Sintering Behavior of Ultrafine Alumina Powders Prepared by CVD-Method

Abstract

The sintering of CVD-alumina powders (I: average particle size 0.03μm, mixture of γ-and δ-phases; II: average particle size 0.16μm, mixture of δ-and ι-phases) was investigated in argon atmosphere at 1100°-1600°C. The sinterability of (I) increased remarkably with the phase transition into α-phase by the calcination at 1300°C, although the particle size increased to 0.14μm. Such an increase in sinterability was attributed to the increase in green density of the powder compact. The relative density of the sintered body obtained was 96% by 1500°C-sintering. On the other hand, the phase transition in powder (II) was slow in 1300°C-calcination and the sinterability was lower than that of powder (I), probably due to the low density of powder compact in addition to the large particle size. A denser powder compact obtained by rubber-pressing gave the denser sintered body, supporting the significant effect of the green density on the densification, The high green density was also effective for the suppression of grain growth, which may be due to the homogenization in particle packing. The heating schedule was also important to obtain a homogeneous microstructure.