ and 10⁻² s⁻¹. The failure mode, peak stress, peak strain, deformation modulus, stress-strain curve, and compressive toughness index of ECC under biaxial dynamic compressive stress state are obtained. The test results show that the lateral pressure affects the direction of ECC cracking, while the strain rate has little effect on the failure morphology of ECC. The growth of lateral pressure level and strain rate upgrades the limit failure strength and peak strain of ECC, and the small improvement is achieved in elastic modulus. A two-stage ECC biaxial failure strength standard was established, and the influence of the lateral pressure level and peak strain was quantitatively evaluated through the fitting curve of the peak stress, peak strain, and deformation modulus of ECC under various strain rates and lateral pressure levels. ECC’s compressive stress-strain curve can be divided into four stages, and a normalized biaxial dynamic ECC constitutive relationship is established. The toughness index of ECC can be increased with the increase of lateral pressure level, while the increase of strain rate can reduce the toughness index of ECC. Under the effect of biaxial dynamic load, the ultimate strength of ECC is increased higher than that of plain concrete. Full article

(This article belongs to the Special Issue Advances in Cement-Based Materials: Mechanical Behavior, Rheology, and Radiology)

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15 pages, 4964 KiB

Open AccessEditor’s ChoiceArticle

Analysis of Acoustic Emission Signals Recorded during Freeze-Thaw Cycling of Concrete

by Libor Topolář, Dalibor Kocáb, Luboš Pazdera and Tomáš Vymazal

Materials 2021, 14(5), 1230; https://doi.org/10.3390/ma14051230 - 5 Mar 2021

Cited by 11 | Viewed by 2659

Abstract

This manuscript deals with a complex analysis of acoustic emission signals that were recorded during freeze-thaw cycles in test specimens produced from air-entrained concrete. An assessment of the resistance of concrete to the effects of freezing and thawing was conducted on the basis [...] Read more.

This manuscript deals with a complex analysis of acoustic emission signals that were recorded during freeze-thaw cycles in test specimens produced from air-entrained concrete. An assessment of the resistance of concrete to the effects of freezing and thawing was conducted on the basis of a signal analysis. Since the experiment simulated testing of concrete in a structure, a concrete block with the height of 2.4 m and width of 1.8 m was produced to represent a real structure. When the age of the concrete was two months, samples were obtained from the block by core drilling and were subsequently used to produce test specimens. Testing of freeze-thaw resistance of concrete employed both destructive and non-destructive methods including the measurement of acoustic emission, which took place directly during the freeze-thaw cycles. The recorded acoustic emission signals were then meticulously analysed. The aim of the conducted experiments was to verify whether measurement using the acoustic emission method during Freeze-thaw (F-T) cycles are more sensitive to the degree of damage of concrete than the more commonly employed construction testing methods. The results clearly demonstrate that the acoustic emission method can reveal changes (e.g., minor cracks) in the internal structure of concrete, unlike other commonly used methods. The analysis of the acoustic emission signals using a fast Fourier transform revealed a significant shift of the dominant frequency towards lower values when the concrete was subjected to freeze-thaw cycling. Full article

(This article belongs to the Special Issue Testing of Materials and Elements in Civil Engineering)

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24 pages, 14517 KiB

Open AccessEditor’s ChoiceArticle

Microstructures and Mechanical Properties of Deposited Fe-8Cr-3V-2Mo-2W on SCM420 Substrate Using Directed Energy Deposition and Effect of Post-Heat Treatment

by Ye Eun Jeong, Jun Yeop Lee, Eun Kyung Lee and Do Sik Shim

Materials 2021, 14(5), 1231; https://doi.org/10.3390/ma14051231 - 5 Mar 2021

Cited by 9 | Viewed by 3273

Abstract

In this study, the Fe-8Cr-3V-2Mo-2W tool steel powder was deposited on the SCM420 substrate through the directed energy deposition (DED) process. This study focuses on the mechanical properties of the deposited Fe-8Cr-3V-2Mo-2W and the effect of heat treatment on it. The changes in [...] Read more.

In this study, the Fe-8Cr-3V-2Mo-2W tool steel powder was deposited on the SCM420 substrate through the directed energy deposition (DED) process. This study focuses on the mechanical properties of the deposited Fe-8Cr-3V-2Mo-2W and the effect of heat treatment on it. The changes in the microstructural characteristics of the deposited region due to heat treatment after deposition were observed. The influence of heat treatment on the mechanical properties was then analyzed accordingly and hence, the hardness, wear, impact and tensile tests were conducted on the deposited material. These properties were compared with those of the commercial tool steel powder M2-deposited material and the carburized specimen. In the deposited Fe-8Cr-3V-2Mo-2W layer, an increased martensite phase fraction was obtained through post-heat treatment and the amount of precipitated carbides was also increased. This increased the hardness from 48 to 62 HRc after heat treatment and the wear resistance was significantly improved as well. The amount of impact energy absorbed decreased from 11 J before heat treatment to 6 J after heat treatment, but the tensile strength significantly increased from 607 to 922 MPa. When compared with the M2-deposited surface, the Fe-8Cr-3V-2Mo-2W deposits had 3% lower surface hardness and 76% lower fracture toughness but exhibited 56% higher tensile strength. When compared with the carburized SCM420, the Fe-8Cr-3V-2Mo-2W deposits exhibited 3% higher surface hardness and wear resistance, 90% lower fracture toughness and 5% higher tensile strength. This study shows that surface hardening through DED can exhibit similar or superior mechanical properties when compared to carburizing. Full article

(This article belongs to the Special Issue Additive Manufacturing Technologies and Its Applications Using Advanced Materials)

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8 pages, 2495 KiB

Open AccessEditor’s ChoiceCommunication

Polarization-Sensitive Light Sensors Based on a Bulk Perovskite MAPbBr₃ Single Crystal

by Yuan Wang, Laipan Zhu and Cuifeng Du

Materials 2021, 14(5), 1238; https://doi.org/10.3390/ma14051238 - 5 Mar 2021

Cited by 5 | Viewed by 2804

Abstract

Organic-inorganic halide perovskites have attracted much attention thanks to their excellent optoelectronic performances. Here, a bulk CH₃NH₃PbBr₃ (MAPbBr₃) single crystal (SC) was fabricated, whose temperature and light polarization dependence was investigated by measuring photoluminescence. The presence [...] Read more.

Organic-inorganic halide perovskites have attracted much attention thanks to their excellent optoelectronic performances. Here, a bulk CH₃NH₃PbBr₃ (MAPbBr₃) single crystal (SC) was fabricated, whose temperature and light polarization dependence was investigated by measuring photoluminescence. The presence of obvious band tail states was unveiled when the applied temperature was reduced from room temperature to 78 K. Temperature dependence of the bandgap of the MAPbBr₃ SC was found to be abnormal compared with those of traditional semiconductors due to the presence of instabilization of out-of-phase tail states. The MAPbBr₃ SC revealed an anisotropy light absorption for linearly polarized light with an anisotropy ratio of 1.45, and a circular dichroism ratio of up to 9% was discovered due to the spin-orbit coupling in the band tail states, exhibiting great polarization sensitivity of the MAPbBr₃ SC for the application of light sensors. These key findings shed light on the development of potential optoelectronic and spintronic applications based on large-scaled organic-inorganic perovskite SCs. Full article

(This article belongs to the Special Issue Advances in Smart Materials and Self-Powered Nanogenerators Systems)

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18 pages, 16588 KiB

Open AccessEditor’s ChoiceArticle

Utilization of Rice Husk Ash in the Preparation of Graphene-Oxide-Based Mesoporous Nanocomposites with Excellent Adsorption Performance

by Tzong-Horng Liou and Yuan Hao Liou

Materials 2021, 14(5), 1214; https://doi.org/10.3390/ma14051214 - 4 Mar 2021

Cited by 31 | Viewed by 3934

Abstract

Rice husk is an agricultural biomass waste. Burning rice husks in an oxygenic atmosphere releases thermal energy and produces ash that is rich in silica. Rice husk ash (RHA) can be used as a sustainable source of silica for producing high-value-added products. In [...] Read more.

Rice husk is an agricultural biomass waste. Burning rice husks in an oxygenic atmosphere releases thermal energy and produces ash that is rich in silica. Rice husk ash (RHA) can be used as a sustainable source of silica for producing high-value-added products. In this study, mesostructural graphene oxide (GO)/SBA-15, a graphene-based hybrid material, was synthesized from RHA. The materials are inspected by Fourier transform infrared spectrometer, Raman spectrometer, field-emission scanning electron microscopy, transmission electron microscopy, surface area analyzer, and X-ray diffraction analyzer. Studies have revealed that GO/SBA-15 possesses various oxygen functional groups that are helpful for dye adsorption. The material consisted of high pore volume of 0.901 cm³/g, wide pores of diameter 11.67 nm, and high surface area of 499 m²/g. Analysis of the methylene blue (MB) adsorption behavior of GO/SBA-15 composites revealed that their adsorption capacity depended on the gelation pH, GO content, adsorbent dosage, and initial dye (MB) concentration. The highest adsorption capacity of GO/SBA-15 was 632.9 mg/g. Furthermore, the adsorption isotherms and kinetics of GO/SBA-15 were investigated. This study demonstrated the great advantage of treated RHA and the potential of this material for use in organic dye adsorption. Full article

(This article belongs to the Special Issue Adsorbents and Their Applications)

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16 pages, 6122 KiB

Open AccessEditor’s ChoiceArticle

Application of Innovative Ropes from Textile Waste as an Anti-Erosion Measure

by Giang Nguyen, Joanna Grzybowska-Pietras and Jan Broda

Materials 2021, 14(5), 1179; https://doi.org/10.3390/ma14051179 - 3 Mar 2021

Cited by 7 | Viewed by 2762

Abstract

Using materials from recycling is a key part of decreasing present-day waste. It is optimal for recycled material to be used in environmental protection. This paper presents the application of geotextile ropes in erosion protection of a slope of a gravel pit. To [...] Read more.

Using materials from recycling is a key part of decreasing present-day waste. It is optimal for recycled material to be used in environmental protection. This paper presents the application of geotextile ropes in erosion protection of a slope of a gravel pit. To protect the slope, thick ropes with a diameter of 120 mm made from wool and a mixture of recycled natural and synthetic fibers were used. After 47 months from installation, soil and rope specimens were taken from the slope parts with inclinations 1:1 and 1:1.8, and their physical and mechanical properties were determined. Direct shear tests were applied to determine the soil shear strength parameters in state at sampling and at I_c = 0 (unconsolidated and consolidated). Based on the obtained soil shear strength parameters, the loads on the ropes were determined, taking into account also unfavorable hydraulic conditions and compared to rope strength. It was shown that even after 47 months from installation, rope tension strength was higher as tension forces were induced in the ropes in every case. At present, whole slopes in protected sections are stabilized, without rills and gullies. Full article

(This article belongs to the Special Issue Innovative Materials in the Building Industry: Reducing Building Energy and Minimising Environmental Impacts)

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13 pages, 6748 KiB

Open AccessEditor’s ChoiceArticle

Improvement of Corrosion Resistance of TiO₂ Layers in Strong Acidic Solutions by Anodizing and Thermal Oxidation Treatment

by Badar Minhas, Sahib Dino, Yu Zuo, Hongchang Qian and Xuhui Zhao

Materials 2021, 14(5), 1188; https://doi.org/10.3390/ma14051188 - 3 Mar 2021

Cited by 17 | Viewed by 3782

Abstract

By anodization and thermal oxidation at 600 °C, an oxide layer on Ti with excellent corrosion resistance in strong acid solutions was prepared. The structural properties of TiO₂ films before and after thermal oxidation were investigated with methods of Scanning electron microscope [...] Read more.

By anodization and thermal oxidation at 600 °C, an oxide layer on Ti with excellent corrosion resistance in strong acid solutions was prepared. The structural properties of TiO₂ films before and after thermal oxidation were investigated with methods of Scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The electrochemical characterization was recorded via electrochemical impedance spectroscopy, potentiodynamic polarization and Mott–Schottky methods. XRD results show that a duplex rutile/anatase structure formed after oxidation, and the amount of anatase phase increased as the treatment time was prolonged from 3 to 9 h. XPS analysis indicates that as the thermal oxidation time increased, more Ti vacancies were present in the titanium oxide films, with decreased donor concentration. Longer thermal oxidation promoted the formation of hydroxides of titanium on the surface, which is helpful to improve the passive ability of the film. The anodized and thermally oxidized Ti samples showed relatively high corrosion resistance in 4 M HCl and 4 M H₂SO₄ solutions at 100 ± 5 °C. The passive current density values of the thermally oxidized samples were five orders of magnitude under the testing condition compared with that of the anodized sample. With the oxidation time prolonged, the passive current density decreased further to some extent. Full article

(This article belongs to the Special Issue Development of Mechanical, Corrosion Resistance, and Antibacterial Properties of Steels)

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26 pages, 42421 KiB

Open AccessEditor’s ChoiceArticle

Lab-Scale Study of Temperature and Duration Effects on Carbonized Solid Fuels Properties Produced from Municipal Solid Waste Components

by Kacper Świechowski, Paweł Stępień, Ewa Syguła, Jacek A. Koziel and Andrzej Białowiec

Materials 2021, 14(5), 1191; https://doi.org/10.3390/ma14051191 - 3 Mar 2021

Cited by 12 | Viewed by 2934

Abstract

In work, data from carbonization of the eight main municipal solid waste components (carton, fabric, kitchen waste, paper, plastic, rubber, paper/aluminum/polyethylene (PAP/AL/PE) composite packaging pack, wood) carbonized at 300–500 °C for 20–60 min were used to build regression models to predict the biochar [...] Read more.

In work, data from carbonization of the eight main municipal solid waste components (carton, fabric, kitchen waste, paper, plastic, rubber, paper/aluminum/polyethylene (PAP/AL/PE) composite packaging pack, wood) carbonized at 300–500 °C for 20–60 min were used to build regression models to predict the biochar properties (proximate and ultimate analysis) for particular components. These models were then combined in general models that predict the properties of char made from mixed waste components depending on pyrolysis temperature, residence time, and share of municipal solid waste components. Next, the general models were compared with experimental data (two mixtures made from the above-mentioned components carbonized at the same conditions). The comparison showed that most of the proposed general models had a determination coefficient (R²) over 0.6, and the best prediction was found for the prediction of biochar mass yield (R² = 0.9). All models were implemented into a spreadsheet to provide a simple tool to determine the potential of carbonization of municipal solid waste/refuse solid fuel based on a local mix of major components. Full article

(This article belongs to the Special Issue Experimental Study and Modeling of Biomass Pyrolysis)

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25 pages, 30911 KiB

Open AccessEditor’s ChoiceReview

Laser Powder Bed Fusion of Polymers: Quantitative Research Direction Indices

by Ihsan Murat Kusoglu, Carlos Doñate-Buendía, Stephan Barcikowski and Bilal Gökce

Materials 2021, 14(5), 1169; https://doi.org/10.3390/ma14051169 - 2 Mar 2021

Cited by 47 | Viewed by 5366

Abstract

Research on Laser Powder Bed Fusion (L-PBF) of polymer powder feedstocks has raised over the last decade due to the increased utilization of the fabricated parts in aerospace, automotive, electronics, and healthcare applications. A total of 600 Science Citation Indexed articles were published [...] Read more.

Research on Laser Powder Bed Fusion (L-PBF) of polymer powder feedstocks has raised over the last decade due to the increased utilization of the fabricated parts in aerospace, automotive, electronics, and healthcare applications. A total of 600 Science Citation Indexed articles were published on the topic of L-PBF of polymer powder feedstocks in the last decade, being cited more than 10,000 times leading to an h-index of 46. This study statistically evaluates the 100 most cited articles to extract reported material, process, and as-built part properties to analyze the research trends. PA12, PEEK, and TPU are the most employed polymer powder feedstocks, while size, flowability, and thermal behavior are the standardly reported material properties. Likewise, process properties such as laser power, scanning speed, hatch spacing, powder layer thickness, volumetric energy density, and areal energy density are extracted and evaluated. In addition, material and process properties of the as-built parts such as tensile test, flexural test, and volumetric porosity contents are analyzed. The incorporation of additives is found to be an effective route to enhance mechanical and functional properties. Carbon-based additives are typically employed in applications where mechanical properties are essential. Carbon fibers, Ca-phosphates, and SiO₂ are the most reported additives in the evaluated SCI-expanded articles for L-PBF of polymer powder feedstocks. A comprehensive data matrix is extracted from the evaluated SCI-index publications, and a principal component analysis (PCA) is performed to explore correlations between reported material, process, and as-built parts. Full article

(This article belongs to the Special Issue Specialty Polymers for Additive Manufacturing)

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11 pages, 1817 KiB

Open AccessEditor’s ChoiceArticle

Comparison of Transmission Measurement Methods of Elastic Waves in Phononic Band Gap Materials

by Maximilian Wormser, Daniel A. Kiefer, Stefan J. Rupitsch and Carolin Körner

Materials 2021, 14(5), 1133; https://doi.org/10.3390/ma14051133 - 28 Feb 2021

Cited by 4 | Viewed by 2912

Abstract

Periodic cellular structures can exhibit metamaterial properties, such as phononic band gaps. In order to detect these frequency bands of strong wave attenuation experimentally, several devices for wave excitation and measurement can be applied. In this work, piezoelectric transducers are utilized to excite [...] Read more.

Periodic cellular structures can exhibit metamaterial properties, such as phononic band gaps. In order to detect these frequency bands of strong wave attenuation experimentally, several devices for wave excitation and measurement can be applied. In this work, piezoelectric transducers are utilized to excite two additively manufactured three-dimensional cellular structures. For the measurement of the transmission factor, we compare two methods. First, the transmitted waves are measured with the same kind of piezoelectric transducer. Second, a laser Doppler vibrometer is employed to scan the mechanical vibrations of the sample on both the emitting and receiving surfaces. The additional comparison of two different methods of spatial averaging of the vibrometer data, that is, the quadratic mean and arithmetic mean, provides insight into the way the piezoelectric transducers convert the transmitted signal. Experimental results are supported by numerical simulations of the dispersion relation and a simplified transmission simulation. Full article

(This article belongs to the Special Issue Advances in Mechanical Metamaterials)

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13 pages, 2400 KiB

Open AccessEditor’s ChoiceArticle

Study of Radiation Characteristics of Intrinsic Josephson Junction Terahertz Emitters with Different Thickness of Bi₂Sr₂CaCu₂O_8+δ Crystals

by Takanari Kashiwagi, Takumi Yuasa, Genki Kuwano, Takashi Yamamoto, Manabu Tsujimoto, Hidetoshi Minami and Kazuo Kadowaki

Materials 2021, 14(5), 1135; https://doi.org/10.3390/ma14051135 - 28 Feb 2021

Cited by 8 | Viewed by 2868

Abstract

The radiation intensity from the intrinsic Josephson junction high-

T_{c}

superconductor Bi

_{2}

Sr

_{2}

CaCu

_{2}

O

_{8 + δ}

terahertz emitters (Bi2212-THz emitters) is one of the most important characteristics for application uses of the device. In principle, it would [...] Read more.

The radiation intensity from the intrinsic Josephson junction high-

T_{c}

superconductor Bi

_{2}

Sr

_{2}

CaCu

_{2}

O

_{8 + δ}

terahertz emitters (Bi2212-THz emitters) is one of the most important characteristics for application uses of the device. In principle, it would be expected to be improved with increasing the number of intrinsic Josephson junctions N in the emitters. In order to further improve the device characteristics, we have developed a stand alone type of mesa structures (SAMs) of Bi2212 crystals. Here, we understood the radiation characteristics of our SAMs more deeply, after we studied the radiation characteristics from three SAMs (S1, S2, and S3) with different thicknesses. Comparing radiation characteristics of the SAMs in which the number of intrinsic Josephson junctions are N∼ 1300 (S1), 2300 (S2), and 3100 (S3), respectively, the radiation intensity, frequency as well as the characteristics of the device working bath temperature are well understood. The strongest radiation of the order of few tens of microwatt was observed from the thickest SAM of S3. We discussed this feature through the

N^{2}

-relationship and the radiation efficiency of a patch antenna. The thinner SAM of S1 can generate higher radiation frequencies than the thicker one of S3 due to the difference of the applied voltage per junctions limited by the heat-removal performance of the device structures. The observed features in this study are worthwhile designing Bi2212-THz emitters with better emission characteristics for many applications. Full article

(This article belongs to the Special Issue Superconducting and Quantum Metamaterials, Metacircuits, and Metadevices)

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15 pages, 3882 KiB

Open AccessEditor’s ChoiceArticle

Evaluation of the Effects of Cement and Lime with Rice Husk Ash as an Additive on Strength Behavior of Coastal Soil

by Zahraalsadat Eliaslankaran, Nik Norsyahariati Nik Daud, Zainuddin Md. Yusoff and Vahid Rostami

Materials 2021, 14(5), 1140; https://doi.org/10.3390/ma14051140 - 28 Feb 2021

Cited by 28 | Viewed by 3662

Abstract

Coastal accretion and erosion are unavoidable processes as some coastal sediments undergo modification and stabilization. This study was conducted to investigate the geotechnical behavior of soil collected from Bagan Lalang coast and treated with lime, cement, and rice husk ash (RHA) to design [...] Read more.

Coastal accretion and erosion are unavoidable processes as some coastal sediments undergo modification and stabilization. This study was conducted to investigate the geotechnical behavior of soil collected from Bagan Lalang coast and treated with lime, cement, and rice husk ash (RHA) to design a low-cost alternative mixture with environmentally friendly characteristics. Laboratory tests were carried out to analyze the physical properties of the soil (Atterberg limits and compaction properties), together with mechanical characteristics (direct shear and unconfined compressive strength (UCS) tests) to determine the effect of different ratios of stabilizer/pozzolan on the coastal soil and the optimum conditions for each mixture. Part of the purpose of this study was also to analyze the shear behavior of the coastal soil and monitor the maximum axial compressive stress that the treated specimens can bear under zero confining pressure. Compared to the natural soil, the soil treated with lime and rice husk ash (LRHA) in the ratio of 1:2 (8% lime content) showed a tremendous increase in shear stress under the normal stress of 200 kPa. The strength parameters such as the cohesion (c) and internal friction angle (ϕ) values showed a significant increase. Cohesion values increased considerably in samples cured for 90 days compared to specimens cured for 7 days with additional LRHA in the ratio of 1:2 (28%). Full article

(This article belongs to the Special Issue Silica and Silica-based Materials for Biotechnology, Polymer Composites and Environmental Protection)

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14 pages, 13758 KiB

Open AccessEditor’s ChoiceArticle

Porosity Analysis of Additive Manufactured Parts Using CAQ Technology

by Peter Pokorný, Štefan Václav, Jana Petru and Michaela Kritikos

Materials 2021, 14(5), 1142; https://doi.org/10.3390/ma14051142 - 28 Feb 2021

Cited by 9 | Viewed by 2884

Abstract

Components produced by additive technology are implemented in various spheres of industry, such as automotive or aerospace. This manufacturing process can lead to making highly optimized parts. There is not enough information about the quality of the parts produced by additive technologies, especially [...] Read more.

Components produced by additive technology are implemented in various spheres of industry, such as automotive or aerospace. This manufacturing process can lead to making highly optimized parts. There is not enough information about the quality of the parts produced by additive technologies, especially those made from metal powder. The research in this article deals with the porosity of components produced by additive technologies. The components used for the research were manufactured by the selective laser melting (SLM) method. The shape of these components is the same as the shape used for the tensile test. The investigated parts were printed with orientation in two directions, Z and XZ with respect to the machine platform. The printing strategy was “stripe”. The material used for printing of the parts was SS 316L-0407. The printing parameters were laser power of 200 W, scanning speed of 650 mm/s, and the thickness of the layer was 50 µm. A non-destructive method was used for the components’ porosity evaluation. The scanning was performed by CT machine METROTOM 1500. The radiation parameters used for getting 3D scans were voltage 180 kV, current 900 µA, detector resolution 1024 × 1024 px, voxel size 119.43 µm, number of projections 1050, and integration time 2000 ms. This entire measurement process responds to the computer aided quality (CAQ) technology. VG studio MAX 3.0 software was used to evaluate the obtained data. The porosity of the parts with Z and XZ orientation was also evaluated for parts’ thicknesses of 1, 2, and 3 mm, respectively. It has been proven by this experimental investigation that the printing direction of the part in the additive manufacturing process under question affects its porosity. Full article

(This article belongs to the Special Issue The Science and Technology of 3D Printing)

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25 pages, 4815 KiB

Open AccessEditor’s ChoiceReview

Sustainable End-of-Life Management of Wind Turbine Blades: Overview of Current and Coming Solutions

by Leon Mishnaevsky

Materials 2021, 14(5), 1124; https://doi.org/10.3390/ma14051124 - 27 Feb 2021

Cited by 107 | Viewed by 18399

Abstract

Various scenarios of end-of-life management of wind turbine blades are reviewed. “Reactive” strategies, designed to deal with already available, ageing turbines, installed in the 2000s, are discussed, among them, maintenance and repair, reuse, refurbishment and recycling. The main results and challenges of “pro-active [...] Read more.

Various scenarios of end-of-life management of wind turbine blades are reviewed. “Reactive” strategies, designed to deal with already available, ageing turbines, installed in the 2000s, are discussed, among them, maintenance and repair, reuse, refurbishment and recycling. The main results and challenges of “pro-active strategies”, designed to ensure recyclability of new generations of wind turbines, are discussed. Among the main directions, the wind turbine blades with thermoplastic and recyclable thermoset composite matrices, as well as wood, bamboo and natural fiber-based composites were reviewed. It is argued that repair and reuse of wind turbine blades, and extension of the blade life has currently a number of advantages over other approaches. While new recyclable materials have been tested in laboratories, or in some cases on small or medium blades, there are remaining technological challenges for their utilization in large wind turbine blades. Full article

(This article belongs to the Special Issue Experimental and Numerical Analysis of Innovative Engineering Structures)

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24 pages, 12311 KiB

Open AccessEditor’s ChoiceArticle

Mesoscale Modelling of Concretes Subjected to Triaxial Loadings: Mechanical Properties and Fracture Behaviour

by Qingqing Chen, Yuhang Zhang, Tingting Zhao, Zhiyong Wang and Zhihua Wang

Materials 2021, 14(5), 1099; https://doi.org/10.3390/ma14051099 - 26 Feb 2021

Cited by 10 | Viewed by 2512

Abstract

The mechanical properties and fracture behaviour of concretes under different triaxial stress states were investigated based on a 3D mesoscale model. The quasistatic triaxial loadings, namely, compression–compression–compression (C–C–C), compression–tension–tension (C–T–T) and compression–compression–tension (C–C–T), were simulated using an implicit solver. The mesoscopic modelling with [...] Read more.

The mechanical properties and fracture behaviour of concretes under different triaxial stress states were investigated based on a 3D mesoscale model. The quasistatic triaxial loadings, namely, compression–compression–compression (C–C–C), compression–tension–tension (C–T–T) and compression–compression–tension (C–C–T), were simulated using an implicit solver. The mesoscopic modelling with good robustness gave reliable and detailed damage evolution processes under different triaxial stress states. The lateral tensile stress significantly influenced the multiaxial mechanical behaviour of the concretes, accelerating the concrete failure. With low lateral pressures or tensile stress, axial cleavage was the main failure mode of the specimens. Furthermore, the concretes presented shear failures under medium lateral pressures. The concretes experienced a transition from brittle fracture to plastic failure under high lateral pressures. The Ottosen parameters were modified by the gradient descent method and then the failure criterion of the concretes in the principal stress space was given. The failure criterion could describe the strength characteristics of concrete materials well by being fitted with experimental data under different triaxial stress states. Full article

(This article belongs to the Special Issue Concrete Technology and Mechanical Properties of Concretes)

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19 pages, 1126 KiB

Open AccessEditor’s ChoiceReview

Effect of UV Irradiation and TiO₂-Photocatalysis on Airborne Bacteria and Viruses: An Overview

by Nina Bono, Federica Ponti, Carlo Punta and Gabriele Candiani

Materials 2021, 14(5), 1075; https://doi.org/10.3390/ma14051075 - 25 Feb 2021

Cited by 110 | Viewed by 10903

Abstract

Current COVID-19 pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has put a spotlight on the spread of infectious diseases brought on by pathogenic airborne bacteria and viruses. In parallel with a relentless search for therapeutics and vaccines, considerable effort [...] Read more.

Current COVID-19 pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has put a spotlight on the spread of infectious diseases brought on by pathogenic airborne bacteria and viruses. In parallel with a relentless search for therapeutics and vaccines, considerable effort is being expended to develop ever more powerful technologies to restricting the spread of airborne microorganisms in indoor spaces through the minimization of health- and environment-related risks. In this context, UV-based and photocatalytic oxidation (PCO)-based technologies (i.e., the combined action of ultraviolet (UV) light and photocatalytic materials such as titanium dioxide (TiO₂)) represent the most widely utilized approaches at present because they are cost-effective and ecofriendly. The virucidal and bactericidal effect relies on the synergy between the inherent ability of UV light to directly inactivate viral particles and bacteria through nucleic acid and protein damages, and the production of oxidative radicals generated through the irradiation of the TiO₂ surface. In this literature survey, we draw attention to the most effective UV radiations and TiO₂-based PCO technologies available and their underlying mechanisms of action on both bacteria and viral particles. Since the fine tuning of different parameters, namely the UV wavelength, the photocatalyst composition, and the UV dose (viz, the product of UV light intensity and the irradiation time), is required for the inactivation of microorganisms, we wrap up this review coming up with the most effective combination of them. Now more than ever, UV- and TiO₂-based disinfection technologies may represent a valuable tool to mitigate the spread of airborne pathogens. Full article

(This article belongs to the Section Advanced Nanomaterials and Nanotechnology)

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14 pages, 1538 KiB

Open AccessEditor’s ChoiceArticle

Poly(Ethylene Furanoate) along Its Life-Cycle from a Polycondensation Approach to High-Performance Yarn and Its Recyclate

by Tim Höhnemann, Mark Steinmann, Stefan Schindler, Martin Hoss, Simon König, Antje Ota, Martin Dauner and Michael R. Buchmeiser

Materials 2021, 14(4), 1044; https://doi.org/10.3390/ma14041044 - 23 Feb 2021

Cited by 25 | Viewed by 5868

Abstract

We report on the pilot scale synthesis and melt spinning of poly(ethylene furanoate) (PEF), a promising bio-based fiber polymer that can heave mechanical properties in the range of commercial poly(ethylene terephthalate) (PET) fibers. Catalyst optimization and solid state polycondensation (SSP) allowed for intrinsic [...] Read more.

We report on the pilot scale synthesis and melt spinning of poly(ethylene furanoate) (PEF), a promising bio-based fiber polymer that can heave mechanical properties in the range of commercial poly(ethylene terephthalate) (PET) fibers. Catalyst optimization and solid state polycondensation (SSP) allowed for intrinsic viscosities of PEF of up to 0.85 dL·g⁻¹. Melt-spun multifilament yarns reached a tensile strength of up to 65 cN·tex⁻¹ with an elongation of 6% and a modulus of 1370 cN·tex⁻¹. The crystallization behavior of PEF was investigated by differential scanning calorimetry (DSC) and XRD after each process step, i.e., after polymerization, SSP, melt spinning, drawing, and recycling. After SSP, the previously amorphous polymer showed a crystallinity of 47%, which was in accordance with literature. The corresponding XRD diffractograms showed signals attributable to α-PEF. Additional, clearly assignable signals at 2θ > 30° are discussed. A completely amorphous structure was observed by XRD for as-spun yarns, while a crystalline phase was detected on drawn yarns; however, it was less pronounced than for the granules and independent of the winding speed. Full article

(This article belongs to the Special Issue Novel Synthetic Fibers for Textile Applications)

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19 pages, 4660 KiB

Open AccessEditor’s ChoiceArticle

The Role of Solvents in Lithography-Based Ceramic Manufacturing of Lithium Disilicate

by Malte Hartmann, Markus Pfaffinger and Jürgen Stampfl

Materials 2021, 14(4), 1045; https://doi.org/10.3390/ma14041045 - 23 Feb 2021

Cited by 12 | Viewed by 3285

Abstract

Digital dentistry is increasingly replacing conventional methods of manually producing dental restorations. With regards to computer-aided manufacturing (CAM), milling is state of the art. Additive manufacturing (AM), as a complementary approach, has also found its way into dental practices and laboratories. Vat photo-polymerization [...] Read more.

Digital dentistry is increasingly replacing conventional methods of manually producing dental restorations. With regards to computer-aided manufacturing (CAM), milling is state of the art. Additive manufacturing (AM), as a complementary approach, has also found its way into dental practices and laboratories. Vat photo-polymerization is gaining increasing attention, because it enables the production of full ceramic restorations with high precision. One of the two predominantly used ceramic materials for these applications is lithium disilicate, Li₂Si₂O₅. This glass ceramic exhibits a substantial fracture toughness, although possesses much lower bending strength, than the other predominantly used ceramic material, zirconia. Additionally, it shows a much more natural optical appearance, due to its inherent translucency, and therefore is considered for anterior tooth restorations. In this work, an optimized formulation for photo-reactive lithium disilicate suspensions, to be processed by vat photo-polymerization, is presented. Following the fundamental theoretical considerations regarding this processing technique, a variety of solvents was used to adjust the main properties of the suspension. It is shown that this solvent approach is a useful tool to effectively optimize a suspension with regards to refractive index, rheology, and debinding behavior. Additionally, by examining the effect of the absorber, the exposure time could be reduced by a factor of ten. Full article

(This article belongs to the Special Issue 3D-Printed Dental Materials)

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14 pages, 21007 KiB

Open AccessEditor’s ChoiceArticle

Temperature-Dependent Photoluminescence of ZnO Thin Films Grown on Off-Axis SiC Substrates by APMOCVD

by Ivan Shtepliuk, Volodymyr Khranovskyy, Arsenii Ievtushenko and Rositsa Yakimova

Materials 2021, 14(4), 1035; https://doi.org/10.3390/ma14041035 - 22 Feb 2021

Cited by 5 | Viewed by 2974

Abstract

The growth of high-quality ZnO layers with optical properties congruent to those of bulk ZnO is still a great challenge. Here, for the first time, we systematically study the morphology and optical properties of ZnO layers grown on SiC substrates with off-cut angles [...] Read more.

The growth of high-quality ZnO layers with optical properties congruent to those of bulk ZnO is still a great challenge. Here, for the first time, we systematically study the morphology and optical properties of ZnO layers grown on SiC substrates with off-cut angles ranging from 0° to 8° by using the atmospheric pressure meta–organic chemical vapor deposition (APMOCVD) technique. Morphology analysis revealed that the formation of the ZnO films on vicinal surfaces with small off-axis angles (1.4°–3.5°) follows the mixed growth mode: from one side, ZnO nucleation still occurs on wide (0001) terraces, but from another side, step-flow growth becomes more apparent with the off-cut angle increasing. We show for the first time that the off-cut angle of 8° provides conditions for step-flow growth of ZnO, resulting in highly improved growth morphology, respectively structural quality. Temperature-dependent photoluminescence (PL) measurements showed a strong dependence of the excitonic emission on the off-cut angle. The dependences of peak parameters for bound exciton and free exciton emissions on temperature were analyzed. The present results provide a correlation between the structural and optical properties of ZnO on vicinal surfaces and can be utilized for controllable ZnO heteroepitaxy on SiC toward device-quality ZnO epitaxial layers with potential applications in nano-optoelectronics. Full article

(This article belongs to the Special Issue Progress in Optical Characterization of Semiconductor Nanomaterials and Devices)

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