Vacuum Sintering of Zirconia Based Ceramics

Abstract

Plasma spray pyrolysis method for fabricating ceramics is growing in attention from scientific and technological points of view [1,2]. This method seems to be a suitable one for the preparation of ultrafine powders of the multicomponent oxide systems in which each component is uniformly distributed. Although these unique spray pyrolysis zirconia-base powders have been synthesized, only few investigators have been reported dealing with the fabrication of specimens from the dense, high-strength ceramics. It may be due to the major disadvantage of the spray pyrolysis powders. As a rule, they consist from the hollow spheres and irregularly-shaped particles [1,3]. To improve the sinterability of highly agglomerated ceramic powders, various approaches such as mechanical milling of powders [4] as well as adding of various dopant, [5] have been reported in the literature. However, these methods often reveal themselves to be too tedious processes. The increase of the sintering temperature with the purpose to intensify diffusion processes is technically easier to do, however this may used not for all materials. For example, optimum sintering temperatures for conventionally fabricated Y-TZP at which the densification will be reasonably rapid, but where the abnormal grain growth will not occur are less 1600 °C [6]. At temperatures above 1600°C the increasing grain size exceeds the critical grain size for spontaneous tetragonal-to-monoclinic transformation in the sample and leads to the cracking which accompany the transformation reduces the overall density.