查看更多>>摘要：The microstructural evolution of K4750 nickel-based superalloy with different hafnium (Hf) contents was investigated by thermodynamic calculations (TC) and experiments. According to TC, with the increases of Hf content from 0 wt% to 1.5 wt%, the redissolving temperature of MC carbide first decreased rapidly and then tended to be relatively stable, the precipitated temperature of M23C6 carbide decreased gradually, while the gamma ' weight fraction increased first and then stabilized. Three alloys containing 0 wt%, 0.11 wt%, and 0.28 wt% Hf were then prepared to further study the evolution of the microstructure. The experimental results showed that the increase of Hf content changed the morphology of MC carbide from long strip to rodlike and blocky, which is caused by the decrease of Ti and Nb contents and the increase of Hf content in MC carbides. The addition of Hf also changed the morphology of M23C6 carbide from continuous to granular due to the different MC distribution at grain boundaries (GBs). In addition, a small amount of Hf segregated into the gamma ' phase, reducing the Al and Nb contents of the gamma ' phase, resulting in an increased gamma/gamma ' lattice mismatch. As the Hf content increased from 0 wt% to 0.11 wt% and 0.28 wt%, the mean stress rupture life at 750 degrees C and 430 MPa increased from 99.54 h to 105.73 h and 170.96 h, which was closely related to the evolution of MC, M23C6 and gamma ' precipitates. Therefore, the relationship between microstructure and stress rupture properties was discussed in detail.
查看更多>>摘要：The effect of MnCO3 additions on crystal structure, grain growth behavior, and dielectric properties were studied in the La2O3-doped BaTiO3 system. La2O3-doped BaTiO3 powders were prepared by conventional solid-state reaction routes and then after the addition of MnCO3, the powder compacts were sintered at 1250 degrees C in air. The tetragonality (c/a) of the samples increased with the amount of up to 0.5 mol% MnCO3 and then decreased above 0.5 mol%. The 3D grain shape became more spherical polygons with increasing amounts of MnCO3. The grain growth behavior changed from suppressed growth to abnormal grain growth and finally normal grain growth with increasing amounts of MnCO3 when the powder compacts were sintered. The correlation between the grain growth behavior and the grain shape change is discussed from the perspective of two-dimensional nucleation grain growth theory. Further, the dielectric properties are discussed in terms of the crystal structure, microstructural control, and charge compensation. (c) 2022 Published by Elsevier B.V.
查看更多>>摘要：One-dimensional (1D) hierarchical carbon nitrides nanorods (HCNNRs) mediated by cobalt was designed and synthesized using a template free hydrothermal approach for improving solar light assisted H(2 )evolution. The performance of 1D HCNNTs was significantly enhanced compared to bulk g-C(3)N4 due to larger active surface area, more visible light utilization and superior charge carrier along the unidirectional flow pathways. The 2% Co/HCNNRs (1D) exhibited excellent photocatalytic efficiency and optimal H-2 yield reached up to 620 mu mol g(-1), which is 11.27 and 17.71 folds more than it was attained with pure HCNNR and bulk g-C3N4, respectively. This reveals that 1D structure helps to accelerate charge transport, whereas, Co works as a mediator to trap electrons, thus improving photocatalytic performance. The crucial operating parameters such as sacrificial reagents, feed concentration and catalyst loading were further optimized based on highest H-2 evolution. Interestingly, mass transfer, charge transfer and amount of photoinduced charges were greatly dependent on the operating parameters. Higher methanol and lower TEOA concentration were beneficial to yield highest photoactivity and stability. This work provides new approach to construct template free 1D nanorods and would be beneficial to enhance performance in other solar energy related applications. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Perovskite solar cells (PSCs) have attracted great attentions due to their excellent photovoltaic performance. Further improvement of device efficiency is limited by the recombination of the charge carriers even a heterojunction-based architecture is employed. Herein, we discovered that a simple surface modification of the perovskite film by incorporating isopropyl alcohol (IPA) post-treatment could convert the top surface to be more n-type, which spontaneously formed an n/n(+) homojunction between the bulk (weak n type (n)) and the surface (more n-type (n(+))) in a single perovskite film. A reconstruction toward a PbI2-rich top surface was induced by the remove of excess formamidinium iodide dissolved in a polar solvent IPA. This reconstructed n/n(+) homojunction lead to the enlarged built-in electric field for efficient charge separation and transport of the photogenerated carriers. The inverted PSCs with the reconstructed n/n+ homojunction contribute to improve efficiency and narrow their efficiency gap with conventional n-i-p type devices. Our result suggests that the homojunction structure is an effective approach to reduce carrier recombination loss and achieve highly efficient PSCs. (C) 2022 Elsevier B.V. All rights reserved.
Dan, Nguyen HuyHau, Kieu XuanYen, Nguyen HaiThanh, Pham Thi...
7页
查看更多>>摘要：Alloy ribbons of Ni50-xCoxMn50-yAly (x = 5, 6, 7, 8 and 9; y = 18 and 19) were fabricated by using melt-spinning method. By varying Co and Al concentrations, the formation of crystalline phases, structural transformations and magnetic phase transitions can be tuned as desired. With high Al and Co concentrations, only a ferromagnetic-paramagnetic (FM-PM) transition of the austenitic phase occurs in the range of 350-450 K. While there is an additional weak ferromagnetic-ferromagnetic (WFM-FM) transition corre-sponding to the martensitic-austenitic (M-A) structural transformation for the ribbons with low Al and Co concentrations. The M-A transformation temperature of the alloy ribbons can be obtained in the range of 150-360 K. An anomalous change in structure and magnetic properties was observed in the ribbon sample with Co and Al concentrations of 8 and 18 at%, respectively. The external magnetic field has a pronounced effect on the M-A transformation and tends to shift this process towards lower temperatures. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：TiB2 nanoparticles were fabricated by the melt reaction between Al-10Ti and Al-3B master alloys. The reaction mechanism is ascribed to the decomposition of Al3Ti to release free Ti atoms, which diffuse across the AlB2/Al interface and substitute the Al atoms to form TiB2. This substitution produces a layer of pseudoTiB2 on the prism planes {10-10}AlB2 firstly, which has the same lattice structure and the similar values of the lattice parameter as AlB2. It follows the fact that the nucleation occurs at the prism planes {10-10}. Subsequently, the epitaxial transformation of TiB2 particles is initiated inward the pseudo-TiB2, which becomes detached from the substrate owing to the crystallographic mismatch between the two, thus forming the TiB2 nanoparticles. The exposed AlB2 prism surfaces continue to react with Ti atoms until they are totally consumed. Increasing the reaction temperature, prolonging the holding time could improve the extent of reaction, thus increasing the electrical conductivity and reducing the elastic modulus. Especially, the effects of ultrasonic vibration treatment (UVT) on the reaction process were explored. Cavitation and acoustic flow generated by UVT showed a magnificent potential for promoting the reaction in melts. Thanks to the interface reaction, nano-TiB2 particles can be generated. The nano-TiB2p/6201 composites produced by this method recorded significant improvement in the tensile properties.(c) 2022 Elsevier B.V.All rights reserved.
查看更多>>摘要：Rare-earth/alkaline-earth hexaborides with high chemical stability and low work function have recently attracted much interest as promising thermionic cathodes. Their synthesis at low temperatures without post-synthesis purification treatments is still a significant challenge. The present work demonstrates a simple synthesis technique to produce pure barium, cerium and gadolinium hexaborides (BaB6, CeB6, and GdB6). For each hexaboride, a batch of samples was created by first milling highly pure precursor powders and then firing at various temperatures in a low-vacuum furnace. The synthesised products were characterised using X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron dispersive spectroscopy (EDS). Their thermionic properties were investigated utilising a Schottky device. Pure BaB6, CeB6, and GdB6 were successfully synthesised at lower temperatures (<= 1400 degrees C). Nanocrystalline CeB6 was found to be produced at the lowest temperature of 1200 degrees C. The mean particle size of pure CeB6 and GdB6 synthesised is seen to be in the sub-micron range, with the exception of large BaB6 particles. The estimated work functions of the BaB6, CeB6, and GdB6 cathodes are 1.61 +/- 0.18 eV, 2.50 +/- 0.09 eV, and 2.42 +/- 0.09 eV, respectively. These findings imply that hexaborides, as promising thermionic emitters, can be easily produced at low temperatures. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Three-dimensional (3D) printing is considered to its the ability to make complex structures with modified properties in functional materials. In this work, a planar multi-layer anode-supported solid oxide fuel cell (SOFC) is fabricated through slurry-based 3D printing. The composition of 65 wt% NiO-YSZ (60:40 wt %)-35 wt% graphite is selected for fabrication of anode support by pressing. The low viscosity slurry with good homogeneity is prepared for fabricating of anode functional layer (AFL) consisting of NiO-YSZ (50-50), electrolyte (YSZ), and cathode (LSM) layers. After sintering of layers, uniform hierarchical porous microstructures are obtained with interconnected large pores up several microns and smaller pores of 100 nm in the AFL and cathode layer. In meanwhile, the electrolyte layer is achieved a relatively dense microstructure. The maximum power density at the output voltage of 0.5 V is achieved at 0.84 W/cm2 at an open-circuit voltage (OCV) of 1.06 V at 800 degrees C with H2 gas as fuel. The results are shown that the hierarchically macromesopores can create higher power density. Also, modification of geometry such as thickness and structure of layers can be improved electrochemical performance. Furthermore, the OCV exhibited a few fuel leakage due to the relatively dense structure and crack-free electrolyte layer. (c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：The present work examined the influence of anion type on incorporating WO3 into the MgO layer produced via plasma electrolytic oxidation of AZ31 Mg alloy. Here, three different anions, such as aluminate (AlO2-), silicate (SiO32-), and phosphate (PO43-) were added separately into an alkaline electrolyte containing WO3 nanoparticles. The microstructural observations revealed that the incorporation of the WO3 nanoparticles is affected by the diameter of discharge channels associated with the type of anion added into the electrolyte. The sample produced from phosphate electrolytes had higher thickness but was more porous than those obtained in aluminate or silicate electrolytes. Regardless of anion type, the amounts of WO3 nanoparticles incorporated into the inner layer of PEO coating were more significant than those incorporated into the outer layer, where a WO3-rich inner layer was obtained in the case sample coated in electrolyte with silicate anions. The electrochemical measurements in a 3.5 wt% NaCl solution indicated that the corrosion resistance of the sample coated in silicate electrolyte was superior to other samples in which the sample coated in phosphate electrolyte exhibited the lowest corrosion resistance. This behavior is explained by a mechanism in which every anion produces its microstructural defects under the influence of discharge types, such as type-A, B, C, D, and E, thus, affecting the physical incorporation of WO3 into the MgO layer under plasma conditions. (c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：The effects of fibrous Cr phase on the adiabatic shearing anisotropic behavior of the Cu-15Cr in-situ composite model alloy were firstly studied by a split Hopkinson pressure bar (SHPB), Optical Microscope (OM), and X-ray diffraction (XRD) technique. Specimens were loaded along the rolling direction (Cu-15Cr0 degrees) and perpendicular to the rolling direction (Cu-15Cr-90 degrees). The experimental and analysis results showed that there were differences in the number of phase interfaces and phase interface distance that the shear stress crossed when sheared along with different directions due to the directional arrangement of the fibrous Cr phases, which caused the strain hardening, strain rate hardening and thermal softening of the Cu15Cr in-situ composite were anisotropic. The Cu-15Cr-90 degrees specimen possessed lower strain rate hardening and higher thermal softening at the same strain rate, and the strain hardening rate was similar to that of the Cu-15Cr-0 degrees specimen as the shearing process proceeded, so the Cu-15Cr-90 degrees specimen was more prone to adiabatic shearing than the Cu-15Cr-0 degrees specimen. In addition, a splitting crack was produced at the Cr phase and matrix interface in the Cu-15Cr-0 degrees specimen due to the additional tensile stress produced in the Cr phase during shearing. The perpendicular Cr phase in the Cu-15Cr-90 degrees specimen was deflected parallel to the shear stress during shearing, so it was not easy to produce splitting cracks. However, the tip of the Cr phase without deflection was more likely to possess high additional tensile stress, so the crack in the Cu15Cr-90 degrees specimen was extended along the edge of the adiabatic shear region at the tip of the Cr phase. (c) 2022 Elsevier B.V. All rights reserved.
NSTL
Elsevier