氮化硅(Si_3N_4)-稀土氧化物陶瓷的超高压烧结研究

STUDY OF PHASE COMPOSITION OF A SILICON NITRIDE(Si_3N_4)-RARE-EARTH OXIDE CERAMIC SINTERED UNDER HIGH PRESSURES

在5～7GPa,600～1800℃的压力-温度范围内对组份为氮化硅-稀土氧化物微粉混合体(3Si_3N,+0.5La_2O_3+0.5Pr_6O_(11)(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5GPa的高压力下,α-Si_3N_4表现出相当高的稳定性,并不转变成β相。当烧结温度低于1600℃时,烧结体仍然由以α-Si_3N_4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6GPa、温度高于1600℃时,物料烧结成一个新的单相高压结构ReSi_3O_2N_4。其衍射数据可以用一个正交点阵来拟合。其晶格参数为:α=1.2983nm,b=0.8140nm,c=0.4285nm。

The phase compositions of silicon nitride-rare-earth oxide ceramic (3Si3N4 +0.5La2O3+0. 5Pr6O11(mol. %) sintered in a pressure range from 5 to 7GPa, temperature from 600℃ to 1800℃ 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 1600℃ ,the sintering products are mixture of Si3N4 and the polymorphs of the rare-earth oxides. Si3N4 remains α-structure even when certain amount of rare-earth oxides has dissolved in. When the temperature exceeds 1600℃ and pressure is above 6GPa, a new single phase belonging to orthorhombic system is formed with lattice parameters a =1. 2983nm,6=0. 8140nm,c=0. 4285nm.