查看更多>>摘要：? 2022 Elsevier B.V.Magnesium alloys have become promising biomedical metal materials because of their biocompatibility, degradability, and good mechanical properties. However, the rapid degradation of magnesium alloys and its associated effects have limited the applications of magnesium alloys. Alloying and preparation processes can reduce the degradation rate by changing the microstructure of magnesium alloys, such as grain size, porosity, formation of intermetallic compounds/second phases, etc. In this paper, the in vitro and in vivo degradation of magnesium alloys were reviewed in terms of degradation mechanism, influencing factors, and corrosion products. Composition design and manufacturing process were mainly discussed for controlling the degradation, and surface treatment and structural design were briefly described as control methods of degradation. This helps achieve the goal of controlled and predictable degradation rate of magnesium alloys.
查看更多>>摘要：? 2022 Elsevier B.V.The luminescence properties of yttrium aluminum garnet doped with variable chromium concentration were investigated under namely three different excitation wavelengths – 275 nm, 440 nm, and 580 nm. It was discerned that under 440 nm and 580 nm excitation, spin forbidden 2E→4A2 transition shows a typical trend of increasing emission intensity with concentration increase in the range of 320–900 nm. Whereas, when the compounds with an increasing nominal dopant concentration were excited with 275 nm radiation, an exponential decrease in emission intensity of spin allowed 4T2→4A2 transition (in the range of 700–1000 nm) was observed. It was demonstrated that the emission of a single compound with one dopant exhibits emission in almost half of the NIR region.
查看更多>>摘要：? 2022 Elsevier B.V.Bismuth ferrite has recently been extensively studies as potential material for photovoltaic and photocatalytic applications as it provides wide opportunity to tune band-gap by site engineering with suitable elements. Further, this doping modified the optical and ferroelectric properties of bismuth ferrite for the applications. Rare-earth (Gd) and transition-element (Mn, Co and Cr) co-doped samples of bismuth ferrite have been synthesized by the sol-gel technique at low temperature. Structural characterization using X-ray diffraction reveals a phase transformation from rhombohedral to orthorhombic with co-doping in pure BFO sample. A reduction of grain size for doped bismuth ferrites samples is observed in SEM analysis. The dielectric properties get enhanced with co-doping due to decrease in the Fe2+ ions and oxygen vacancies. Increase in the remnant polarization was obtained in doped BFO samples and maximum Pr～1.615μC/cm2 for Gd doped BFO sample. Decrease in band-gap values with doping has been observed from (2.35–1.90 eV). Power conversion efficiency has been calculated with doping of different substances which results in improved photovoltaic properties with respect to pure BFO (η% ～0.00039–0.026). Also, photocatalytic studies have been done for all the samples of BFO. Enhanced values of photocatalytic efficiency (η% ～90.89–96.08) has been observed with co-doping of rare earth and transition elements in bismuth ferrites. Thus, co-doping of rare-earth and transition-element in bismuth ferrite can improve multiferroic, ferroelectric, photovoltaic and photocatalytic properties for different applications.
查看更多>>摘要：? 2022 Elsevier B.V.Electrochemical water splitting for hydrogen production is of great significance in exploring sustainable energy for the upcoming low-carbon era, the discovery of electrocatalysts with high activity and inexpensive is highly important to expedite the extremely sluggish kinetics of oxygen evolution reaction (OER). Herein, an efficient OER electrocatalyst was designed by doping trace Fe into Ni2P via a simple structural transformation. The crystal structure and surface chemical state analysis demonstrated the introduction of Fe dopant and the successful formation of the host Ni2P. As-prepared Fe-Ni2P microspheres greatly optimized the intrinsic activity of the active site and accelerated the mass transfer rate. Intriguingly, the electrochemical tests certified that trace Fe doping can increase the activity of nickel phosphide more significantly. High valence state transition from Ni[sbnd]P bond to Ni[sbnd]O bond was clearly observed, suggesting the new active species can be easily formed during OER. This article provides a trace Fe doping strategy for the study of efficient electrocatalysts to improve the kinetics of OER.
查看更多>>摘要：? 2022 Elsevier B.V.Half Heusler(hH) compounds have demonstrated exceptional capability in a wide range of functional applications as semiconductors. Although there are theoretical predictions about newer compounds and their thermodynamic stability, experimental validation is often missing. In this study, we report two quaternary multicomponent Zr-based hH alloy systems, namely ZrNi0.5Fe0.5Sb and ZrNiIn0.5Sb0.5, designed by combining 19 and 17 VEC (valence electron count) alloy systems. The structural features, including the crystal structures and compositions, were established using multiple techniques like X-ray diffraction, scanning and transmission electron microscopy. Both these systems crystallized in signature hH cubic structure (F43?m) having lattice parameters 0.6091 nm and 0.6104 nm, respectively. The measurement of Seebeck coefficients over a wide temperature range showed p-to n-type semiconductor transition in ZrNi0.5Fe0.5Sb at around 888 K due to bipolar conduction. Subsequently, the partial substitution of Co for Fe sites (ZnNi0.5Fe0.3Co0.2Sb) completely suppressed the bipolar conductivity, making it a n-type semiconductor and increased the absolute value of Seebeck coefficient, by an order of magnitude, to ? 133μV/K. The alloy ZrNiIn0.5Sb0.5 showed n-type semiconductor behavior throughout the measurement temperature range. This study conducts an in-depth examination of the microstructural phase evolution, chemical environment of the elements forming the novel hH phase and demonstrates the tunability of electronic properties through aliovalent substitutions at various lattice sites.
查看更多>>摘要：? 2022 Elsevier B.V.To solve the existing problems in the hydrogen storage properties of Ti-Cr-Mn based hydrogen storage alloys, the effects of different elements (M = Fe, Ni, Co) on the phase structure and hydrogen storage properties of Ti-Zr-Cr-Mn-V-M alloy are studied. M elements increase the plateau pressure of hydrogen absorption and desorption, and the plateau pressure of Ti0.8Zr0.2Mn0.9Cr0.6V0.3Co0.2 is the highest and that of Ti0.8Zr0.2Mn0.9Cr0.6V0.3Ni0.2 is the lowest. It is found that the substitution of Fe is very effective in improving dynamic performance and hydrogen storage capacity. Ti0.8Zr0.2Mn0.9Cr0.6V0.3Fe0.2 alloy also shows excellent plateau performance with very small hysteresis and sloping which is attributed to the interstitial size effect. Ti0.8Zr0.2Mn0.9Cr0.6V0.3Fe0.2 alloy has a hydrogen desorption pressure of 0.34 MPa at 303 K and can release 1.75 wt% hydrogen within 200 s. The material with higher mass density and lower dehydrogenation temperature can apply to hydrogen storage and hydrogen transportation.
查看更多>>摘要：? 2022 Elsevier B.V.The microwave-assisted titanium nitride (TiN) coating method using TiN powders as a raw material was investigated for hard and smooth TiN coatings by decreasing the energy of the exothermic reaction between the raw powder and air. A titanium-aluminum-vanadium alloy (Ti-6Al-4 V) substrate was buried in TiN powders and irradiated with 2.45 GHz microwaves using a multimode cavity. After microwave processing, TiN films were found to be successfully deposited on the Ti-6Al-4 V substrate without atmospheric control. X-ray diffraction results indicated that face-centered cubic (fcc)-TiN phase increased with increasing temperature. TiN coating films synthesized at 900 °C and 800 °C were smoother than those at 1000 °C. Besides, the TiN films synthesized at 900 °C exhibited 697 HV with arithmetic mean roughness (Ra) = 0.29. These results demonstrated that a hard and smooth TiN film can be obtained using TiN powders as raw materials.
查看更多>>摘要：? 2022 Elsevier B.V.Although halide perovskites have significant potential for flexible devices, the bending mechanical behavior of halide thin films has not been investigated in detail. Herein, we report the quantitative bending fracture behavior of flexible methylammonium lead triiodide (MAPbI3) thin films encapsulated with an overlayer of either polystyrene (PS) or poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). The significantly retarded cracking behavior of the halide films demonstrated that adjusting the polymer overlayers with different thicknesses resulted in substantial mechanical enhancements. For example, the minimum strain for crack initiation was ~1.96% for a highly concentrated PS overlayer with a thickness of ~50 nm, which corresponds to an increase of ~40% relative to the non-encapsulated sample. In addition to quantifying the fracture behavior with fracture energy and film strength, the chemical effects of encapsulation were also investigated in terms of the phase dissolution of the perovskite, which was correlated with changes in the Hall electrical properties.
查看更多>>摘要：? 2022 Elsevier B.V.A high-entropy alloy coating of FeCoNiMnCu was prepared on SUS 430 steel via magnetron sputtering for solid oxide fuel cell (SOFC) interconnects application. The coated steels were subject to thermal exposure in air at 800 °C for up to 10 weeks. Phase constituents, microstructure and area specific resistance (ASR) of the coated steel before and after the oxidation testing were investigated. Results indicated the alloy coating was thermally converted into a high-entropy spinel coating of (Fe,Co,Ni,Mn,Cu)3O4 after oxidation and a protective Cr2O3 layer was formed at the steel/coating interface. The (Fe,Co,Ni,Mn,Cu)3O4 spinel coating effectively suppressed growth of Cr2O3 layer and outward diffusion of Cr during the long term exposure. Scale ASR of the coated steel was as low as 6.59 mΩ·cm2 at 800 °C after 10 weeks. It indicates that (Fe,Co,Ni,Mn,Cu)3O4 is a promising coating material for SOFC metallic interconnects.
查看更多>>摘要：? 2022 Elsevier B.V.W-Ni alloy has been an important engineering material in military, nuclear industry and many other fields because of its excellent properties such as high strength and superior heat/corrosion/oxidation resistances. As a mainstream additive manufacturing technology based on powder-bed-fusion principle, selective laser melting (SLM) is suitable for the rapid fabrication of very complex W-Ni alloy components. However, researches on the powder densification behavior and microstructure formation mechanism of SLM W-Ni alloy are not thorough enough. In this work, a series of W-xNi (x = 16, 23, 30 wt.%) binary alloy samples were fabricated by SLM, using W/Ni mixed powders as the raw materials. The densification behaviors of the W/Ni mixed powders and the microstructure formation mechanisms of the different SLM W-Ni samples were studied. The results showed that when the W/Ni mixed powder bed was scanned by the laser, Ni powders with a relatively lower melting point would melt completely whereas W powders with a relatively higher melting point would rearrange themselves in the liquid Ni and only part of them could be dissolved into the liquid Ni. As the initial content of Ni powders increased, the rearrangement and dissolution of W powders proceed more sufficiently, thus leading to the improvement in densification degree. The relative densities of the W-16Ni, W-23Ni and W-30Ni SLM samples are 92.87 ± 0.67%, 98.66 ± 0.26% and 99.67 ± 0.18%, respectively. During the solidification processes of W-Ni molten pools, the precipitation of W grains from liquid Ni, the transformation of liquid Ni to γ-Ni solid solution and the precipitation of Ni2W from γ-Ni solid solution would occur in sequence. For the W-16Ni and W-23Ni samples, the grain morphology of the W precipitations is dendritic. For the W-30Ni samples, the W precipitations are globular. As a result of the unique melting- solidification behaviors, all the SLM samples possessed a tri-modal microstructure composed of unmelted W particles, dendritic/globular W grains, and γ-Ni solid solution with Ni2W intragranular precipitation. The average microhardness of the SLM W-Ni alloy samples decreased with the increase of Ni content, which could be explained by the variation in defect and microstructure features.
NSTL
Elsevier