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Materials, Volume 13, Issue 9 (May-1 2020) – 202 articles

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Cover Story (view full-size image) Despite their many advantages, dye-sensitized solar cells (DSSC) still need some improvements to [...] Read more.
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Open AccessArticle
Single-Crown, Short and Ultra-Short Implants, in Association with Simultaneous Internal Sinus Lift in the Atrophic Posterior Maxilla: A Three-Year Retrospective Study
Materials 2020, 13(9), 2208; https://doi.org/10.3390/ma13092208 - 11 May 2020
Viewed by 350
Abstract
As the atrophic posterior maxilla often presents serious limitations for dental implant procedures, a minimally invasive technique was proposed. The study aimed to retrospectively evaluate the outcomes of short and ultra-short locking-taper implants, placed in combination with a modified osteotome sinus floor elevation [...] Read more.
As the atrophic posterior maxilla often presents serious limitations for dental implant procedures, a minimally invasive technique was proposed. The study aimed to retrospectively evaluate the outcomes of short and ultra-short locking-taper implants, placed in combination with a modified osteotome sinus floor elevation procedure (internal sinus lift technique) in the posterior maxilla. A total of 31 patients received 51 locking-taper implants. Clinical and radiographic examinations were performed before treatment, at loading time, and after three years. Seven implants of 8.0 mm, 23 implants of 6.0 mm, and 21 implants 5.0 mm in length were rehabilitated with single-crown restorations. Implant survival at three-year follow-up was 96.08%. Pre-operative residual crestal bone height of 5.2 (1.41) (median (interquartile range)) mm increased to 7.59 (1.97) mm at the 36-month follow-up, with an average intra-sinus bone height gain of 3.17 ± 1.13 (mean ± standard deviation) mm. Mean peri-implant crestal bone loss was 0.29 (0.46) mm and mean first bone-to-implant contact point shifted apically to 0.12 (0.34) mm. It can be suggested with confidence that implants used in the study, placed in conjunction with an internal sinus floor elevation technique, can be restored with single crowns as a predictable treatment for the edentulous regions of the posterior maxilla. Full article
(This article belongs to the Section Biomaterials)
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Open AccessReview
Metal Oxide Compact Electron Transport Layer Modification for Efficient and Stable Perovskite Solar Cells
Materials 2020, 13(9), 2207; https://doi.org/10.3390/ma13092207 - 11 May 2020
Viewed by 641
Abstract
Perovskite solar cells (PSCs) have appeared as a promising design for next-generation thin-film photovoltaics because of their cost-efficient fabrication processes and excellent optoelectronic properties. However, PSCs containing a metal oxide compact layer (CL) suffer from poor long-term stability and performance. The quality of [...] Read more.
Perovskite solar cells (PSCs) have appeared as a promising design for next-generation thin-film photovoltaics because of their cost-efficient fabrication processes and excellent optoelectronic properties. However, PSCs containing a metal oxide compact layer (CL) suffer from poor long-term stability and performance. The quality of the underlying substrate strongly influences the growth of the perovskite layer. In turn, the perovskite film quality directly affects the efficiency and stability of the resultant PSCs. Thus, substrate modification with metal oxide CLs to produce highly efficient and stable PSCs has drawn attention. In this review, metal oxide-based electron transport layers (ETLs) used in PSCs and their systemic modification are reviewed. The roles of ETLs in the design and fabrication of efficient and stable PSCs are also discussed. This review will guide the further development of perovskite films with larger grains, higher crystallinity, and more homogeneous morphology, which correlate to higher stable PSC performance. The challenges and future research directions for PSCs containing compact ETLs are also described with the goal of improving their sustainability to reach new heights of clean energy production. Full article
(This article belongs to the Special Issue Organic Solar Cell and Optoelectronic Functional Materials)
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Open AccessArticle
Optical Etching to Pattern Microstructures on Plastics by Vacuum Ultraviolet Light
Materials 2020, 13(9), 2206; https://doi.org/10.3390/ma13092206 - 11 May 2020
Viewed by 313
Abstract
We proposed and demonstrated an optical dry etching method for transferring a pattern on a photomask to a surface of plastics by decomposing the irradiated area using the high energy of vacuum ultraviolet light (VUV) at room temperature and pressure. Two kinds of [...] Read more.
We proposed and demonstrated an optical dry etching method for transferring a pattern on a photomask to a surface of plastics by decomposing the irradiated area using the high energy of vacuum ultraviolet light (VUV) at room temperature and pressure. Two kinds of wavelengths of 160 nm and 172 nm were used as the vacuum ultraviolet light, and the patterning performances for polymethyl methacrylate (PMMA) and polycarbonate (PC) were compared. As a result, it was revealed that proportional relationships were obtained between the etching rate and the irradiation dose for both wavelengths, and the cross-sectional profiles were anisotropic. In addition, both PMMA and PC were etched at a wavelength of 160 nm, whereas PC could not be etched at a wavelength of 172 nm, suggesting that it correlates with the bond dissociation energies of the molecular bonds of the materials and the energies of the photons. Furthermore, by combining this method with the optical bonding method that we had previously developed to bond surfaces irradiated with VUV, we have demonstrated a method for fabricating microfluidic devices by irradiating only with VUV. This paper shows that this technique is a new microfabrication method suitable for simple and mass production of plastic materials. Full article
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Open AccessArticle
Influence of a Coaxial Electrospraying System on the n-Hexadecane/Polycaprolactone Phase Change Microcapsules Properties
Materials 2020, 13(9), 2205; https://doi.org/10.3390/ma13092205 - 11 May 2020
Viewed by 296
Abstract
Electrospraying is considered to be a green, high-efficiency method for synthesizing phase change microcapsules (mPCMs) for possible applications in the fields of energy storage and thermal regulation. In this study, a coaxial nozzle was used to prepare n-hexadecane/polycaprolactone (PCL) microparticles. The objectives of [...] Read more.
Electrospraying is considered to be a green, high-efficiency method for synthesizing phase change microcapsules (mPCMs) for possible applications in the fields of energy storage and thermal regulation. In this study, a coaxial nozzle was used to prepare n-hexadecane/polycaprolactone (PCL) microparticles. The objectives of this study were to investigate the influence of working parameters and solutions on morphology, particle size, thermal properties and encapsulation efficiency. Thus, three theoretical loading contents in n-hexadecane (30%, 50% and 70% w/w) and two concentrations of PCL (5 and 10% w/v) were used. The structures, morphologies and thermal properties of mPCMs were characterized by optical microscopy (OM), scanning electron microscopy (SEM), differential scanning calorimeter (DSC), and thermogravimetric analysis (TGA). Spherical microcapsules with a mean diameter of 10–20 µm were prepared. The increased concentration of n-hexadecane and PCL resulted in a change in the particle size distribution from a poly-disperse to monodisperse size distribution and in a change in the surface state from porous to non-porous. In addition, higher encapsulation efficiency (96%) and loading content (67%) were achieved by the coaxial nozzle using the high core-shell ratio (70/30) and 10% w/v of PCL. The latent heat of the mPCMs reached about 134 J.g−1. In addition, it was also observed that the thermal stability was improved by using a coaxial system rather than a single nozzle. Full article
(This article belongs to the Special Issue Phase Change Materials: Characterizations for Uses)
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Open AccessArticle
Investigations on Mechanical Properties of Lattice Structures with Different Values of Relative Density Made from 316L by Selective Laser Melting (SLM)
Materials 2020, 13(9), 2204; https://doi.org/10.3390/ma13092204 - 11 May 2020
Viewed by 294
Abstract
Nine variants of regular lattice structures with different relative densities have been designed and successfully manufactured. The produced structures have been subjected to geometrical quality control, and the manufacturability of the implemented selective laser melting (SLM) technique has been assessed. It was found [...] Read more.
Nine variants of regular lattice structures with different relative densities have been designed and successfully manufactured. The produced structures have been subjected to geometrical quality control, and the manufacturability of the implemented selective laser melting (SLM) technique has been assessed. It was found that the dimensions of the produced lattice struts differ from those of the designed struts. These deviations depend on the strut orientation in relation to the specimen-building direction. Additionally, the microstructures and phase compositions of the obtained structures were characterized and compared with those of conventionally produced 316L stainless steel. The microstructure analysis and X-ray diffraction (XRD) patterns revealed a single austenite phase in the SLM samples. Both a certain broadening and a displacement of the austenite peaks were observed due to residual stresses and a crystallographic texture induced by the SLM process. Furthermore, the mechanical behavior of the lattice structure material has been defined. It was demonstrated that under both quasi-static and dynamic testing, lattice structures with high relative densities are stretch-dominated, whereas those with low relative densities are bending-dominated. Moreover, the linear dependency between the value of energy absorption and relative density under dynamic loading conditions has been established. Full article
(This article belongs to the Special Issue Mechanical Behavior of Composite Materials)
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Open AccessArticle
Influence of SiC Sludge on the Microstructure of Geopolymers
Materials 2020, 13(9), 2203; https://doi.org/10.3390/ma13092203 - 11 May 2020
Viewed by 272
Abstract
There are considerable resource reuse and environmental concerns regarding SiC sludge (SiCS) that results from cutting silicon ingots into wafers. In the current study, the effect of the Na2SiO3 solution/sodium hydroxide solution (NS/SS) mass ratio and SiCS amount on metakaolin [...] Read more.
There are considerable resource reuse and environmental concerns regarding SiC sludge (SiCS) that results from cutting silicon ingots into wafers. In the current study, the effect of the Na2SiO3 solution/sodium hydroxide solution (NS/SS) mass ratio and SiCS amount on metakaolin geopolymers was found during geopolymerization system performance. The results indicate that while NS/SS ratio was relatively low, increasing the NaOH content resulted in a sufficient amount of OH in the system to increase the solubility and hinder polycondensation, as indicated by the bulk density and setting-time results; since the polycondensation was inhibited, the mechanical strength was reduced. This study demonstrated that a geopolymer can be formed from a substitution of 10% SiCS and with an NS/SS ratio of 1.6, and that this geopolymer is a feasible material. Full article
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Open AccessArticle
An Investigation of the Work Hardening Behavior in Interrupted Cutting Inconel 718 under Cryogenic Conditions
Materials 2020, 13(9), 2202; https://doi.org/10.3390/ma13092202 - 11 May 2020
Viewed by 267
Abstract
The severe work hardening phenomenon generated in the machining of Inconel 718 is harmful to continue cutting processes, while being good for the component’s service performance. This paper investigates the performance of cryogenic assisted machining used in the cutting processes, which can reduce [...] Read more.
The severe work hardening phenomenon generated in the machining of Inconel 718 is harmful to continue cutting processes, while being good for the component’s service performance. This paper investigates the performance of cryogenic assisted machining used in the cutting processes, which can reduce the waste of fluids. The influence of dry and cryogenic machining conditions with different cutting speeds on the work hardening layer is investigated based on the interrupted cutting of Inconel 718. Cutting temperature distribution obtained from simulations under different conditions is used to discuss the potential mechanism of work hardening. Then, the depth of work hardening and degree of work hardening (DWH) are investigated to analyze the surface deformation behavior, which strengthens the machined surface during metal cutting processes. From the cutting experiments, the depth of the work hardening layer can reach more than 60 μm under the given cutting conditions. In addition, a deeper zone can be obtained by the cooling of liquid nitrogen, which may potentially enhance the wear performance of the component. The results obtained from this work can be utilized to effectively control the work hardening layer beneath the surface, which can be applied to improve the service performance. Full article
(This article belongs to the Special Issue Advanced Design for Manufacturing Processes)
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Open AccessArticle
Phase Stability of Nanocrystalline Grains of Rare-Earth Oxides (Sm2O3 and Eu2O3) Confined in Magnesia (MgO) Matrix
Materials 2020, 13(9), 2201; https://doi.org/10.3390/ma13092201 - 11 May 2020
Viewed by 266
Abstract
Rare-earth (RE) oxides are important in myriad fields, including metallurgy, catalysis, and ceramics. However, the phase diagram of RE oxides in the nanoscale might differ from the phase diagrams for bulk, thus attracting attention nowadays. We suggest that grain size in the nanoscale [...] Read more.
Rare-earth (RE) oxides are important in myriad fields, including metallurgy, catalysis, and ceramics. However, the phase diagram of RE oxides in the nanoscale might differ from the phase diagrams for bulk, thus attracting attention nowadays. We suggest that grain size in the nanoscale also determines the obtained crystallographic phase along with temperature and pressure. For this purpose, nanoparticles of Sm2O3 and Eu2O3 were mixed in an inert MgO matrix via the sol-gel method. This preparation method allowed better isolation of the oxide particles, thus hindering the grain growth process associated with increasing the temperature. The mixed oxides were compared to pure oxides, which were heat-treated using two methods: gradual heating versus direct heating to the phase transition temperature. The cubic phase in pure oxides was preserved to a higher extent in the gradual heating treatment compared to the direct heating treatment. Additionally, in MgO, even a higher extent of the cubic phase was preserved at higher temperatures compared to the pure oxide, which transformed into the monoclinic phase at the same temperature in accordance with the phase diagram for bulk. This indicates that the cubic phase is the equilibrium phase for nanosized particles and is determined also by size. Full article
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Open AccessFeature PaperArticle
(Bio)Degradable Polymeric Materials for Sustainable Future—Part 3: Degradation Studies of the PHA/Wood Flour-Based Composites and Preliminary Tests of Antimicrobial Activity
Materials 2020, 13(9), 2200; https://doi.org/10.3390/ma13092200 - 11 May 2020
Viewed by 423
Abstract
The need for a cost reduction of the materials derived from (bio)degradable polymers forces research development into the formation of biocomposites with cheaper fillers. As additives can be made using the post-consumer wood, generated during wood products processing, re-use of recycled waste materials [...] Read more.
The need for a cost reduction of the materials derived from (bio)degradable polymers forces research development into the formation of biocomposites with cheaper fillers. As additives can be made using the post-consumer wood, generated during wood products processing, re-use of recycled waste materials in the production of biocomposites can be an environmentally friendly way to minimalize and/or utilize the amount of the solid waste. Also, bioactive materials, which possess small amounts of antimicrobial additives belong to a very attractive packaging industry solution. This paper presents a study into the biodegradation, under laboratory composting conditions, of the composites that consist of poly[(R)-3-hydroxybutyrate-co-4-hydroxybutyrate)] and wood flour as a polymer matrix and natural filler, respectively. Thermogravimetric analysis, differential scanning calorimetry and scanning electron microscopy were used to evaluate the degradation progress of the obtained composites with different amounts of wood flour. The degradation products were characterized by multistage electrospray ionization mass spectrometry. Also, preliminary tests of the antimicrobial activity of selected materials with the addition of nisin were performed. The obtained results suggest that the different amount of filler has a significant influence on the degradation profile. Full article
(This article belongs to the Special Issue Applications of Novel Biodegradable Polymeric Materials)
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Open AccessArticle
Manufacturing of Large Size and Highly Transparent Nd:YAG Ceramics by Pressure Slip-Casting and Post-Sintering by HIP: An Experimental and Simulation Study
Materials 2020, 13(9), 2199; https://doi.org/10.3390/ma13092199 - 11 May 2020
Viewed by 265
Abstract
This study reports the fabrication of Nd:YAG (i.e., Neodymium-doped Yttrium Aluminum Garnet: Y3-xNdxAl5O12) transparent ceramics of a large size by the pressure slip-casting forming technique. Colloidal suspensions of primary oxides (i.e., Y2O3 [...] Read more.
This study reports the fabrication of Nd:YAG (i.e., Neodymium-doped Yttrium Aluminum Garnet: Y3-xNdxAl5O12) transparent ceramics of a large size by the pressure slip-casting forming technique. Colloidal suspensions of primary oxides (i.e., Y2O3, Al2O3, Nd2O3, and SiO2 used as sintering aid) were cast under pressure through a porous membrane. Cakes with a good microstructural homogeneity and mean pore diameter of 90 nm were obtained. Modeling of the pressure slip-casting process at the millimetric to centimetric scale based on a computational fluid dynamics simulation showed good agreement with experimental results in terms of the casting kinetics (i.e., cake thickness and fluid flow as a function of time) and cake permeability. As a result, it was possible to better manage pressure casting parameters in order to obtain large size and homogeneous green parts. Finally, transparent Nd:YAG ceramics sintered by vacuum sintering, followed by post-sintering treatment by Hot Isostatic Pressing (HIP), demonstrated laser slope efficiency (51.7%) and optical-to-optical efficiency (44%) with 130 mJ of output laser energy at 1064 nm equivalent to commercial single crystals. Full article
(This article belongs to the Special Issue Production and Processing of High Performance Ceramic)
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Open AccessArticle
Effect of Jet Impingement Velocity and Angle on CO2 Erosion–Corrosion with and without Sand for API 5L-X65 Carbon Steel
Materials 2020, 13(9), 2198; https://doi.org/10.3390/ma13092198 - 11 May 2020
Viewed by 248
Abstract
Most oil and gas production wells have plenty of corrosive species present along with solid particles. In such production environments, CO2 gas can dissolve in free phase water and form carbonic acid (H2CO3). This carbonic acid, along with [...] Read more.
Most oil and gas production wells have plenty of corrosive species present along with solid particles. In such production environments, CO2 gas can dissolve in free phase water and form carbonic acid (H2CO3). This carbonic acid, along with fluid flow and with/without solid particles (sand or other entrained particles), can result in unpredictable severe localized CO2 corrosion and/or erosion–corrosion (EC). So, in this work, the CO2 EC performance of API 5L X-65 carbon steel, a commonly used material in many oil and gas piping infrastructure, was investigated. A recirculating flow loop was used to perform these studies at three different CO2 concentrations (pH values of 4.5, 5.0, and 5.5), two impingement velocities (8 and 16 m/s), three impingement angles (15°, 45°, and 90°), and with/without 2000 ppm sand particles for a duration of 3 h in 0.2 M NaCl solution at room temperature. Corrosion products were characterized using FE-SEM, EDS, and XRD. The CO2 EC rates were found to decrease with an increase in the pH value due to the increased availability of H+ ions. The highest CO2 erosion–corrosion rates were observed at a 45° impingement angle in the presence of solid particles under all conditions. It was also observed that a change in pH value influenced the morphology and corrosion resistance of the corrosion scales. Full article
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Open AccessCommunication
Study on the Directional Solidification Process of an Aluminum Alloy Bar in Multishell Mold Being Gradually Immersed in Water
Materials 2020, 13(9), 2197; https://doi.org/10.3390/ma13092197 - 11 May 2020
Viewed by 246
Abstract
A multishell mold structure and water-immersion cooling method (MSMWI) is proposed for the directional solidification of castings. A four-layer-shell sand mold was designed for a bar with diameter of 40 mm. As the aluminum melt was poured, the multishell mold was gradually immersed [...] Read more.
A multishell mold structure and water-immersion cooling method (MSMWI) is proposed for the directional solidification of castings. A four-layer-shell sand mold was designed for a bar with diameter of 40 mm. As the aluminum melt was poured, the multishell mold was gradually immersed in water, and the water level drove the advancement of the solidification front from bottom to top. The multishell mold was helpful for the heat insulation of its upper part, and its bottom was chilled by the water. Therefore, directional solidification of the bar was vertically realized. The water-cooled solidification process of the bar was 5.8 times faster than that by air natural cooling (MSMNC), and the temperature gradient was increased by 78 times. The secondary dendrite arm spacing (SDAS) and eutectic silicon were significantly refined. Its tensile strength, elongation, and hardness were increased by 56%, 185%, and 62.6%, respectively. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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Open AccessArticle
CeO2:Mn3O4 Catalytic Micro-Converters Tuned for CH4 Detection Based on Catalytic Combustion under Real Operating Conditions
Materials 2020, 13(9), 2196; https://doi.org/10.3390/ma13092196 - 11 May 2020
Viewed by 285
Abstract
Mesoporous CeO2:Mn3O4 materials (3:7 and 7:3 molar ratio) were prepared by co-precipitation and deposited as porous thick films over alumina (Al2O3) planar substrate provided with Pt meander. The aim was oriented towards detecting low [...] Read more.
Mesoporous CeO2:Mn3O4 materials (3:7 and 7:3 molar ratio) were prepared by co-precipitation and deposited as porous thick films over alumina (Al2O3) planar substrate provided with Pt meander. The aim was oriented towards detecting low levels methane (CH4) at moderate operating temperatures. Herein we demonstrated that the sensitivity of catalytic micro-converters (CMCs) towards a given peak of CH4 concentration corresponds to specific gas-surface interaction phenomena. More precisely, a transition from thermal conductivity to combustion rate is likely to occur when CMCs are operated under real atmospheric conditions (normal pressure, presence of relative humidity, and constant operating temperature). The response to CH4 was analyzed over different gas flows and different gas concentrations under the same operating regime. The materials were fully characterized by adsorption-desorption isotherms, H2-Temperature Programmed Reduction (H2-TPR), X-ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscopy (SEM), and Raman spectroscopies. Thus, the applicative aspect of using CeO2:Mn3O4 as moderate temperature CMC for CH4 detection is brought to the fore. Full article
(This article belongs to the Special Issue Advanced Materials for Gas Sensors)
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Open AccessArticle
Impact of an Antiresonant Oxide Island on the Lasing of Lateral Modes in VCSELs
Materials 2020, 13(9), 2195; https://doi.org/10.3390/ma13092195 - 11 May 2020
Viewed by 323
Abstract
Use of antiresonant structures is a proven, efficient method of improving lateral mode selectivity in VCSELs. In this paper, we analyze the impact of a low-refractive antiresonant oxide island buried in a top VCSEL mirror on the lasing conditions of lateral modes of [...] Read more.
Use of antiresonant structures is a proven, efficient method of improving lateral mode selectivity in VCSELs. In this paper, we analyze the impact of a low-refractive antiresonant oxide island buried in a top VCSEL mirror on the lasing conditions of lateral modes of different orders. By performing comprehensive thermal, electrical, and optical numerical analysis of the VCSEL device, we show the impact of the size and location of the oxide island on the current-crowding effect and compute threshold currents for various lateral modes. If the island is placed close to the cavity, the threshold shows strong oscillations, which for moderate island distances can be tuned to increase the side mode discrimination. We are therefore able to pinpoint the most important factors influencing mode discrimination and to identify oxide island parameters capable of providing single-lateral-mode emission. Full article
(This article belongs to the Special Issue Photonic Materials and Devices)
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Open AccessArticle
Influences of Low Intensity on Diode Parameters of CdTe Solar Cells
Materials 2020, 13(9), 2194; https://doi.org/10.3390/ma13092194 - 10 May 2020
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Abstract
This study deals with the CdS/CdTe solar cells under low illumination intensity, with cell #1 for the shunt resistance exceeding 100,000 Ω·cm2 and cell #2 for the shunt resistance above 1000 Ω·cm2. The diode parameter variations with the decline of [...] Read more.
This study deals with the CdS/CdTe solar cells under low illumination intensity, with cell #1 for the shunt resistance exceeding 100,000 Ω·cm2 and cell #2 for the shunt resistance above 1000 Ω·cm2. The diode parameter variations with the decline of the irradiance intensity are illustrated by dividing 0–100 mW/cm−2 into a number of small intensity ranges for J–V measurements and assuming the diode parameters to be constant within each range, the diode parameters of each range including the series resistance, the shunt resistance, the reverse saturation current density and the ideality factor are then extracted by employing an analytical approach. The mechanism of the cell performance deviations are also investigated by basic theories, reports and experiments. For cell #1 with higher Rsh corresponding to less traps, Rsh shows a upward tendency as the irradiance declines, n and J0 exhibit a rise with the irradiance and keep nearly unchanged at the low irradiance values mainly due to recombination and carrier contributions, Rs shows a slight increase when the irradiance intensity goes down because of the resistance of CdTe absorption layer. For cell #2 with lower Rsh corresponding to more traps, with the decrease of the illumination intensity, Rsh increases sharply only for captured carrier reduction, Rs goes steadily up similarly, n and J0 exhibit a decline with the irradiance due to recombination shift. It should be pointed out that Rs varies much smoother than the traditional approximation of a reciprocal of differential at short circuit, and the distribution of Rsh is diverse, and an average Rsh of for each intensity range can reflect the variation trend. Full article
(This article belongs to the Special Issue Materials for Solar Photovoltaic Applications)
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Open AccessFeature PaperArticle
The Multidirectional Auxeticity and Negative Linear Compressibility of a 3D Mechanical Metamaterial
Materials 2020, 13(9), 2193; https://doi.org/10.3390/ma13092193 - 10 May 2020
Viewed by 391
Abstract
In this work, through the use of a theoretical model, we analyse the potential of a specific three-dimensional mechanical metamaterial composed of arrowhead-like structural units to exhibit a negative Poisson’s ratio for an arbitrary loading direction. Said analysis allows us to assess its [...] Read more.
In this work, through the use of a theoretical model, we analyse the potential of a specific three-dimensional mechanical metamaterial composed of arrowhead-like structural units to exhibit a negative Poisson’s ratio for an arbitrary loading direction. Said analysis allows us to assess its suitability for use in applications where materials must be able to respond in a desired manner to a stimulus applied in multiple directions. As a result of our studies, we show that the analysed system is capable of exhibiting auxetic behaviour for a broad range of loading directions, with isotropic behaviour being shown in some planes. In addition to that, we show that there are also certain loading directions in which the system manifests negative linear compressibility. This enhances its versatility and suitability for a number of applications where materials exhibiting auxetic behaviour or negative linear compressibility are normally implemented. Full article
(This article belongs to the Special Issue Advances in Mechanical Metamaterials)
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Open AccessArticle
In Situ and Ex Situ Characterization of the Microstructure Formation in Ni-Cr-Si Alloys during Rapid Solidification—Toward Alloy Design for Laser Additive Manufacturing
Materials 2020, 13(9), 2192; https://doi.org/10.3390/ma13092192 - 10 May 2020
Viewed by 429
Abstract
Laser beam-based deposition methods such as laser cladding or additive manufacturing of metals promises improved properties, performance, and reliability of the materials and therefore rely heavily on understanding the relationship between chemical composition, rapid solidification processing conditions, and resulting microstructural features. In this [...] Read more.
Laser beam-based deposition methods such as laser cladding or additive manufacturing of metals promises improved properties, performance, and reliability of the materials and therefore rely heavily on understanding the relationship between chemical composition, rapid solidification processing conditions, and resulting microstructural features. In this work, the phase formation of four Ni-Cr-Si alloys was studied as a function of cooling rate and chemical composition using a liquid droplet rapid solidification technique. Post mortem x-ray diffraction, scanning electron microscopy, and in situ synchrotron microbeam X-ray diffraction shows the present and evolution of the rapidly solidified microstructures. Furthermore, the obtained results were compared to standard laser deposition tests. In situ microbeam diffraction revealed that due to rapid cooling and an increasing amount of Cr and Si, metastable high-temperature silicides remain in the final microstructure. Due to more sluggish interface kinetics of intermetallic compounds than that of disorder solid solution, an anomalous eutectic structure becomes dominant over the regular lamellar microstructure at high cooling rates. The rapid solidification experiments produced a microstructure similar to the one generated in laser coating thus confirming that this rapid solidification test allows a rapid pre-screening of alloys suitable for laser beam-based processing techniques. Full article
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Open AccessArticle
Modeling and Design of SHPB to Characterize Brittle Materials under Compression for High Strain Rates
Materials 2020, 13(9), 2191; https://doi.org/10.3390/ma13092191 - 10 May 2020
Viewed by 370
Abstract
This paper presents an analytical prediction coupled with numerical simulations of a split Hopkinson pressure bar (SHPB) that could be used during further experiments to measure the dynamic compression strength of concrete. The current study combines experimental, modeling and numerical results, permitting an [...] Read more.
This paper presents an analytical prediction coupled with numerical simulations of a split Hopkinson pressure bar (SHPB) that could be used during further experiments to measure the dynamic compression strength of concrete. The current study combines experimental, modeling and numerical results, permitting an inverse method by which to validate measurements. An analytical prediction is conducted to determine the waves propagation present in SHPB using a one-dimensional theory and assuming a strain rate dependence of the material strength. This method can be used by designers of new SPHB experimental setups to predict compressive strength or strain rates reached during tests, or to check the consistencies of predicted results. Numerical simulation results obtained using LS-DYNA finite element software are also presented in this paper, and are used to compare the predictions with the analytical results. This work focuses on an SPHB setup that can accurately identify the strain rate sensitivities of concrete or brittle materials. Full article
(This article belongs to the Special Issue High Performance Concrete)
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Open AccessArticle
A 4 Year Human, Randomized, Radiographic Study of Scalloped versus Non-Scalloped Cemented Implants
Materials 2020, 13(9), 2190; https://doi.org/10.3390/ma13092190 - 10 May 2020
Viewed by 331
Abstract
Marginal bone loss (MBL) is a key factor in long-term implant success rate. Among the different factors that influence MBL, it is the different implant shoulder designs, such as scalloped or non-scalloped, which have been widely studied on screw retained but not on [...] Read more.
Marginal bone loss (MBL) is a key factor in long-term implant success rate. Among the different factors that influence MBL, it is the different implant shoulder designs, such as scalloped or non-scalloped, which have been widely studied on screw retained but not on cemented retained implants. Thus, the aim of the present study was to evaluate the MBL around scalloped and non-scalloped cemented retained dental implants after 4 years of loading, in humans. A total of 15 patients were enrolled in the present study. A radiographic and clinical examination was performed after implant placement (T0) and after 4 years from it (T1). The results demonstrated a differential MBL (T1-T0) of 2.436 ± 1.103 mm and 1.923 ± 1.021 mm, respectively for test (scalloped) and control (non-scalloped) groups with a statistically significant difference between them. On the other hand, no statistically significant differences were found between the groups in terms of prosthetic complication and abutment decementation, whilst ceramic crowns chipping was shown in both groups. In conclusion, the use of a scalloped platform did not provide better results on the maintenance of MBL after 4 years follow-up. In this study, this probably was determined by multiple factors, among which was the subcrestal insertion of scalloped implants. Full article
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Open AccessArticle
Comparative Surface Morphology, Chemical Composition, and Cytocompatibility of Bio-C Repair, Biodentine, and ProRoot MTA on hDPCs
Materials 2020, 13(9), 2189; https://doi.org/10.3390/ma13092189 - 10 May 2020
Viewed by 534
Abstract
Biocompatibility is an essential property for any vital pulp material that may interact with the dental pulp tissues. Accordingly, this study aimed to compare the chemical composition and ultrastructural morphology of Biodentine (Septodont, Saint Maur-des-Fosses, France), ProRoot MTA (Dentsply Tulsa Dental Specialties, Johnson [...] Read more.
Biocompatibility is an essential property for any vital pulp material that may interact with the dental pulp tissues. Accordingly, this study aimed to compare the chemical composition and ultrastructural morphology of Biodentine (Septodont, Saint Maur-des-Fosses, France), ProRoot MTA (Dentsply Tulsa Dental Specialties, Johnson City, TN, USA), and Bio-C Repair (Angelus, Londrina, PR, Brazil), as well as their biological effects on human dental pulp cells. Chemical element characterization of the materials was undertaken using scanning electron microscopy and energy dispersive X-ray analysis (SEM-EDX). The cytotoxicity was assessed by analyzing the cell viability (MTT assay), cell morphology (immunofluorescence assay), and cell attachment (flow cytometry assay). The results were statistically analyzed using ANOVA and Tukey’s test (p < 0.05). EDX revealed that ProRoot MTA and Biodentine were mostly composed of calcium, carbon, and oxygen (among others), whereas Bio-C Repair evidenced a low concentration of calcium and the highest concentration of zirconium. SEM showed adequate attachment of human dental pulp cells (hDPCS) to vital pulp materials and cytoskeletal alterations were not observed in the presence of material eluates. Remarkably, the undiluted Biodentine group showed higher viability than the control group cells (without eluates) at 24 h, 48 h, and 72 h (p < 0.001). Based on the evidence derived from an in vitro cellular study, it was concluded that Bio-C Repair showed excellent cytocompatibility that was similar to Biodentine and ProRoot MTA. Full article
(This article belongs to the Special Issue Current and Future Trends in Dental Materials)
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Open AccessArticle
On the Chip Shaping and Surface Topography When Finish Cutting 17-4 PH Precipitation-Hardening Stainless Steel under Near-Dry Cutting Conditions
Materials 2020, 13(9), 2188; https://doi.org/10.3390/ma13092188 - 09 May 2020
Viewed by 369
Abstract
This study describes the surface topography of the 17-4 PH stainless steel machined under dry, wet and near-dry cutting conditions. Cutting speeds of 150–500 m/min, feeds of 0.05–0.4 mm/rev and 0.5 mm depth of cutting were applied. The research was based on the [...] Read more.
This study describes the surface topography of the 17-4 PH stainless steel machined under dry, wet and near-dry cutting conditions. Cutting speeds of 150–500 m/min, feeds of 0.05–0.4 mm/rev and 0.5 mm depth of cutting were applied. The research was based on the ‘parameter space investigation’ method. Surface roughness parameters, contour maps and material participation curves were analysed using the optical Sensofar S Neox 3D profilometer and the effect of feed, cutting speed and their mutual interaction was noticed. Changes in chip shape depending on the processing conditions are shown. Compared to dry machining, a reduction of Sa, Sq and Sz parameters of 38–48% was achieved for near-dry condition. For lower feeds and average cutting speeds valleys and ridges were observed on the surface machined under dry, wet and near-dry conditions. For higher feeds and middle and higher cutting speeds, deep valleys and high ridges were observed on the surface. Depending on the processing conditions, different textures of the machined surface were registered, particularly anisotropic mixed, periodic and periodically determined. In the Sa range of 0.4–0.8 μm for dry and wet conditions the surface isotropy is ~20%, under near-dry conditions it is ~60%. Full article
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Open AccessArticle
Obtaining a Wire of Biocompatible Superelastic Alloy Ti–28Nb–5Zr
Materials 2020, 13(9), 2187; https://doi.org/10.3390/ma13092187 - 09 May 2020
Viewed by 307
Abstract
Using the methods of electric arc melting, intermediate heat treatments, and consecutive intensive plastic deformation, a Ti–Nb–Zr alloy wire with a diameter of 1200 μm was obtained with a homogeneous chemical and phase (β-Ti body-centered crystal lattice) composition corresponding to the presence of [...] Read more.
Using the methods of electric arc melting, intermediate heat treatments, and consecutive intensive plastic deformation, a Ti–Nb–Zr alloy wire with a diameter of 1200 μm was obtained with a homogeneous chemical and phase (β-Ti body-centered crystal lattice) composition corresponding to the presence of superelasticity and shape memory effect, corrosion resistance and biocompatibility. Perhaps the wire structure is represented by grains with a nanoscale diameter. For the wire obtained after stabilizing annealing, the proof strength Rp0.2 is 635 MPa, tensile strength is 840 MPa and Young’s modulus is 22 GPa, relative elongation is 6.76%. No toxicity was detected. The resulting wire is considered to be promising for medical use. Full article
(This article belongs to the Special Issue Shape Memory Materials: New Design Concepts and Novel Materials)
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Open AccessArticle
Microstructure and Degradation of Mortar Containing Waste Glass Aggregate as Evaluated by Various Microscopic Techniques
Materials 2020, 13(9), 2186; https://doi.org/10.3390/ma13092186 - 09 May 2020
Viewed by 348
Abstract
The primary aim of this article is to focus on the alkali-silica reaction (ASR) in mortar specimens containing coloured waste glass used as an aggregate. Mortar expansion was measured using the ASTM C 1260 accelerated test procedure until the specimens disintegrated. Special attention [...] Read more.
The primary aim of this article is to focus on the alkali-silica reaction (ASR) in mortar specimens containing coloured waste glass used as an aggregate. Mortar expansion was measured using the ASTM C 1260 accelerated test procedure until the specimens disintegrated. Special attention was paid to the microscopic examination of the damaged mortar. Various methods were used for this purpose, including optical microscopy in reflected and transmitted light with one and two crossed polarizers. The specimens were also subjected to the scanning electron microscopy observations with energy dispersive spectroscopy (SEM-EDS). The data obtained from these techniques provided information on the mechanism of glass-containing mortar degradation due to ASR and also allowed the comparison of different microscopic techniques in terms of the information they can provide on ASR occurrence. Full article
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Open AccessReview
DNA Origami as Emerging Technology for the Engineering of Fluorescent and Plasmonic-Based Biosensors
Materials 2020, 13(9), 2185; https://doi.org/10.3390/ma13092185 - 09 May 2020
Viewed by 457
Abstract
DNA nanotechnology is a powerful and promising tool for the development of nanoscale devices for numerous and diverse applications. One of the greatest potential fields of application for DNA nanotechnology is in biomedicine, in particular biosensing. Thanks to the control over their size, [...] Read more.
DNA nanotechnology is a powerful and promising tool for the development of nanoscale devices for numerous and diverse applications. One of the greatest potential fields of application for DNA nanotechnology is in biomedicine, in particular biosensing. Thanks to the control over their size, shape, and fabrication, DNA origami represents a unique opportunity to assemble dynamic and complex devices with precise and predictable structural characteristics. Combined with the addressability and flexibility of the chemistry for DNA functionalization, DNA origami allows the precise design of sensors capable of detecting a large range of different targets, encompassing RNA, DNA, proteins, small molecules, or changes in physico-chemical parameters, that could serve as diagnostic tools. Here, we review some recent, salient developments in DNA origami-based sensors centered on optical detection methods (readout) with a special emphasis on the sensitivity, the selectivity, and response time. We also discuss challenges that still need to be addressed before this approach can be translated into robust diagnostic devices for bio-medical applications. Full article
(This article belongs to the Special Issue Advances in Bio-Inspired Materials for Medical Applications)
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Open AccessArticle
Machinability Analysis and Optimization in Wire EDM of Medical Grade NiTiNOL Memory Alloy
Materials 2020, 13(9), 2184; https://doi.org/10.3390/ma13092184 - 09 May 2020
Viewed by 437
Abstract
NiTiNOL (Nickel–Titanium) shape memory alloys (SMAs) are ideal replacements for titanium alloys used in bio-medical applications because of their superior properties like shape memory and super elasticity. The machining of NiTiNOL alloy is challenging, as it is a difficult to cut material. Hence, [...] Read more.
NiTiNOL (Nickel–Titanium) shape memory alloys (SMAs) are ideal replacements for titanium alloys used in bio-medical applications because of their superior properties like shape memory and super elasticity. The machining of NiTiNOL alloy is challenging, as it is a difficult to cut material. Hence, in the current research the experimental studies on machinability aspects of medical grade NiTiNOL SMA during wire electric discharge machining (WEDM) using zinc coated brass wire as electrode material have been carried out. Pulse time (Ton), pause time (Toff), wire feed (WF), and servo voltage (SV) are chosen as varying input process variables and the effects of their combinational values on output responses such as surface roughness (SR), material removal rate (MRR), and tool wear rate (TWR) are studied through response surface methodology (RSM) based developed models. Modified differential evolution (MDE) optimization technique has been developed and the convergence curve of the same has been compared with the results of differential evolution (DE) technique. Scanning electron microscopy (SEM) and energy dispersive X-ray spectrography (EDS) analysis are carried out to study the surface morphology of the machined alloy. SV is found to be more influential process parameter for achieving better MRR with minimal SR and TWR, followed by Ton, Toff, and WF. The WF has good impact on reduced SR and TWR responses and found to be least significant in maximizing MRR. Full article
(This article belongs to the Special Issue Machinability of Metallic Materials and Composites)
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Open AccessArticle
Bond Strength Tests under Pure Shear and Tension between Masonry and Sprayed Mortar
Materials 2020, 13(9), 2183; https://doi.org/10.3390/ma13092183 - 09 May 2020
Viewed by 247
Abstract
Sprayed mortar or shotcrete is a construction technology that could enhance existing masonry buildings’ resilience by reinforcing low-safety load-bearing walls. Many factors affect the resistance of shotcrete-reinforced structures. One of the most important is the bond strength at the interface between the shotcrete [...] Read more.
Sprayed mortar or shotcrete is a construction technology that could enhance existing masonry buildings’ resilience by reinforcing low-safety load-bearing walls. Many factors affect the resistance of shotcrete-reinforced structures. One of the most important is the bond strength at the interface between the shotcrete and the reinforced wall. According to previous technical literature, bond strength usually has two evaluation criteria: shear and tensile strength. The experimental campaign described in this article focused on the bond strength between sprayed mortar and three masonry materials without the influence of normal force or constraint, as well as the roughness of these materials. The analysis of these tests focused on determining the relation between bond strength, roughness, and material strength. The analyses revealed that material strength has a more significant effect on bond strength than roughness, and bond strength is related to shrinkage of the materials. On the basis of previous theories, these researchers found that when there is no obvious influence due to normal force and constraint, the shear strength and tensile strength are different, and the shear strength is likely to be the cohesion force of the two materials. Finally, this article concludes with a novel logarithmic relationship between these strengths. Full article
(This article belongs to the Section Construction and Building Materials)
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Open AccessArticle
Fatigue Reliability Analysis of a Compressor Disk Based on Probability Cumulative Damage Criterion
Materials 2020, 13(9), 2182; https://doi.org/10.3390/ma13092182 - 09 May 2020
Viewed by 262
Abstract
The reliability of aero engine has a direct impact on the flight safety of the whole plane. With the continuous improvement of performance requirements of aero engines, the related fatigue and reliability problems also appear. For the fatigue failure characteristics of the typical [...] Read more.
The reliability of aero engine has a direct impact on the flight safety of the whole plane. With the continuous improvement of performance requirements of aero engines, the related fatigue and reliability problems also appear. For the fatigue failure characteristics of the typical component (compressor disk) in an aero engine, the fatigue reliability of its multi-site damage structure in service is analyzed by using probability cumulative damage criterion in this paper. The probability distribution definitions of life, damage and damage threshold are discussed and the relationship among them is also introduced by the new proposed criterion. Meanwhile, a method to determine the probability distribution of cumulative damage threshold and probability life prediction is carried out, based on which a hierarchical index system of statistical analysis and reliability modeling principle on the system level is further constructed for compressor disk. At the end of the paper, a certain cruise of fighter plane is analyzed to verify the validity of the new model. Emphasizing the difference between the compressor disk and traditional component, the new reliability analysis model developed in this study is basically reasonable for most of the load histories for the compressor disk, other than the traditional one, especially for the changeable and complex cruise missions. Full article
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Open AccessArticle
Direct Exposure of Dry Enzymes to Atmospheric Pressure Non-Equilibrium Plasmas: The Case of Tyrosinase
Materials 2020, 13(9), 2181; https://doi.org/10.3390/ma13092181 - 09 May 2020
Viewed by 292
Abstract
The direct interaction of atmospheric pressure non-equilibrium plasmas with tyrosinase (Tyr) was investigated under typical conditions used in surface processing. Specifically, Tyr dry deposits were exposed to dielectric barrier discharges (DBDs) fed with helium, helium/oxygen, and helium/ethylene mixtures, and effects on enzyme functionality [...] Read more.
The direct interaction of atmospheric pressure non-equilibrium plasmas with tyrosinase (Tyr) was investigated under typical conditions used in surface processing. Specifically, Tyr dry deposits were exposed to dielectric barrier discharges (DBDs) fed with helium, helium/oxygen, and helium/ethylene mixtures, and effects on enzyme functionality were evaluated. First of all, results show that DBDs have a measurable impact on Tyr only when experiments were carried out using very low enzyme amounts. An appreciable decrease in Tyr activity was observed upon exposure to oxygen-containing DBD. Nevertheless, the combined use of X-ray photoelectron spectroscopy and white-light vertical scanning interferometry revealed that, in this reactive environment, Tyr deposits displayed remarkable etching resistance, reasonably conferred by plasma-induced changes in their surface chemical composition as well as by their coffee-ring structure. Ethylene-containing DBDs were used to coat tyrosinase with a hydrocarbon polymer film, in order to obtain its immobilization. In particular, it was found that Tyr activity can be fully retained by properly adjusting thin film deposition conditions. All these findings enlighten a high stability of dry enzymes in various plasma environments and open new opportunities for the use of atmospheric pressure non-equilibrium plasmas in enzyme immobilization strategies. Full article
(This article belongs to the Special Issue Atmospheric Pressure Plasmas in Material Science)
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Open AccessArticle
In Situ Characterization of Damage Development in Cottonid Due to Quasi-Static Tensile Loading
Materials 2020, 13(9), 2180; https://doi.org/10.3390/ma13092180 - 09 May 2020
Viewed by 248
Abstract
Cottonid is a layered material based 100% on cellulose that holds excellent material properties by being completely sustainable. The finite nature of petroleum-based resources nowadays makes these properties significant for technical applications again. To understand how Cottonid reacts to application-oriented mechanical loads and [...] Read more.
Cottonid is a layered material based 100% on cellulose that holds excellent material properties by being completely sustainable. The finite nature of petroleum-based resources nowadays makes these properties significant for technical applications again. To understand how Cottonid reacts to application-oriented mechanical loads and how it fails, development of microstructural damage on the surface and in the volume of Cottonid was studied using innovative in situ testing techniques for the first time. Quasi-static tensile tests were comparatively performed in a scanning electron microscope as well as a microfocus computer tomograph, and the development of defects present in the initial condition of the material was investigated. In the elastic region, no visible damage initiation on the surface and a decrease of overall void volume within the gauge length could be detected. When reaching the yield strength, crack initiation on the surface starts at critical areas, like pores and microcracks, which propagation and assembly could be visualized via scanning electron micrographs. In the plastic region, an increase in void volume could be shown in the gauge length until final failure of the specimen. Innovative material testing techniques presented in this study support lifetime estimation in technical applications and understanding of process–structure–property relations. Particularly, characterization of microstructural damage development due to a mechanical load, which leads to final failure of the specimen, is essential to be able to create material models for lifetime prediction in respect to variable manufacturing or application parameters. Full article
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Open AccessArticle
Utilization of Composts for Adsorption of Methylene Blue from Aqueous Solutions: Kinetics and Equilibrium Studies
Materials 2020, 13(9), 2179; https://doi.org/10.3390/ma13092179 - 09 May 2020
Viewed by 249
Abstract
Utilization of composts as low-cost adsorbents is an important application in the field of environmental remediation, but these materials have not yet been extensively used for dye removal. In this work, we have studied the characteristics of adsorption of methylene blue onto two [...] Read more.
Utilization of composts as low-cost adsorbents is an important application in the field of environmental remediation, but these materials have not yet been extensively used for dye removal. In this work, we have studied the characteristics of adsorption of methylene blue onto two composts (a municipal solid waste compost and a pine bark compost). Kinetics and equilibrium batch experiments testing the influence of adsorbent particle size, solution pH and ionic strength were performed. Both composts have a high adsorption capacity for methylene blue, similar to other low-cost adsorbents. Kinetics of adsorption followed a pseudo-first-order model, with maximum adsorption reached after a contact time of two hours. Equilibrium adsorption followed a Langmuir model in general. Reduction of particle size only increased adsorption slightly for composted pine bark. Increase in ionic strength had no effect on adsorption by municipal solid waste compost, but increased adsorption by composted pine bark. Modification of pH between 5 and 7 did not influence adsorption in any case. Overall, the results suggest that electrostatic interaction between the cationic dye and the anionic functional groups in the composts is not the only mechanism involved in adsorption. In conclusion, the use of composts for dye removal is a likely application, in particular for those composts presenting limitations for agricultural use. Full article
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