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Materials, Volume 12, Issue 8 (April-2 2019)

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Cover Story (view full-size image) In our search to discover interesting photophysical materials, we have stumbled upon two [...] Read more.
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Open AccessArticle
Pronounced Impact of p-Type Carriers and Reduction of Bandgap in Semiconducting ZnTe Thin Films by Cu Doping for Intermediate Buffer Layer in Heterojunction Solar Cells
Materials 2019, 12(8), 1359; https://doi.org/10.3390/ma12081359
Received: 11 February 2019 / Revised: 16 April 2019 / Accepted: 18 April 2019 / Published: 25 April 2019
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Abstract
Stabilized un-doped Zinc Telluride (ZnTe) thin films were grown on glass substrates under vacuum using a closed space sublimation (CSS) technique. A dilute copper nitrate solution (0.1/100 mL) was prepared for copper doping, known as an ion exchange process, in the matrix of [...] Read more.
Stabilized un-doped Zinc Telluride (ZnTe) thin films were grown on glass substrates under vacuum using a closed space sublimation (CSS) technique. A dilute copper nitrate solution (0.1/100 mL) was prepared for copper doping, known as an ion exchange process, in the matrix of the ZnTe thin film. The reproducible polycrystalline cubic structure of undoped and the Cu doped ZnTe thin films with preferred orientation (111) was confirmed by X-rays diffraction (XRD) technique. Lattice parameter analyses verified the expansion of unit cell volume after incorporation of Cu species into ZnTe thin films samples. The micrographs of scanning electron microscopy (SEM) were used to measure the variation in crystal sizes of samples. The energy dispersive X-rays were used to validate the elemental composition of undoped and Cu-doped ZnTe thin films. The bandgap energy 2.24 eV of the ZnTe thin film decreased after doping Cu to 2.20 eV and may be due to the introduction of acceptors states near to valance band. Optical studies showed that refractive index was measured from 2.18 to 3.24, whereas thicknesses varied between 220 nm to 320 nm for un-doped and Cu doped ZnTe thin film, respectively, using the Swanepoel model. The oxidation states of Zn+2, Te+2, and Cu+1 through high resolution X-ray photoelectron spectroscopy (XPS) analyses was observed. The resistivity of thin films changed from ~107 Ω·cm or undoped ZnTe to ~1 Ω·cm for Cu-doped ZnTe thin film, whereas p-type carrier concentration increased from 4 × 109 cm−2 to 1.4 × 1011 cm−2, respectively. These results predicted that Cu-doped ZnTe thin film can be used as an ideal, efficient, and stable intermediate layer between metallic and absorber back contact for the heterojunction thin film solar cell technology. Full article
(This article belongs to the Special Issue Interface Engineering in Organic/Inorganic Hybrid Solar Cells)
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Open AccessArticle
Diffusive Steel Scrap Melting in Carbon-Saturated Hot Metal—Phenomenological Investigation at the Solid–Liquid Interface
Materials 2019, 12(8), 1358; https://doi.org/10.3390/ma12081358
Received: 5 April 2019 / Revised: 22 April 2019 / Accepted: 23 April 2019 / Published: 25 April 2019
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Abstract
The oxygen steelmaking process in a Linz-Donawitz (LD) converter is responsible for more than 70% of annual crude steel production. Optimization of the process control and numerical simulation of the LD converter are some of the current challenges in ferrous metallurgical research. Because [...] Read more.
The oxygen steelmaking process in a Linz-Donawitz (LD) converter is responsible for more than 70% of annual crude steel production. Optimization of the process control and numerical simulation of the LD converter are some of the current challenges in ferrous metallurgical research. Because of the process conditions and oxidation of impurities of the hot metal, a lot of chemical heat is generated. Therefore, steel scrap is charged as a coolant with the economical side aspect of its recycling. One of the more complex aspects is, among others, the dissolution and melting behaviour of the scrap in carbon-saturated hot metal. Heat and mass transfer act simultaneously, which has already been investigated by several researchers using different experimental approaches. The appearances at the interface between solid steel and liquid hot metal during diffusive scrap melting have been described theoretically but never investigated in detail. After an experimental investigation under natural and forced convective conditions, the samples were further investigated with optical microscopy and electron probe microanalysis (EPMA). A steep carbon concentration gradient in the liquid appeared, which started at an interface carbon concentration equal to the concentration on the solid side of the interface. Moreover, the boundary layer thickness moved towards zero, which symbolized that the boundary layer theory based on thermodynamic equilibrium was not valid. This fact was concluded through the prevailing dynamic conditions formed by natural and forced convection. Full article
(This article belongs to the Special Issue Grain Boundary Segregation and Related Phenomena in Metals and Alloys)
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Open AccessFeature PaperCommunication
Multifunctional Operation of an Organic Device with Three-Dimensional Architecture
Materials 2019, 12(8), 1357; https://doi.org/10.3390/ma12081357
Received: 12 March 2019 / Revised: 4 April 2019 / Accepted: 22 April 2019 / Published: 25 April 2019
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Abstract
This work aims to show the feasibility of an innovative approach for the manufacturing of organic-based devices with a true three-dimensional and customizable structure that is made possible by plastic templates, fabricated by additive manufacturing methods, and coated by conducting organic thin films. [...] Read more.
This work aims to show the feasibility of an innovative approach for the manufacturing of organic-based devices with a true three-dimensional and customizable structure that is made possible by plastic templates, fabricated by additive manufacturing methods, and coated by conducting organic thin films. Specifically, a three-dimensional prototype based on a polyamide structure covered by poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) using the dip-coating technique demonstrated a multifunctional character. The prototype is indeed able to operate both as a three-terminal device showing the typical response of organic electrochemical transistors (OECTs), with a higher amplification performance with respect to planar (2D) all-PEDOT:PSS OECTs, and as a two-terminal device able to efficiently implement a resistive sensing of water vaporization and perspiration, showing performances at least comparable to that of state-of-art resistive humidity sensors based on pristine PEDOT:PSS. To our knowledge, this is the first reported proof-of-concept of a true 3D structured OECT, obtained by exploiting a Selective laser sintering approach that, though simple in terms of 3D layout, paves the way for the integration of sensors based on OECTs into three-dimensional objects in various application areas. Full article
(This article belongs to the Special Issue Organic-Semiconductor-Based Devices)
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Open AccessArticle
Synthesis of the Tetragonal Phase of Zintl’s NaTl and Its Structure Determination from Powder Diffraction Data
Materials 2019, 12(8), 1356; https://doi.org/10.3390/ma12081356
Received: 14 March 2019 / Revised: 4 April 2019 / Accepted: 11 April 2019 / Published: 25 April 2019
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Abstract
A tetragonal distortion of the long-time known NaTl structure at 298 K was observed in different experimental setups, including Zintl’s original procedure of reducing Tl(I)-iodide by sodium liquid ammonia solutions. The powder diffraction pattern obtained by the high temperature synthesis using classical solid-state [...] Read more.
A tetragonal distortion of the long-time known NaTl structure at 298 K was observed in different experimental setups, including Zintl’s original procedure of reducing Tl(I)-iodide by sodium liquid ammonia solutions. The powder diffraction pattern obtained by the high temperature synthesis using classical solid-state techniques allowed a model-independent unambiguous structure solution and refinement of tetragonal distorted NaTl (Rp = 0.0179, wRp = 0.0246, R = 0.0477, wR = 0.0527, GooF = 1.24). Full article
(This article belongs to the Special Issue Advances in Zintl Phases)
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Open AccessArticle
Effect of Alloying Elements on the α-γ Phase Transformation in Iron
Materials 2019, 12(8), 1355; https://doi.org/10.3390/ma12081355
Received: 8 April 2019 / Revised: 17 April 2019 / Accepted: 22 April 2019 / Published: 25 April 2019
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Abstract
Small concentrations of alloying elements can modify the α-γ phase transition temperature Tc of Fe. We study this effect using an atomistic model based on a set of many-body interaction potentials for iron and several alloying elements. Free-energy calculations based [...] Read more.
Small concentrations of alloying elements can modify the α - γ phase transition temperature T c of Fe. We study this effect using an atomistic model based on a set of many-body interaction potentials for iron and several alloying elements. Free-energy calculations based on perturbation theory allow us to determine the change in T c introduced by the alloying element. The resulting changes are in semi-quantitative agreement with experiment. The effect is traced back to the shape of the pair potential describing the interaction between the Fe and the alloying atom. Full article
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Open AccessArticle
Thermal and Mechanical Interfacial Behaviors of Graphene Oxide-Reinforced Epoxy Composites Cured by Thermal Latent Catalyst
Materials 2019, 12(8), 1354; https://doi.org/10.3390/ma12081354
Received: 1 April 2019 / Revised: 17 April 2019 / Accepted: 24 April 2019 / Published: 25 April 2019
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Abstract
A series of composites was prepared from a diglycidyl ether of bisphenol A (DGEBA) with different graphene filler contents to improve their mechanical performance and thermal stability. Graphene oxide (GO) and GO modified with hexamethylene tetraamine (HMTA) were selected as reinforcing agents. As [...] Read more.
A series of composites was prepared from a diglycidyl ether of bisphenol A (DGEBA) with different graphene filler contents to improve their mechanical performance and thermal stability. Graphene oxide (GO) and GO modified with hexamethylene tetraamine (HMTA) were selected as reinforcing agents. As a latent cationic initiator and curing agent, N-benzylepyrizinium hexafluoroantimonate (N-BPH) was used. The effect of fillers and their contents on the mechanical properties and thermal stability of the composites were studied. Fracture toughness improved by 23% and 40%, and fracture energy was enhanced by 1.94- and 2.27-fold, for the composites containing 0.04 wt.% GO and HMTA-GO, respectively. The gradual increase in fracture toughness at higher filler contents was attributed to both crack deflection and pinning mechanisms. Maximum thermal stability in the composites was achieved by using up to 0.1 wt.% graphene fillers. Full article
(This article belongs to the Special Issue Graphene Oxide: Synthesis, Reduction, and Frontier Applications)
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Open AccessArticle
4D Printing Self-Morphing Structures
Materials 2019, 12(8), 1353; https://doi.org/10.3390/ma12081353
Received: 29 March 2019 / Revised: 20 April 2019 / Accepted: 22 April 2019 / Published: 25 April 2019
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Abstract
The main objective of this paper is to introduce complex structures with self-bending/morphing/rolling features fabricated by 4D printing technology, and replicate their thermo-mechanical behaviors using a simple computational tool. Fused deposition modeling (FDM) is implemented to fabricate adaptive composite structures with performance-driven functionality [...] Read more.
The main objective of this paper is to introduce complex structures with self-bending/morphing/rolling features fabricated by 4D printing technology, and replicate their thermo-mechanical behaviors using a simple computational tool. Fused deposition modeling (FDM) is implemented to fabricate adaptive composite structures with performance-driven functionality built directly into materials. Structural primitives with self-bending 1D-to-2D features are first developed by functionally graded 4D printing. They are then employed as actuation elements to design complex structures that show 2D-to-3D shape-shifting by self-bending/morphing. The effects of printing speed on the self-bending/morphing characteristics are investigated in detail. Thermo-mechanical behaviors of the 4D-printed structures are simulated by introducing a straightforward method into the commercial finite element (FE) software package of Abaqus that is much simpler than writing a user-defined material subroutine or an in-house FE code. The high accuracy of the proposed method is verified by a comparison study with experiments and numerical results obtained from an in-house FE solution. Finally, the developed digital tool is implemented to engineer several practical self-morphing/rolling structures. Full article
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Open AccessArticle
Multi-Objective Optimization for Grinding Parameters of 20CrMnTiH Gear with Ceramic Microcrystalline Corundum
Materials 2019, 12(8), 1352; https://doi.org/10.3390/ma12081352
Received: 23 March 2019 / Revised: 16 April 2019 / Accepted: 24 April 2019 / Published: 25 April 2019
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Abstract
(1) The alloy material 20CrMnTiH is widely used in gear manufacturing, but difficult to process, and its quantity (efficiency) and quality (surface quality) are generally negative correlation indicators. As a difficult but realistic problem, it is of important practical significance to explore how [...] Read more.
(1) The alloy material 20CrMnTiH is widely used in gear manufacturing, but difficult to process, and its quantity (efficiency) and quality (surface quality) are generally negative correlation indicators. As a difficult but realistic problem, it is of important practical significance to explore how to efficiently grind high-precision low-carbon alloy gear workpieces. (2) Firstly, the pixel method was applied to analyze the grinding principles and explore the grinding parameters—the grinding wheel speed and grinding wheel frame moving speed—as well as the feed rate, which impacts the grinding indicators. Secondly, based on the ceramic microcrystalline corundum grinding wheel and the 20CrMnTiH gear workpiece, controlled experiments with 28 groups of grinding parameters were conducted. Moreover, the impact curves of the grinding parameters on the grinding indicators—the grinding efficiency, grinding wheel life, and surface roughness—were obtained by the multiple linear regression method. Finally, the multi-objective optimization method was used to comprehensively optimize the grinding process. (3) Compared with the traditional grinding process, under optimized grinding parameters, the 20CrMnTiH gear workpieces have a lower surface roughness and a longer grinding wheel life, and require a shorter time to achieve grinding accuracy. (4) The grinding experiments showed that the grinding parameters are linearly related to the grinding indicators. The optimization results show that the precision, efficiency, and economy of the 20CrMnTiH gear grinding process have been improved via the comprehensive optimization of the grinding parameters. Full article
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Open AccessArticle
Microstructure and Mechanical Properties of 34CrMo4 Steel for Gas Cylinders Formed by Hot Drawing and Flow Forming
Materials 2019, 12(8), 1351; https://doi.org/10.3390/ma12081351
Received: 19 March 2019 / Revised: 14 April 2019 / Accepted: 23 April 2019 / Published: 25 April 2019
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Abstract
An integral manufacturing process with hot drawing and cold flow forming was proposed for large-diameter seamless steel gas cylinders. The main purpose of this study was to find out the effects of the manufacturing process on the microstructure and mechanical properties of gas [...] Read more.
An integral manufacturing process with hot drawing and cold flow forming was proposed for large-diameter seamless steel gas cylinders. The main purpose of this study was to find out the effects of the manufacturing process on the microstructure and mechanical properties of gas cylinders made of 34CrMo4 steel. Two preformed cylinders were produced by hot drawing. One cylinder was then further manufactured by cold flow forming. The experiments were carried out using three types of material sample, namely, base material (BM), hot drawing cylinder (HD), and cold flow-formed cylinder (CF). Tensile and impact tests were performed to examine the mechanical properties of the cylinders in longitudinal and transverse directions. Microstructure evolution was analyzed by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) to reveal the relation between the mechanical properties and the microstructure of the material. It is found that the mechanical properties of the 34CrMo4 steel gas cylinders were significantly improved after hot drawing and flow forming plus a designed heat treatment, compared with the base material. The observations of microstructure features such as grain size, subgrain boundaries, and residual strain support the increase in mechanical properties due to the proposed manufacturing process. Full article
(This article belongs to the Special Issue Advanced Metal Forming Processes)
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Open AccessArticle
In Vitro Effect of Drilling Speed on the Primary Stability of Narrow Diameter Implants with Varying Thread Designs Placed in Different Qualities of Simulated Bone
Materials 2019, 12(8), 1350; https://doi.org/10.3390/ma12081350
Received: 24 March 2019 / Revised: 16 April 2019 / Accepted: 19 April 2019 / Published: 25 April 2019
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Abstract
It is hypothesized that there is no statistically significant impact of drilling speed (DS) on the primary stability (PS) of narrow-diameter implants (NDIs) with varying thread designs placed in dense and soft simulated bone. The aim of this in vitro study was to [...] Read more.
It is hypothesized that there is no statistically significant impact of drilling speed (DS) on the primary stability (PS) of narrow-diameter implants (NDIs) with varying thread designs placed in dense and soft simulated bone. The aim of this in vitro study was to evaluate the impact of DS on the PS of NDIs with varying thread designs placed in dense and soft simulated bone. Two hundred and forty osteotomies for placement of various implant macro-designs were divided into three groups (80 implants per group): Group A (NobelActive, 3.0/11.5 mm); Group B (Astra OsseoSpeed-EV, 3.0/11 mm); and Group C (Eztetic-Zimmer, 3.1/11.5 mm) implants. These implants were placed in artificial dense and soft simulated bone using DSs of 800 and 2000 revolutions per minute (RPM). Resonance frequency analysis (RFA) and implant stability quotient (ISQ) were assessed. Group comparisons were performed using the one-way analysis of variance with Tukey’s post hoc tests. Level of significance was set at P < 0.05. In groups A and B, there was no difference in the ISQ for NDIs inserted in dense bone at 800 and 2000 RPM. In Group C, ISQ was significantly higher for NDIs placed in dense bone at 800 PRM compared to 2000 RPM (P < 0.05). In Group A, ISQ values were significantly higher for NDIs inserted in soft bone at 2000 RPM as compared to those inserted at 800 RPM (P < 0.05). For NDIs, a lower drilling speed in dense artificial simulated bone and a higher drilling speed in soft artificial simulated bone is associated with high primary stability. Full article
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Open AccessArticle
New Organic/Inorganic Pigments Based on Azo Dye and Aluminum-Magnesium Hydroxycarbonates with Various Mg/Al Ratios
Materials 2019, 12(8), 1349; https://doi.org/10.3390/ma12081349
Received: 28 March 2019 / Revised: 18 April 2019 / Accepted: 23 April 2019 / Published: 25 April 2019
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Abstract
This study set out to investigate the impact of aluminum-magnesium hydroxycarbonates (LHs) with various Mg/Al ratios on the formation of hybrid pigments. The colorants were also evaluated for their flame-retardant properties. In the first part of the study, the hybrid pigments were submitted [...] Read more.
This study set out to investigate the impact of aluminum-magnesium hydroxycarbonates (LHs) with various Mg/Al ratios on the formation of hybrid pigments. The colorants were also evaluated for their flame-retardant properties. In the first part of the study, the hybrid pigments were submitted to comprehensive characterization using time-of-flight secondary ion mass spectrometry (TOF-SIMS), 27Al solid-state nuclear magnetic resonance (NMR) spectroscopy, powder X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA), and N2 adsorption as well as scanning and transmission electron microscopy (SEM/STEM). The relationship between the Mg/Al ratios of the LH carriers and the formation of lake pigments was explored. The TOF-SIMS spectrum of LH modified with azo chromophore (AC) showed an intense peak for the C19H15O5N2Mg+ ion, confirming metal-dye interactions. Incorporation of the organic colorant into the LH host enhanced its resistance to dissolution in organic solvent (butyl acetate), as well as improving its color stability under elevated temperatures. The second part of the study evaluated the flammability of ethylene-norbornene (EN) composites, in which the pigments had been applied as colorants. Cone calorimetry revealed that addition of the organic-inorganic pigments resulted in a substantial improvement of the flame retardancy, reflected by the decreased values of the heat release rate (HRRMAX) and total heat release parameter (THR) of the EN composites in comparison to a neat sample (unfilled EN). Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessArticle
Defect Chemistry and Na-Ion Diffusion in Na3Fe2(PO4)3 Cathode Material
Materials 2019, 12(8), 1348; https://doi.org/10.3390/ma12081348
Received: 22 March 2019 / Revised: 22 April 2019 / Accepted: 24 April 2019 / Published: 25 April 2019
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Abstract
In this work, we employ computational modeling techniques to study the defect chemistry, Na ion diffusion paths, and dopant properties in sodium iron phosphate [Na3Fe2(PO4)3] cathode material. The lowest intrinsic defect energy process (0.45 eV/defect) [...] Read more.
In this work, we employ computational modeling techniques to study the defect chemistry, Na ion diffusion paths, and dopant properties in sodium iron phosphate [Na3Fe2(PO4)3] cathode material. The lowest intrinsic defect energy process (0.45 eV/defect) is calculated to be the Na Frenkel, which ensures the formation of Na vacancies required for the vacancy-assisted Na ion diffusion. A small percentage of Na-Fe anti-site defects would be expected in Na3Fe2(PO4)3 at high temperatures. Long-range diffusion of Na is found to be low and its activation energy is calculated to be 0.45 eV. Isovalent dopants Sc, La, Gd, and Y on the Fe site are exoergic, meaning that they can be substituted experimentally and should be examined further. The formation of Na vacancies and Na interstitials in this material can be facilitated by doping with Zr on the Fe site and Si on the P site, respectively. Full article
(This article belongs to the Section Energy Materials)
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Open AccessArticle
A Comparative Study of Experimental Configurations in Synchrotron Pair Distribution Function
Materials 2019, 12(8), 1347; https://doi.org/10.3390/ma12081347
Received: 29 March 2019 / Revised: 22 April 2019 / Accepted: 23 April 2019 / Published: 25 April 2019
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Abstract
The identification and quantification of amorphous components and nanocrystalline phases with very small crystal sizes, smaller than ~3 nm, within samples containing crystalline phases is very challenging. However, this is important as there are several types of systems that contain these matrices: building [...] Read more.
The identification and quantification of amorphous components and nanocrystalline phases with very small crystal sizes, smaller than ~3 nm, within samples containing crystalline phases is very challenging. However, this is important as there are several types of systems that contain these matrices: building materials, glass-ceramics, some alloys, etc. The total scattering synchrotron pair distribution function (PDF) can be used to characterize the local atomic order of the nanocrystalline components and to carry out quantitative analyses in complex mixtures. Although the resolution in momentum transfer space has been widely discussed, the resolution in the interatomic distance space has not been discussed to the best of our knowledge. Here, we report synchrotron PDF data collected at three beamlines in different experimental configurations and X-ray detectors. We not only discuss the effect of the resolution in Q-space, Qmax ins of the recorded data and Qmax of the processed data, but we also discuss the resolution in the interatomic distance (real) space. A thorough study of single-phase crystalline nickel used as standard was carried out. Then, selected cement-related samples including anhydrous tricalcium and dicalcium silicates, and pastes derived from the hydration of tricalcium silicate and ye’elimite with bassanite were analyzed. Full article
(This article belongs to the Section Construction and Building Materials)
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Open AccessFeature PaperArticle
Nitrogen-Doped Superporous Activated Carbons as Electrocatalysts for the Oxygen Reduction Reaction
Materials 2019, 12(8), 1346; https://doi.org/10.3390/ma12081346
Received: 3 March 2019 / Revised: 13 April 2019 / Accepted: 23 April 2019 / Published: 25 April 2019
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Abstract
Nitrogen-containing superporous activated carbons were prepared by chemical polymerization of aniline and nitrogen functionalization by organic routes. The resulting N-doped carbon materials were carbonized at high temperatures (600–800 °C) in inert atmosphere. X-ray Photoelectron Spectroscopy (XPS) revealed that nitrogen amount ranges from 1 [...] Read more.
Nitrogen-containing superporous activated carbons were prepared by chemical polymerization of aniline and nitrogen functionalization by organic routes. The resulting N-doped carbon materials were carbonized at high temperatures (600–800 °C) in inert atmosphere. X-ray Photoelectron Spectroscopy (XPS) revealed that nitrogen amount ranges from 1 to 4 at.% and the nature of the nitrogen groups depends on the treatment temperature. All samples were assessed as electrocatalysts for the oxygen reduction reaction (ORR) in alkaline solution (0.1 M KOH) in order to understand the role of well-developed microporosity as well as the different nitrogen functionalities on the electrocatalytic performance in ORR. It was observed that nitrogen groups generated at high temperatures were highly selective towards the water formation. Among the investigated samples, polyaniline-derived activated carbon carbonized at 800 °C displayed the best performance (onset potential of 0.88 V versus RHE and an electron transfer number of 3.4), which was attributed to the highest concentration of N–C–O sites. Full article
(This article belongs to the Special Issue Advanced Carbon Materials For Catalytical Applications)
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Open AccessArticle
Microwave Sintering of SiAlON Ceramics with TiN Addition
Materials 2019, 12(8), 1345; https://doi.org/10.3390/ma12081345
Received: 28 March 2019 / Revised: 17 April 2019 / Accepted: 24 April 2019 / Published: 25 April 2019
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Abstract
α-β SiAlON/TiN composites with nominal composition of α:β = 25:75 were fabricated by microwave sintering. The effect of titanium nitride addition on the phases, microstructure, microwave absorption ability and mechanical properties (Vickers hardness and fracture toughness) of the SiAlON-based composites were studied. Finite [...] Read more.
α-β SiAlON/TiN composites with nominal composition of α:β = 25:75 were fabricated by microwave sintering. The effect of titanium nitride addition on the phases, microstructure, microwave absorption ability and mechanical properties (Vickers hardness and fracture toughness) of the SiAlON-based composites were studied. Finite Difference Time Domain (FDTD) software was used for the numerical simulation in order to assess the most suitable experimental setup. Sintering trials were performed in a single mode microwave furnace operating at 2.45 GHz and a power output of 660 W, for a reaction time of 30 min. SiC blocks were used as a susceptor to accelerate the microwave processing by hybrid heating, with reduced heat losses from the surface of the material of the α-β SiAlON/TiN composites. The optimum comprehensive mechanical properties, corresponding to a relative density of 96%, Vickers hardness of 12.98 ± 1.81 GPa and Vickers indentation fracture toughness of 5.52 ± 0.71 MPa.m1/2 were obtained at 850 °C when the content of TiN was 5 wt.%. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessArticle
Investigating the Mechanical Properties of ZrO2-Impregnated PMMA Nanocomposite for Denture-Based Applications
Materials 2019, 12(8), 1344; https://doi.org/10.3390/ma12081344
Received: 28 March 2019 / Revised: 18 April 2019 / Accepted: 20 April 2019 / Published: 25 April 2019
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Abstract
Acrylic resin PMMA (poly-methyl methacrylate) is used in the manufacture of denture bases but its mechanical properties can be deficient in this role. This study investigated the mechanical properties (flexural strength, fracture toughness, impact strength, and hardness) and fracture behavior of a commercial, [...] Read more.
Acrylic resin PMMA (poly-methyl methacrylate) is used in the manufacture of denture bases but its mechanical properties can be deficient in this role. This study investigated the mechanical properties (flexural strength, fracture toughness, impact strength, and hardness) and fracture behavior of a commercial, high impact (HI), heat-cured denture base acrylic resin impregnated with different concentrations of yttria-stabilized zirconia (ZrO2) nanoparticles. Six groups were prepared having different wt% concentrations of ZrO2 nanoparticles: 0% (control), 1.5%, 3%, 5%, 7%, and 10%, respectively. Flexural strength and flexural modulus were measured using a three-point bending test and surface hardness was evaluated using the Vickers hardness test. Fracture toughness and impact strength were evaluated using a single edge bending test and Charpy impact instrument. The fractured surfaces of impact test specimens were also observed using a scanning electron microscope (SEM). Statistical analyses were conducted on the data obtained from the experiments. The mean flexural strength of ZrO2/PMMA nanocomposites (84 ± 6 MPa) at 3 wt% zirconia was significantly greater than that of the control group (72 ± 9 MPa) (p < 0.05). The mean flexural modulus was also significantly improved with different concentrations of zirconia when compared to the control group, with 5 wt% zirconia demonstrating the largest (23%) improvement. The mean fracture toughness increased in the group containing 5 wt% zirconia compared to the control group, but it was not significant. However, the median impact strength for all groups containing zirconia generally decreased when compared to the control group. Vickers hardness (HV) values significantly increased with an increase in ZrO2 content, with the highest values obtained at 10 wt%, at 0 day (22.9 HV0.05) in dry conditions when compared to the values obtained after immersing the specimens for seven days (18.4 HV0.05) and 45 days (16.3 HV0.05) in distilled water. Incorporation of ZrO2 nanoparticles into high impact PMMA resin significantly improved flexural strength, flexural modulus, fracture toughness and surface hardness, with an optimum concentration of 3–5 wt% zirconia. However, the impact strength of the nanocomposites decreased, apart from the 5 wt% zirconia group. Full article
(This article belongs to the Special Issue Advanced Composite Biomaterials)
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Open AccessArticle
Simulation and Experimental Study on Residual Stress Distribution in Titanium Alloy Treated by Laser Shock Peening with Flat-Top and Gaussian Laser Beams
Materials 2019, 12(8), 1343; https://doi.org/10.3390/ma12081343
Received: 24 March 2019 / Revised: 15 April 2019 / Accepted: 22 April 2019 / Published: 24 April 2019
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Abstract
The residual stress introduced by laser shock peening (LSP) is one of the most important factors in improving metallic fatigue life. The shock wave pressure has considerable influence on residual stress distribution, which is affected by the distribution of laser energy. In this [...] Read more.
The residual stress introduced by laser shock peening (LSP) is one of the most important factors in improving metallic fatigue life. The shock wave pressure has considerable influence on residual stress distribution, which is affected by the distribution of laser energy. In this work, a titanium alloy is treated by LSP with flat-top and Gaussian laser beams, and the effects of spatial energy distribution on residual stress are investigated. Firstly, a 3D finite element model (FEM) is developed to predict residual stress with different spatial energy distribution, and the predicted residual stress is validated by experimental data. Secondly, three kinds of pulse energies, 3 J, 4 J and 5 J, are chosen to study the difference of residual stress introduced by flat-top and Gaussian laser beams. Lastly, the effect mechanism of spatial energy distribution on residual stress is revealed. Full article
(This article belongs to the Special Issue Intense Optical Pulse Processing)
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Open AccessArticle
Push-Pull Chromophores Based on the Naphthalene Scaffold: Potential Candidates for Optoelectronic Applications
Materials 2019, 12(8), 1342; https://doi.org/10.3390/ma12081342
Received: 5 April 2019 / Revised: 19 April 2019 / Accepted: 22 April 2019 / Published: 24 April 2019
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Abstract
A series of ten push-pull chromophores comprising 1H-cyclopenta[b]naphthalene-1,3(2H)-dione as the electron-withdrawing group have been designed, synthesized, and characterized by UV-visible absorption and fluorescence spectroscopy, cyclic voltammetry and theoretical calculations. The solvatochromic behavior of the different dyes has [...] Read more.
A series of ten push-pull chromophores comprising 1H-cyclopenta[b]naphthalene-1,3(2H)-dione as the electron-withdrawing group have been designed, synthesized, and characterized by UV-visible absorption and fluorescence spectroscopy, cyclic voltammetry and theoretical calculations. The solvatochromic behavior of the different dyes has been examined in 23 solvents and a positive solvatochromism has been found for all dyes using the Kamlet-Taft solvatochromic relationship, demonstrating the polar form to be stabilized in polar solvents. To establish the interest of this polyaromatic electron acceptor only synthesizable in a multistep procedure, a comparison with the analog series based on the benchmark indane-1,3-dione (1H-indene-1,3(2H)-dione) has been done. A significant red-shift of the intramolecular charge transfer band has been found for all dyes, at a comparable electron-donating group. Parallel to the examination of the photophysical properties of the different chromophores, a major improvement of the synthetic procedure giving access to 1H-cyclopenta[b]naphthalene-1,3(2H)-dione has been achieved. Full article
(This article belongs to the Special Issue Advances and Challenges in Organic Electronics)
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Open AccessArticle
Hydrogen Embrittlement and Improved Resistance of Al Addition in Twinning-Induced Plasticity Steel: First-Principles Study
Materials 2019, 12(8), 1341; https://doi.org/10.3390/ma12081341
Received: 14 January 2019 / Revised: 19 April 2019 / Accepted: 22 April 2019 / Published: 24 April 2019
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Abstract
Understanding the mechanism of hydrogen embrittlement (HE) of austenitic steels and developing an effective strategy to improve resistance to HE are of great concern but challenging. In this work, first-principles studies were performed to investigate the HE mechanism and the improved resistance of [...] Read more.
Understanding the mechanism of hydrogen embrittlement (HE) of austenitic steels and developing an effective strategy to improve resistance to HE are of great concern but challenging. In this work, first-principles studies were performed to investigate the HE mechanism and the improved resistance of Al-containing austenite to HE. Our results demonstrate that interstitial hydrogen atoms have different site preferences in Al-free and Al-containing austenites. The calculated binding energies and diffusion barriers of interstitial hydrogen atoms in Al-containing austenite are remarkably higher than those in Al-free austenite, indicating that the presence of Al is more favorable for reducing hydrogen mobility. In Al-free austenite, interstitial hydrogen atoms caused a remarkable increase in lattice compressive stress and a distinct decrease in bulk, shear, and Young’s moduli. Whereas in Al-containing austenite, the lattice compressive stress and the mechanical deterioration induced by interstitial hydrogen atoms were effectively suppressed. Full article
(This article belongs to the Section Corrosion and Materials Degradation)
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Open AccessArticle
Characterization of Cementation Factor of Unconsolidated Granular Materials Through Time Domain Reflectometry with Variable Saturated Conditions
Materials 2019, 12(8), 1340; https://doi.org/10.3390/ma12081340
Received: 15 March 2019 / Revised: 20 April 2019 / Accepted: 22 April 2019 / Published: 24 April 2019
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Abstract
The cementation factor is necessary to determine porosity via the Archie equation, and its range of values has been suggested in many previous studies. However, the cementation factors in the literature are limited to fully saturated conditions, and it may thus be inaccurate [...] Read more.
The cementation factor is necessary to determine porosity via the Archie equation, and its range of values has been suggested in many previous studies. However, the cementation factors in the literature are limited to fully saturated conditions, and it may thus be inaccurate to use the same value in other saturation conditions. The objective of this study is to characterize how the cementation factor varies depending on the saturation percentage. In this study, glass beads and soil are selected as the specimens, and two relative density values, 40% and 80%, are selected. Time domain reflectometry (TDR) is used to obtain both the saturation and electrical resistivity of the specimens. TDR is installed in the cell, and fluid is continuously circulated from the bottom to the top of the porous material for 30 min. The estimated saturation increases with time and the electrical resistivity is reduced during the circulation. Finally, the cementation factor at every saturated stage is determined, and the error ratio based on the porosity is calculated to show the importance of the cementation factor. The results show that there is a high error ratio when an unsuitable cementation factor that does not consider the saturation condition is used. This study demonstrates that the method for determining the actual cementation factor using TDR and the Archie equation can be applied in various saturation conditions. Full article
(This article belongs to the Section Porous Materials)
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Open AccessArticle
Experimental and Theoretical Studies on the Corrosion Inhibition of Carbon Steel by Two Indazole Derivatives in HCl Medium
Materials 2019, 12(8), 1339; https://doi.org/10.3390/ma12081339
Received: 2 April 2019 / Revised: 23 April 2019 / Accepted: 23 April 2019 / Published: 24 April 2019
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Abstract
In this work, two indazole derivatives, namely 5-aminoindazole (AIA) and 5-nitroindazole (NIA), were investigated as corrosion inhibitors for carbon steel in 1 M HCl solution by experimental and density functional theory (DFT) methods. The electrochemical results indicate that the inhibition ability follows the [...] Read more.
In this work, two indazole derivatives, namely 5-aminoindazole (AIA) and 5-nitroindazole (NIA), were investigated as corrosion inhibitors for carbon steel in 1 M HCl solution by experimental and density functional theory (DFT) methods. The electrochemical results indicate that the inhibition ability follows the order of AIA > NIA, which is due to the stronger electron-donating effect of –NH2 of the AIA group than the –NO2 group of NIA. Besides, the frontier orbital theory shows that the AIA exhibits higher reaction activity than NIA, and a more negative adsorption energy for AIA was also obtained, which is consistent with the analysis of the electrochemical measurements. We draw the conclusion that the electron-donating effect makes it easier for AIA to donate electrons to iron atoms to form a stronger protective layer than NIA. Full article
(This article belongs to the Special Issue Recent Advances in Corrosion Science)
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Open AccessArticle
Characterization of Ablated Bone and Muscle for Long-Pulsed Laser Ablation in Dry and Wet Conditions
Materials 2019, 12(8), 1338; https://doi.org/10.3390/ma12081338
Received: 1 April 2019 / Revised: 17 April 2019 / Accepted: 18 April 2019 / Published: 24 April 2019
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Abstract
Smart laser technologies are desired that can accurately cut and characterize tissues, such as bone and muscle, with minimal thermal damage and fast healing. Using a long-pulsed laser with a 0.5–10 ms pulse width at a wavelength of 1.07 µm, we investigated the [...] Read more.
Smart laser technologies are desired that can accurately cut and characterize tissues, such as bone and muscle, with minimal thermal damage and fast healing. Using a long-pulsed laser with a 0.5–10 ms pulse width at a wavelength of 1.07 µm, we investigated the optimum laser parameters for producing craters with minimal thermal damage under both wet and dry conditions. In different tissues (bone and muscle), we analyzed craters of various morphologies, depths, and volumes. We used a two-way Analysis of Variance (ANOVA) test to investigate whether there are significant differences in the ablation efficiency in wet versus dry conditions at each level of the pulse energy. We found that bone and muscle tissue ablated under wet conditions produced fewer cracks and less thermal damage around the craters than under dry conditions. In contrast to muscle, the ablation efficiency of bone under wet conditions was not higher than under dry conditions. Tissue differentiation was carried out based on measured acoustic waves. A Principal Component Analysis of the measured acoustic waves and Mahalanobis distances were used to differentiate bone and muscle under wet conditions. Bone and muscle ablated in wet conditions demonstrated a classification error of less than 6.66% and 3.33%, when measured by a microphone and a fiber Bragg grating, respectively. Full article
(This article belongs to the Special Issue Advances in Laser Technologies and Applications)
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Open AccessArticle
Analysis and Modelling of Non-Fourier Heat Behavior Using the Wavelet Finite Element Method
Materials 2019, 12(8), 1337; https://doi.org/10.3390/ma12081337
Received: 1 April 2019 / Revised: 21 April 2019 / Accepted: 23 April 2019 / Published: 24 April 2019
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Abstract
Non-Fourier heat behavior is an important issue for film material. The phenomenon is usually observed in some laser induced thermal responses. In this paper, the non-Fourier heat conduction problems with temperature and thermal flux relaxations are investigated based on the wavelet finite element [...] Read more.
Non-Fourier heat behavior is an important issue for film material. The phenomenon is usually observed in some laser induced thermal responses. In this paper, the non-Fourier heat conduction problems with temperature and thermal flux relaxations are investigated based on the wavelet finite element method and solved by the central difference scheme for one- and two-dimensional media. The Cattaneo–Vernotte model and the Dual-Phase-Lagging model are used for finite element formulation, and a new wavelet finite element solving formulation is proposed to address the memory requirement problem. Compared with the current methodologies for the Cattaneo–Vernotte model and the Dual-Phase-Lagging model, the present model is a direct one which describe the thermal behavior by one equation about temperature. Compared with the wavelet method proposed by Xiang et al., the developed method can be used for arbitrary shapes. In order to address the efficient computation problems for the Dual-Phase-Lagging model, a novel iteration updating methodology is also proposed. The proposed iteration algorithms on time avoids the use the global stiffness matrix, which allows the efficient calculation for title issue. Numerical calculations have been conducted in the manner of comparisons with the classical finite element method and spectral finite element method. The comparisons from accuracy, efficiency, flexibility, and applicability validate the developed method to be an effective and alternative tool for material thermal analysis. Full article
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Open AccessArticle
Non-Precious Electrodes for Practical Alkaline Water Electrolysis
Materials 2019, 12(8), 1336; https://doi.org/10.3390/ma12081336
Received: 4 April 2019 / Revised: 16 April 2019 / Accepted: 19 April 2019 / Published: 24 April 2019
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Abstract
Water electrolysis is a promising approach to hydrogen production from renewable energy sources. Alkaline water electrolyzers allow using non-noble and low-cost materials. An analysis of common assumptions and experimental conditions (low concentrations, low temperature, low current densities, and short-term experiments) found in the [...] Read more.
Water electrolysis is a promising approach to hydrogen production from renewable energy sources. Alkaline water electrolyzers allow using non-noble and low-cost materials. An analysis of common assumptions and experimental conditions (low concentrations, low temperature, low current densities, and short-term experiments) found in the literature is reported. The steps to estimate the reaction overpotentials for hydrogen and oxygen reactions are reported and discussed. The results of some of the most investigated electrocatalysts, namely from the iron group elements (iron, nickel, and cobalt) and chromium are reported. Past findings and recent progress in the development of efficient anode and cathode materials appropriate for large-scale water electrolysis are presented. The experimental work is done involving the direct-current electrolysis of highly concentrated potassium hydroxide solutions at temperatures between 30 and 100 °C, which are closer to industrial applications than what is usually found in literature. Stable cell components and a good performance was achieved using Raney nickel as a cathode and stainless steel 316L as an anode by means of a monopolar cell at 75 °C, which ran for one month at 300 mA cm−2. Finally, the proposed catalysts showed a total kinetic overpotential of about 550 mV at 75 °C and 1 A cm−2. Full article
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Open AccessArticle
Parametric Optimization of Trochoidal Step on Surface Roughness and Dish Angle in End Milling of AISID3 Steel Using Precise Measurements
Materials 2019, 12(8), 1335; https://doi.org/10.3390/ma12081335
Received: 1 April 2019 / Revised: 21 April 2019 / Accepted: 23 April 2019 / Published: 24 April 2019
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Abstract
Tool steel play a vital role in modern manufacturing industries due to its excellent properties. AISI D3 is a cold work tool steel which possess high strength, more hardenability and good wear resistance properties. It has a wide variety of applications in automobile [...] Read more.
Tool steel play a vital role in modern manufacturing industries due to its excellent properties. AISI D3 is a cold work tool steel which possess high strength, more hardenability and good wear resistance properties. It has a wide variety of applications in automobile and tool and die making industries such as blanking and forming tools, high stressed cutting, deep drawing and press tools. The novel ways of machining these steels and finding out the optimum process parameters to yield good output is of practical importance in the field of research. This research work explores an attempt to identify the optimized process parameter combinations in end milling of AISI D3 steel to yield low surface roughness and maximum dish angle using trochoidal milling tool path, which is considered as a novelty in this study. 20 experimental trials based on face centered central composite design (CCD) of response surface methodology (RSM) were executed by varying the input process factors such as cutting speed, feed rate and trochoidal step. Analysis of variance (ANOVA) was adopted to study the significance of selected process parameters and its relative interactions on the performance measures. Desirability-based multiple objective optimization was performed and the mathematical models were developed for prediction purposes. The developed mathematical model was statistically significant with optimum conditions of cutting speed of 41m/min, feed rate of 120 mm/min and trochoidal step of 0.9 mm. It was also found that the deviation between the experimental and predicted values is 6.10% for surface roughness and 1.33% for dish angle, respectively. Full article
(This article belongs to the Special Issue Machining—Recent Advances, Applications and Challenges)
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Open AccessArticle
Old Molecule, New Chemistry: Exploring Silicon Phthalocyanines as Emerging N-Type Materials in Organic Electronics
Materials 2019, 12(8), 1334; https://doi.org/10.3390/ma12081334
Received: 10 April 2019 / Revised: 18 April 2019 / Accepted: 20 April 2019 / Published: 24 April 2019
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Abstract
Efficient synthesis of silicon phthalocyanines (SiPc) eliminating the strenuous reaction conditions and hazardous reagents required by classical methods is described. Implementation into organic thin-film transistors (OTFTs) affords average electron field-effect mobility of 3.1 × 10−3 cm2 V−1 s−1 and [...] Read more.
Efficient synthesis of silicon phthalocyanines (SiPc) eliminating the strenuous reaction conditions and hazardous reagents required by classical methods is described. Implementation into organic thin-film transistors (OTFTs) affords average electron field-effect mobility of 3.1 × 10−3 cm2 V−1 s−1 and threshold voltage of 25.6 V for all synthetic routes. These results demonstrate that our novel chemistry can lead to high performing SiPc-based n-type OTFTs. Full article
(This article belongs to the Special Issue Advances and Challenges in Organic Electronics)
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Open AccessArticle
A Study on the Dimension Accuracy on the Inner Structure of the 3D Printed Parts Caused by the Scanning Strategy
Materials 2019, 12(8), 1333; https://doi.org/10.3390/ma12081333
Received: 11 March 2019 / Revised: 22 April 2019 / Accepted: 22 April 2019 / Published: 24 April 2019
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Abstract
Selective laser melting (SLM) has been used in many fields recently, especially in the aerospace field. Many studies have been done on mechanical properties of the printed parts, but the dimension accuracy of the inner structure received little attention during these years. In [...] Read more.
Selective laser melting (SLM) has been used in many fields recently, especially in the aerospace field. Many studies have been done on mechanical properties of the printed parts, but the dimension accuracy of the inner structure received little attention during these years. In this work, the dimension accuracy of the inner structure was measured and compared using different scanning strategies. Compared with the measured data, a new scanning strategy was used and finds that the dimension accuracy was better than the previous one that used a two-scanning strategy. To explain this phenomenon, finite element analysis (FEA) was used to show the temperature distribution after a 0.1 s cooling using two different scanning strategies, which caused the dimensional deviation in printing. Full article
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Open AccessArticle
TiO2 Self-Assembled, Thin-Walled Nanotube Arrays for Photonic Applications
Materials 2019, 12(8), 1332; https://doi.org/10.3390/ma12081332
Received: 25 March 2019 / Revised: 16 April 2019 / Accepted: 18 April 2019 / Published: 24 April 2019
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Abstract
Two-dimensional arrays of hollow nanotubes made of TiO2 are a promising platform for sensing, spectroscopy and light harvesting applications. Their straightforward fabrication via electrochemical anodization, growing nanotube pillars of finite length from a Ti foil, allows precise tailoring of geometry and, thus, [...] Read more.
Two-dimensional arrays of hollow nanotubes made of TiO 2 are a promising platform for sensing, spectroscopy and light harvesting applications. Their straightforward fabrication via electrochemical anodization, growing nanotube pillars of finite length from a Ti foil, allows precise tailoring of geometry and, thus, material properties. We theoretically investigate these photonic crystal structures with respect to reduction of front surface reflection, achievable field enhancement, and photonic bands. Employing the Rigorous Coupled Wave Analysis (RCWA), we study the optical response of photonic crystals made of thin-walled nanotubes relative to their bare Ti foil substrate, including under additional charge carrier doping which might occur during the growth process. Full article
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Open AccessArticle
Determination of the Enhancement or Shielding Interaction between Two Parallel Cracks under Fatigue Loading
Materials 2019, 12(8), 1331; https://doi.org/10.3390/ma12081331
Received: 20 March 2019 / Revised: 11 April 2019 / Accepted: 22 April 2019 / Published: 24 April 2019
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Abstract
In this paper, the interactions between two parallel cracks are investigated experimentally and numerically. Finite element models have been established to obtain the stress intensity factors and stress distributions of the parallel cracks with different positions and sizes. Fatigue crack growth tests of [...] Read more.
In this paper, the interactions between two parallel cracks are investigated experimentally and numerically. Finite element models have been established to obtain the stress intensity factors and stress distributions of the parallel cracks with different positions and sizes. Fatigue crack growth tests of 304 stainless steel specimens with the single crack and two parallel cracks have been conducted to confirm the numerical results. The numerical analysis results indicate that the interactions between the two parallel cracks have an enhancement or shielding effect on the stress intensity factors, depending on the relative positions of the cracks. The criterion diagram to determine the enhancement or shielding effect between two parallel cracks is obtained. The changes of the stress fields around the cracks have been studied to explain the mechanism of crack interactions. Full article
(This article belongs to the Special Issue Damage and Mechanical Properties of Steels)
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Open AccessArticle
In Vivo Evaluation of the Genotoxic Effects of Poly (Butylene adipate-co-terephthalate)/Polypyrrole with Nanohydroxyapatite Scaffolds for Bone Regeneration
Materials 2019, 12(8), 1330; https://doi.org/10.3390/ma12081330
Received: 6 March 2019 / Revised: 11 April 2019 / Accepted: 13 April 2019 / Published: 24 April 2019
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Abstract
Here, butylene adipate-co-terephthalate/polypyrrole with nanohydroxyapatite (PBAT/PPy/nHAp) scaffolds were fabricated and characterized. The electrospinning process was carried out using 12 kV, a needle of 23 G, an infusion pump set at 0.3 mL/h, and 10 cm of distance. Afterwards, nHAp was directly electrodeposited onto [...] Read more.
Here, butylene adipate-co-terephthalate/polypyrrole with nanohydroxyapatite (PBAT/PPy/nHAp) scaffolds were fabricated and characterized. The electrospinning process was carried out using 12 kV, a needle of 23 G, an infusion pump set at 0.3 mL/h, and 10 cm of distance. Afterwards, nHAp was directly electrodeposited onto PBAT/PPy scaffolds using a classical three-electrode apparatus. For in vivo assays (comet assay, acute and chronic micronucleus), 60 male albino Wistar rats with 4 groups were used in each test (n = 5): PBAT/PPy; PBAT/PPy/nHAp; positive control (cyclophosphamide); and the negative control (distilled water). Peripheral blood samples were collected from the animals to perform the comet test after 4 h (for damage) and 24 h (for repair). In the comet test, it was shown that the scaffolds did not induce damage to the % DNA tail and neither for tail length. After the end of 48 h (for acute micronucleus) and 72 h (for chronic micronucleus), bone marrow was collected from each rat to perform the micronucleus test. All of the produced scaffolds did not present genotoxic effects, providing strong evidence for the biological application of PBAT/PPy/nHAp scaffolds. Full article
(This article belongs to the Special Issue Surface Modification of Functional Scaffolds and Biomaterials)
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