Fumed oxides as base materials for ceramic applications

Abstract

Highly dispersed zirconium oxide in the tetragonal modification is obtained by high-temperature hydrolysis of gaseous zirconium tetrachloride. Variation of the reaction parameters allows the control of the powder properties over a wide range. In order to facilitate handling, the very fluffy oxides were densified by calcining or spray drying of aqueous slurries. After spray drying, in contrast to calcining, neither a transformation of the tetragonal phase into the monoclinic form nor a decrease of the surface area was observed. Yttria-doped zirconias were produced by reslurrying the fumed oxides in solutions of yttrium salts, spray-drying and calcining. The co-hydrolysis of premixed AlCl 3TiCl 4 vapours gave ultrafine oxide powders. Preparation of silica-doped materials was realized by adding SiCl 4 to the chloride mixture. The influence of the flame temperature on the specific surface area, the X-ray structure and the loose bulk density of the powders was investigated. In every case we obtained amorphous products. The high homogeneity and the fine particle size of the powders cause an extraordinary sintering activity.