Sintering mechanism of fine zirconia powders with alumina added by powder mixing and chemical processes

The present study examined the sintering behavior of fine zirconia powders (containing 2.9 mol% Y2O3) with and without small amounts of Al2O3 added by different ways: powder mixing (PM), homogeneous precipitation (HP), and hydrolysis of alkoxide (HA). The initial sintering behavior was examined by both measurement methods of a constant rate of heating and isothermal shrinkage. In the PM process, Al2O3 particles pinned the shrinkage of zirconia powder compact at the initial stage and diffuse toward zirconia surface to enhance the sintering. This initial sintering mechanism was explained by the grain-boundary diffusion for the Al2O3-free powder and the volume diffusion for Al2O3-added powder. When Al2O3 was added to zirconia powder by HP and HA processes, the densification rate was more stimulated compared to the PM process. The initial sintering mechanism did not change by the way for Al2O3 addition. The Al2O3 addition by chemical processes of HP and HA tended to enhance the grain growth of zirconia, while the uniform microstructure was achieved because of homogeneous addition of Al2O3 by those processes.