Upgrading technical ceramics

Abstract

Technical ceramics, in particular engineering ceramics, could benefit substantially from the elimination of surface defects. This will result in a marked enhancement of their strength and corrosion resistance. This effect can be achieved by coating these ceramics by chemical vapour deposition (CVD). By coating a ceramic material using essentially the same material applied by a suitable CVD process surface porosity and surface cracks can be virtually eliminated. In many of today's technical ceramics densification is achieved by liquid-phase sintering. The resulting grain boundary phases are, in many cases, an important factor in the corrosion damage of ceramic materials. CVD coating can effectively shield off those grain boundary phases from the corrosive medium. This markedly enhances the corrosion resistance. At the Centre for Technical Ceramics at Eindhoven University of Technology a research program was recently initiated in order to determine systematically the potential of this approach. In this presentation a literature survey is given of results obtained by other workers together with some preliminary results of our own. The latter concern the upgrading of reaction bonded silicon nitride and sintered AIN. A number of potential applications of this approach are indicated. The limitations of this upgrading of technical ceramics by CVD are also discussed.