Mechanism of Alumina-Enhanced Sintering of Fine Zirconia Powder: Influence of Alumina Concentration on the Initial Stage Sintering

The isothermal shrinkage behavior of 2.9 mol% Y2O3-doped ZrO2 powders with 0–1 mass% Al2O3 was investigated to clarify the effect of Al2O3 concentration on the initial sintering stage. The shrinkage of the powder compact was measured at constant temperatures in the range of 950°–1050°C. The Al2O3 addition increased the densification rate with increasing temperature. The values of apparent activation energy (nQ) and apparent frequency-factor term (β0n), where n is the order depending on the diffusion mechanism, were estimated at the initial sintering stage by applying a sintering-rate equation to the isothermal shrinkage data. The diffusion mechanism changed from grain-boundary diffusion (GBD) to volume diffusion (VD) by Al2O3 addition and both nQ and β0n increased with increasing Al2O3 concentration. The kinetic analysis of the sintering mechanism suggested that the increase of densification rate by Al2O3 addition largely depends on the increase of β0n, that is, the increases of n with GBD→VD change and β0 with an increase in Al2O3 content, although the nQ also increases with Al2O3 addition. This enhanced sintering mechanism is reasonably interpreted by the segregated dissolution of Al2O3 at ZrO2 grain boundaries.