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1.
Han Chen Shunzo Shimai Jin Zhao Xiaojian Mao Jian Zhang Guohong Zhou Shiwei Wang 《Journal of the European Ceramic Society》2021,41(6):3838-3843
Alumina platelets were arranged horizontally in submicron alumina particles by shear force in the flow of slurries during casting. The obtained alumina green bodies with platelets were pressureless-sintered in vacuum, producing ceramics with thoroughly oriented grains and high transmittance. The effects of sintering parameters on the densification, microstructure evolution, and orientation degree of alumina ceramics were investigated and discussed. The results showed that the densification, grain size, orientation degree, and in-line transmittance were increased with increasing sintering temperature. The enhancement of orientation degree was mainly coherent with grain growth. The grain-oriented samples exhibited a much higher in-line transmittance (at 600 nm) of 61 % than that of the grain random sample (29 %). Moreover, the transmission remained a high level in the ultraviolet range (<300 nm). 相似文献
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《Journal of the European Ceramic Society》2020,40(6):2268-2278
Pure h-BN ceramic specimens were prepared by hot-pressing under different sintering temperatures and pressures using ball milled h-BN powders composed of amorphous and nanocrystalline BN. Microstructures and thermal conductivities of these h-BN ceramic specimens were characterized and measured. Higher sintering pressure is more favorable to the preferred orientation growth of plate-like h-BN grains along the pressure direction, forming microstructures where the c-axes of h-BN grains are preferentially oriented perpendicular to the pressure direction. However, such microstructures can only be obtained at appropriate sintering temperature. Thermal conductivities of h-BN ceramic specimens are strongly related to their microstructures, especially the grain orientation. Growth mechanisms of h-BN grains were investigated. There is multi-area co-growth phenomenon around the grain boundaries composed of the basal planes of h-BN grains, which results in the formation of stacking faults in the as-grown h-BN grains. 相似文献
3.
This work proposes a scheduling problem for the workforce management in a chain of supermarkets operating in Italy. We focus on determining the ideal mix of full-time and part-time workers which are needed every week to guarantee a satisfactory service level during the check-out operations. The generation of working shifts, to be assigned to retail workers, is subject to several constraints imposed by both labour laws and enterprise bargaining agreements.We present a mathematical formulation of the problem followed by an exact solution approach which relies on the definition of feasible daily working shifts. The number of feasible daily shifts, that are combined to determine feasible weekly shifts, could drastically increase, depending on the selected planning interval. In addition, there may exist additional constraints, that are difficult to incorporate into the mathematical model. For these reasons, a hybrid heuristic, which does not require the generation of all feasible weekly shifts, is proposed in this paper.Using appropriate statistical techniques, a sensitivity analysis is performed to test the design of the hybrid heuristic. Computational tests are carried out by solving several real instances provided by the retail firm. The results obtained by the heuristic are compared both with an exact approach and with the solutions adopted by the retail company, which have been determined by using a naïf approach. Our hybrid heuristic exhibits excellent performance finding optimal or near optimal solutions in a very limited CPU time. 相似文献
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We fabricated Sr and Ca-doped CuAlO2 compacts from the mixed powder of CuO, Cu2O, Al2O3, and SrO or CaO by multi-pass hot pressing followed by spark plasma sintering (SPS). The XRD results showed the reaction of CuO, Cu2O and Al2O3 was rather complete and only CuAlO2 single phase was formed when the additive amount of SrO or CaO was appropriate. Multi-pass hot pressing increased the relative density and the usage of plate-like Al2O3 as reaction raw material enhanced the orientation degree. In spite of performance improvement conflicts through elemental doping, density increase and orientation improvement, the measurement on the thermoelectric performance indicated that the electrical resistivity, Seebeck coefficient, power factor, dimensionless figure of merit (ZT) were improved to varying degrees through the synergetic action of elemental doping, density increase, and orientation control. The highest power factor and ZT of the Ca-doped CuAlO2 compacts reached 1.54?×?10?4 W?m?1 K?2 and 0.015 at 973?K, respectively. The thermoelectric performance was higher than those of CuAlO2 at the same temperature in published work before. 相似文献
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An α/β two-phase Ti-6 Al-4 V alloy was fabricated by electron beam melting to obtain a basketweave structure.The orientation dependence of the mechanical properties of Ti-6 Al-4 V alloy was studied by micro-pillar compression and post-mortem transmission electron microscopy analysis.The results indicate that different grains have different mechanical responses,and the possible attributions were discussed.Besides the orientation effect,due to the limited volumes of micropillars,the size of the a phases,dispersion of the β phases,and the presence of the free dislocation path also affect the mechanical properties of the micropillars to a large extent.Although no direct link was discovered between the mechanical properties and the parent βorientations,this work provided a promising method to further study the anisotropic mechanical behavior in Ti-6 Al-4 V alloy. 相似文献
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