不同烧结助剂制备的Si_3N_4陶瓷的氧化行为

以α-Si3N4粉末为原料,分别以Y2O3-La2O3和Y2O3-CeO2为烧结助剂,利用热压烧结法制备了Si3N4陶瓷。研究了Si3N4陶瓷样品在空气中高温下的氧化行为。结果表明:原始的α-Si3N4在烧结过程中完全转化为β-Si3N4。在1000～1350℃氧化100h后,用Y2O3-La2O3烧结助剂制备的样品表现为质量增加趋势,质量变化小于0.389mg/cm2,其氧化过程符合抛物线规律。用Y2O3-CeO2烧结助剂制备的样品,在1000℃氧化后表现为质量减小,为-0.248mg/cm2;在1230℃和1350℃表现为质量增加,分别为0.024mg/cm2和0.219mg/cm2,并且其氧化过程不符合抛物线规律。样品的氧化过程主要受2个扩散过程的控制,即稀土元素的向外扩散与氧的向内扩散。

OXIDATION BEHAVIOR OF Si3N4 PREPARED WITH DIFFERENT SINTERING ADDITIVES

Si3N4 ceramics were sintered by hot pressing using α-Si3N4 as raw materials and Y2O3-La2O3 or Y2O3-CeO2 as sintering additives. The oxidation behavior of ceramics in air at high temperature was investigated. The results show that α-Si3N4 converts into β-Si3N4 completely after sintering. The mass of Si3N4 ceramic prepared using Y2O3-La2O3 as sintering additive increases after oxidi-zation at 1 000-1 350 ℃ for 100 h,its mass gain is lower than 0.389 mg/cm2,and the oxidization process satisfies the parabolic law. For the Si3N4 ceramic prepared using Y2O3-CeO2 sintering additive,however,its mass decreases after oxidation at 1 000 ℃ for 100 h,reaching -0.248 mg/cm2. The mass of the ceramic increases after oxidation at 1 230 and 1 350 ℃ for 100 h. Its mass gain are 0.024 and 0.219 mg/cm2,respectively,and its oxidization process did not satisfy the parabolic law. The oxidation process contains two diffusive mechanisms：the outward diffusion of the rare earth elements and the inward diffusion of oxygen.