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[en] Silicon carbide was synthesized by reaction sintering process from carbon and silicon powders as starting materials. The effects of two processing parameters, i.e., heat treatment time and temperature, were examined (to characterize the reaction sintering process) in terms of the degree of reaction and phase developed during heat treatment. The final products after reaction of silicon and carbon powders were identified as β-SiC having ZnS crystal structure. Sintering of cordierite ceramics which was used as an high temperature inorganic binder to fabricate ceramically bound silicon carbide, and phase identification of the sintered ceramics by X-ray powder diffraction techniques. (Author)
[en] We report the Sr and Ba isotopic compositions of 18 presolar SiC grains of types Y (11) and Z (7), rare types commonly argued to have formed in lower-than-solar metallicity asymptotic giant branch (AGB) stars. We find that the Y and Z grains show higher Sr/Sr and more variable Ba/Ba ratios than mainstream (MS) grains. According to FRANEC Torino AGB models, the Si, Sr, and Ba isotopic compositions of our Y and Z grains can be consistently explained if the grains came from low-mass AGB stars with 0.15 Z ≤ Z < 1.00 Z, in which the C neutron exposure for the slow neutron-capture process is greatly reduced with respect to that required by MS grains for a 1.0 Z AGB star. This scenario is in line with the previous finding based on Ti isotopes, but it fails to explain the indistinguishable Mo isotopic compositions of MS, Y, and Z grains.
[en] Highlights: • SiOC microstructure is influenced by the solvent trapped in the precursors. • Solvent influences carbon content and crystallization of SiC during pyrolysis. • Accelerated SiC formation is more prominent at lower pyrolysis temperature. • SiC formation decreases with solvent content at higher pyrolysis temperature.
[en] An optically controlled SiC/SiCGe lateral power transistor based on superjunction structure has been proposed, in which n-SiCGe/p-SiC superjunction structure is employed to improve device figure of merit. Performance of the novel optically controlled power transistor was simulated using Silvaco Atlas tools, which has shown that the device has a very good response to the visible light and the near infrared light. The optoelectronic responsivities of the device at 0.5 μm and 0.7 μm are 330 mA/W and 76.2 mA/W at 2 V based voltage, respectively. (semiconductor devices)
[en] Optical switch-on of a high-voltage (12 kV class) 4H-SiC thyristor to a current I = 100 A is reported. The importance of the dI/dt ramp and the turn-on spread for obtaining the maximum switched-on current Imax is discussed. It is demonstrated that Imax can be substantially raised by using a mixed resistive–inductive load. (paper)
[en] In this study, SiC reinforced aluminum (Al) metal matrix composites were prepared by microwave sintering. The effects of SiC content, pressure and sintering temperature on the density, hardness and microstructure of the composites were investigated. It was found that the relative density of SiC/Al composites is 98.43% when the content of SiC is 5 Vol%. When the SiC content is 15 vol%, the sintering temperature is 770 °C and the pressure is 250 MPa, the density and hardness of the composites SiC/Al composites are 96.14% and 130 HV, respectively. And the SiC particles can be uniformly dispersed in the Al matrix by microwave sintering. (paper)
[en] Presolar silicon carbide (SiC) grains in meteoritic samples can help constrain circumstellar condensation processes and conditions in C-rich stars and core-collapse supernovae (CCSNe). This study presents our findings on eight presolar SiC grains from asymptotic giant branch (AGB) stars (four mainstream and one Y grain) and CCSNe (three X grains), chosen on the basis of μ-Raman spectral features that were indicative of their having unusual non-3C polytypes and/or high degrees of crystal disorder. Analytical transmission electron microscopy (TEM), which provides elemental compositional and structural information, shows evidence for complex histories for the grains. Our TEM results confirm the presence of non-3C,2H crystal domains. Minor-element heterogeneities and/or subgrains were observed in all grains analyzed for their compositions. The C/O ratios inferred for the parent stars varied from 0.98 to ≥1.03. Our data show that SiC condensation can occur under a wide range of conditions, in which environmental factors other than temperature (e.g., pressure, gas composition, heterogeneous nucleation on precondensed phases) play a significant role. Based on previous μ-Raman studies, ∼10% of SiC grains may have infrared (IR) spectral features that are influenced by crystal defects, porosity, and/or subgrains. Future sub-diffraction-limited IR measurements of complex SiC grains might shed further light on the relative contributions of each of these features to the shape and position of the characteristic IR 11 μm SiC feature and thus improve the interpretation of IR spectra of AGB stars like those that produced the presolar SiC grains.
[en] Relationship between critical charge density, holding current, and maximum current density has been studied by using an adequate numerical model for the axisymmetric configuration characteristic of the optical triggering of power silicon carbide thyristors. It is shown that the holding current Ih depends only weakly on the critical charge density of a thyristor, pc. At the same time, the maximum current density in the state corresponding to holding current grows very steeply with increasing pc. It is shown that the maximum current density can substantially increase with decreasing current in the axisymmetric configuration if the switched-on state occupies only a part of the total area of a thyristor. (paper)