Transparent alumina ceramic with complicated shape prepared by slip casting

Abstract

Development of transparent property of polycrystalline alumina ceramic was proposed this research work. Fabrication of full density specimen and control of grain size within submicron order was mainly focused. Commercial alumina nanopowder was employed as a raw material in this work. Various specimens were molded by slip casting method. The objectives of this research were to investigate the effect of addition of binder into alumina slurry for slip casting and that of sintering parameters to obtain the full density and submicron grain. The experimental results show that the optimal PVA binder for slip casting should not exceed 0.2 wt% with 75 wt% alumina content. This well dispersed alumina composition could provide the circular pellet and alphabet- shaped alumina specimens without breakage by slip casting. As a result, the specimens with the relative density up to 58% could be prepared. In the sintering process, types of furnace, sintering temperature and soaking time in pre-sintering were important factors to gain the fully dense alumina specimens. It was found that the grain growth mechanism immediately occurred after densification in sintering process. Moreover, the two-step sintering proposed as an alternative pre-sintering was employed to get the full density and suppress the grain growth. After pre-sintering, the specimens were subject to the post-sintering by a hot isostatic pressing (HIP) furnace to eliminate the residual closed pores. The HIPed specimens could exhibit transparent property owing to the controlled grain size at submicron level. Both of circular pellet and alphabet-shaped specimens have a high transparency after being HIPed.