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Eutectic compositions of Al2O3 and ZrO2 have been melted and rapidly solidified by shock-wave quenching, flame-pressure atomization and high-pressure water atomization. Quenching rates > 104 K/s resulted in amorphous particles which, on annealing, crystallized at 1310°C. Microcrystalline particles with tetragonal ZrO2 distributed in an ?-Al2O3 matrix formed at lower quenching rates. ?-Al2O3 transformed into α-Al2O3 on annealing at 953°C. 相似文献
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A data set was established to calculate the phase equilibria in the systems Si-Al-Zr-O-N and Si-Al-B-O-N. Complete phase diagrams of the quasibinary and quasiternary boundary systems, calculated by this data set, agree well with literature phase diagrams. To calculate equilibria of the multicomponent systems, Eriksson's program was modified to accept ionic species. The equilibria of some concentrations are plotted versus the temperature in phase amount diagrams. 相似文献
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The chemical stability of perovskites LaBO3 where B = V, Cr, Mn, Fe, Co, Ni was studied by thermogravimetry at 1000°C in gas mixtures of , and at 1 bar.The stability limits of the perovskite phases expressed in terms of -log Po2★ (Po2★ = critical oxygen partial pressure in bar) were for LaCrO3 and LaVO3 (greater than 21.1), LaFeO3 (16.95), LaMnO3 (15.05), LaCoO3 (7.0) and for LaNiO3 (~0.6). The changes in standard enthalpy ΔH° and entropy ΔS° of the following reactions were obtained., 相似文献
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J. Weiss L. J. Gauckler H. L. Lukas G. Petzow T. Y. Tien 《Journal of Materials Science》1981,16(11):2997-3005
The phase relations in the system Si-Al-Zr/N-O are studied by experiment and by thermodynamic calculations. The results show the conditions under which such ceramics can exist and thereby explain contradictions between earlier results. The knowledge of these phase equilibria makes it possible to choose suitable material compositions in order to apply the toughening effects of ZrO2 on a SiAlON matrix. 相似文献
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A newly set up computer program based on the mathematical principles suggested by M. Hillert was used to calculate the phase equilibria in the system CSiN0. These calculations include phase equilibria with the vapour phase. Several isothermic and T-c-sections of the ternary boundary systems and of the quaternary system are given. 相似文献
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Niobium and tantalum surfaces easily absorb oxygen. With decreasing particle size the content of oxygen increases. The role
of this surface oxygen and oxygen in the sintering atmospheres on the first-stage sintering is not well established. Therefore
the sintering behavior of high-purity niobium powders was studied by annealing cylindrical powder compacts (particle size
<63 μm) in the temperature range from 1000°C to 1600°C in ultra-high vacuum and under low oxygen partial pressures, as well
as in inert gas atrnospheres with low oxygen contents. The specific surface of the samples was determined by metallographic
methods, adsorption, and capacitance measurements. Low oxygen partial pressures (10-3 Pa) lead to a slight enhancement of the surface diffusion which is controlling first-stage sintering. High heating rates
(0T > 3000 min-1) to temperatures above the melting point of Nb2O5 (Tm = 1495 °C) enhances the neck growth due to the formation of a liquid oxide phase on the surface of the powder particles.
This paper is based on a presentation delivered at the symposium “Activated and Liquid Phase Sintering of Refractory Metals
and Their Compounds” held at the annual meeting of the AIME in Atlanta, Georgia on March 9, 1983, under the sponsorship of
the TMS Refractory Metals Committee of AIME 相似文献