Sintering Mechanism of Fine Zirconia Powders with Alumina Added by Various Ways

摘要

Small amounts of Al_2O_3 were added to fine zirconia powder by different ways: powder mixing, hydrolysis of alkoxide, and homogeneous precipitation. During a constant rate heating process, the Al_2O_3 addition slightly raised the starting temperature of densification of powder compact, and the densification was remarkably stimulated by Al_2O_3 at temperatures above about 1100°C. According to an isothermal analysis of densification, the densification rate was retarded by Al_2O_3 addition just after the start of sintering and then the densification rate increased significantly during sintering compared to Al_2O_3-free powder. These results mean that Al_2O_3 particles pinned the shrinkage of zirconia powder compact at the initial stage, and diffuse toward zirconia surface to enhance the sintering. The sintering mechanism was explained by the grain-boundary diffusion for the Al_2O_3-free powder and the volume diffusion for Al_2O_3-added powder. When the Al_2O_3 was added to zirconia powder by homogeneous precipitation and alkoxide methods, the densification rate was more stimulated compared to powder mixing method. The sintering mechanism did not change by the way for Al_2O_3 addition. The Al_2O_3 addition by the chemical process tended to enhance the grain growth of zirconia, while the uniform microstructure was achieved because of homogeneous addition of Al_2O_3 by these chemical processes.