稀土掺杂对γ-Al_2O_3相变及烧结行为的影响

Effect of Rare Earth Dopant on Phase Transformation and Sintering Behavior of γ-Al_2O_3

研究了稀土氧化物CeO2、La2O3掺杂对γ-Al2O3烧结行为的影响。结果表明各样品的相变起始温度基本一致,但掺杂样品的相变结束温度和最大相变速率对应温度均较纯样品有所升高(La2O3掺杂样品相变结束温度和最大相变速率对应温度分别升高了48℃和27℃)。同时发现La2O3掺杂样品的最终线收缩率小于CeO2掺杂样品,主要是由于La3+离子半径大于Ce4+,其在晶界处的偏聚浓度高于Ce4+,因此对晶界迁移阻碍作用较大。SEM观察表明,相对于纯样品,掺杂样品颗粒细化,密度降低,这主要归结于掺杂稀土在氧化铝晶界上的偏聚阻碍了烧结过程中的物质迁移。

The effect of rare earth oxide （cerium and lanthanum oxide） on the phase alumina ceramics was investigated. The samples were sintered pressurelessly sintering behavior of γ at constant heating rate of 5 ℃/min. The results show that the initial temperatures corresponding to the γ→α for rare earth oxide doped and pure T-Al2O3 samples are similar; however, the temperatures corresponding to the maximum phase transformation rate and phase transformation termination of doped alumina ceramics are higher than that of pure T-Al2O3 （ the temperatures of La2O3 doped sample are higher than that of the pure sample by 27 ℃ and 48 ℃, respectively）. In addition, it is found that the final linear shrinkage of La2O3 doped sample is smaller than that of CeO2 doped sample. Compared with Ce^4＋ , the concentration of La^3＋ with larger ionic radius at the grain boundary is much higher, which makes the mass transportation difficult for La2O3 doped sample during the sintering process. For sintered samples, morphology of fracture is characterized by SEM. It is found that the grain size of rare earth doped samples is smaller than that of pure Al2O3 sample. It can be attributed to the strong segregation of rare earth cations at grain boundaries, which will reduce both the grain growth kinetics and phase transformation rate for a given temperature.