Study of Phase Composition of a Siilcon Nitride (Si3N4)-Rare-Earth Oxide Ceramic Sintered under High Pressures
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摘要: 在5~7 GPa，600~1 800 ℃的压力-温度范围内对组份为氧化硅-稀土氧化物微粉混合物（3-Si3N4+0.5La2O3+0.5Pr6O11（mol.%））的烧结产物进行了研究。所得结果表明其成相规律与Sialon体系在高温高压下烧结时不同。在直到5 GPa的高压下，-Si3N4表现出相当高的稳定性，并不转变成相。当烧结温度低于1 600 ℃时，烧结体仍然由以-Si3N4为基础的固溶体及稀土氧化物组成，而后者则表现出一系列相变化。当压力超过6 GPa、温度高于1 600 ℃时，物料烧结成一个新的单相高压结构ReSi3O2N4。其衍射数据可以用一个正交点阵来拟合。其晶格参数为：a=1.298 3 nm，b=0.814 0 nm，c=0.428 5 nm。Abstract: The phase compositions of silicon nitride-rare-earth oxide ceramic (3-Si3N4+0.5La2O3+0.5Pr6O11 (mol.%)) sintered in a pressure range from 5 to 7 GPa, temperature from 600 ℃ to 1 800 ℃ has been studied by X-ray diffraction and SEM observation. The observed results show that the phase forming rule at high p-T is different from that of Si3N4-Al2O3-AlN system. Under high pressure and below 1 600 ℃, the sintering products are mixture of Si3N4 and the polymorphs of the rare-earth oxides. Si3N4 remains -structure even when certain amount of rare earth oxides has dissolved in. when the temperature exceeds 1 600 ℃ and pressure is above 6 GPa, a new single phase belonging to orthorhombic system is formed with lattice parameters a=1.298 3 nm, b=0.814 0 nm, c=0.428 5 nm.
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