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111.
Joining of Ti-coated monolithic SiC using a SiCw/Ti3SiC2 filler by electric field-assisted sintering
Teng Yu Heejin Kwon Linkun Shi Xiaobing Zhou Dang-Hyok Yoon Peter Tatarko Xin Xu Zhengren Huang Qing Huang 《Journal of the European Ceramic Society》2021,41(3):1834-1840
Monolithic SiC, for the first time, was successfully joined using a SiC whisker-reinforced Ti3SiC2 composite (SiCw/Ti3SiC2) filler via electric field-assisted sintering technique. A thin Ti coating layer was formed on the SiC surface to minimize the residual stress at the joint interface by transforming it into a TiC gradient layer. After optimizing process parameters, a joint strength higher than 250 MPa was obtained, which is higher than the other values reported in the literature. Failure occurred at the SiC base rather than the joining interface because of the improved joint strength by the incorporation of SiCw. The addition up to 15 wt. % SiCw in the filler layer improved the joint strength by various strengthening mechanisms. On the other hand, the joint strength was lower with 20 wt. % SiCw addition, indicating the importance of thermal expansion mismatch between SiCw and Ti3SiC2 to obtain a sound SiC joint. 相似文献
112.
《Journal of the European Ceramic Society》2022,42(12):4980-4986
Titanium oxide is a promising thermoelectric material because of its high stability and low cost. We synthesize novel titanium-niobium-oxygen composite ceramics directly from elementary substance Nb and TiO2 under high-pressure and high-temperature (HPHT) in this work. Elemental substance Nb will reduce TiO2 to Magnèli phase titanium oxide at high pressure and high temperature. In this process, elemental substance Nb is oxidized to various niobium oxides. The experimental results show that the composite ceramics have a special 'pore' microstructure, and their thermoelectric and mechanical properties are very prominent among metal oxide thermoelectric materials. After repeated tests, the optimum concentration sample zT value is 0.313 at 973 k, with a Vickers hardness of 7.06. This work provides a novel concept for improving the performance of TiO2 by reducing it with metal elementary substances other than Ti. 相似文献
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115.
《Ceramics International》2019,45(12):15097-15107
Blending different cathode materials to construct composites can be in compatibility with their individual advantages to exhibit better electrochemical performances. In this study, we blend Li-rich and classical layered cathode materials to realize the suppression of voltage decay. The electrochemical results indicate that the composite electrodes show better capacity retention exceeding 90% after 100 cycles. More importantly, the cumulative voltage decay of the composite materials with different ratio are 280 mV and 140 mV for 100 cycles’ duration, which are much lower than that of the single component with 390 mV in Li-rich layered cathode, respectively. Based on the ex situ X-ray diffraction, the blended composites show the structural origin of synergy effect, which are like a pair of parallel resistors to reciprocally buffer the crystal structure change during the charge and discharge process between Li-rich and classical layered cathode materials. Blending of layered cathode oxide materials with the synergy effect provide a possible approach to achieve more excellent electrochemical performances in lithium-ion batteries. 相似文献
116.
《International Journal of Hydrogen Energy》2019,44(31):16824-16832
High-energy density and low cost magnesium nanoparticles (Mg NPs)-based material are being sought to meet increasing capable of hydrogen (H2) storage demand. Here, a kind of air-stable Mg NPs supported on porous structured multi-walled carbon tubes-polymethyl methacrylate (MWCNTs-PMMA) template is prepared owing to reversible well-distributed, dispersed and small-sized Mg/MgH2 NPs. The aim is to improve the H2 storage capacity, hydrogen sorption kinetics and thermodynamics of nano Mg-based system without using catalyst. The organic Mg precursor was directly in-situ reduced to metallic Mg NPs in MWCNTs-PMMA template by lithium naphthalide. The size distribution of reduced Mg nanoparticles is around 3.6 ± 0.2 nm, confirmed by XRD and TEM analyses, which is due to the strong interaction between Mg NPs and MWCNTs-PMMA via PMMA binding Mg2+, as well as the confinement of porous template hindered the growth and agglomeration of Mg NPs. Moreover, except H2, O2 and H2O molecules can't infiltrate the porous structure of MWCNTs-PMMA resulted in the presence of air stable Mg NPs in the MWCNTs-PMMA. The work provides a new scope to prepare nano metal-based composite for H2 storage. 相似文献
117.
《Diamond and Related Materials》2005,14(1):16-22
A bulk sample of nanocrystalline cubic diamond with crystallite sizes of 5–12 nm was synthesised from fullerene C60 at 20(1) GPa and 2000 °C using a multi-anvil apparatus. The new material is at least as hard as single crystal diamond. It was found that nanocrystalline diamond at high temperature and ambient pressure kinetically is more stable with respect to graphitisation than usual diamonds. 相似文献
118.
A detailed calculation of lattice thermal conductivity of freestanding Wurtzite GaN nanowires with diameter ranging from 97 to 160 nm in the temperature range 2–300 K, was performed using a modified Callaway model. Both longitudinal and transverse modes are taken into account explicitly in the model. A method is used to calculate the Debye and phonon group velocities for different nanowire diameters from their related melting points. Effect of Gruneisen parameter, surface roughness, and dislocations as structure dependent parameters are successfully used to correlate the calculated values of lattice thermal conductivity to that of the experimentally measured curves. It was observed that Gruneisen parameter will decrease with decreasing nanowire diameters. Scattering of phonons is assumed to be by nanowire boundaries, imperfections, dislocations, electrons, and other phonons via both normal and Umklapp processes. Phonon confinement and size effects as well as the role of dislocation in limiting thermal conductivity are investigated. At high temperatures and for dislocation densities greater than 1014 m?2 the lattice thermal conductivity would be limited by dislocation density, but for dislocation densities less than 1014 m?2, lattice thermal conductivity would be independent of that. 相似文献
119.
《Journal of the European Ceramic Society》2021,41(15):7601-7609
The response of C/SiC composites prepared via precursor impregnation and pyrolysis was investigated in a 1 MW plasma wind tunnel. Under a considerable aero heating of up to 26.2 MJ/kg of specific total enthalpy, the samples were exposed to heat fluxes exceeding 5.7 MW/m2 and low pressures of 4.5–6.6 kPa. The samples were able to withstand low heat fluxes and low stagnation pressures, and their carbon-rich nature improved the thermal conductivity, presenting a low steadystate surface temperature. However, a spontaneous jump in the surface temperature at around 1700 °C was observed at high heat fluxes and high stagnation pressures. The jump temperature was lower compared with that reported in previous studies, and was found to increase rapidly to temperatures above 2000 °C. This low-temperature jump phenomenon was associated with the evolution of microstructure during testing, and the underlying mechanism was revealed through the use of thermodynamics analysis. 相似文献
120.
《International Journal of Hydrogen Energy》2019,44(5):3195-3207
This paper presents three-dimensional direct numerical simulations of lean premixed H2/air flames with equivalence ratios 0.4, 0.5 and 0.6, respectively. The initial Karlovitz number is around 2335 and the pressure is 20 atm, which is relevant to gas turbine conditions. The heat release in reaction zones under different equivalence ratios is examined statistically with the aim to extend our understanding of lean combustion under high-pressure conditions. With increasing equivalence ratio, the relative thickness of reaction zone (δf/δL) is increasing for both laminar and turbulent flames, but the extent of increase is reduced under high equivalence ratio. By examining the local structures of flame fronts, it is found that trenches and plateaus of local equivalence ratio are located on separate sides of the reaction zone edge. Due to the decreased Lewis number under high equivalence ratio, the trench ‘depth’ and plateau ‘height’ are reduced. For the flame under ultra-lean conditions, there are some spots with temperatures above adiabatic temperature. This is attributed to the high-fraction of radicals in these regions, which will promote heat release. Furthermore, the heat release rates of elementary reactions are investigated with the analysis of radical fractions and rate constants. When the mixture equivalence ratio varies, the local heat release is changed in different temperature windows due to the combined effects of radical fractions and reaction rate constants. 相似文献