INCREASING THE THERMAL-SHOCK RESISTANCE OF SINTERED GLASS AND CERAMICS BY THE COMPOSITE-MATERIALS CONCEPT

The thermal shock resistance of brittle materials such as glass and ceramics is one of their weaknesses. Pores and above all incorporated second phases in these materials alter these properties which are decisive for thermal shock behavior, and may therefore increase this behavior in a precalculable manner. The present paper will first theoretically demonstrate when and why porosity leads to an improvement in thermal shock resistance. The thermal shock resistance for porous borosilicate sintered glass and porous eutectic calcium titanate ceramic are calculated and compared to experimental values. They confirm - that low porosities lead to an improvement in thermal shock resistance - that the thermal shock resistance has a maximum at a certain porosity and - that above certain porosities the presence of pores deteriorates the thermal shock resistance. If one considers porous materials as a special case of composite materials then relations valid for composite materials can be transferred to porous materials (''composite material concept'') and viceversa. This is investigated using the examples of borosilicate sintered glass with incorporated antimony particles and eutectic calcium titanate ceramic with incorporated paladium particles. In the case of the glass-antimony composite material, improvements in thermal shock resistance of about 15% with 10 vol% antimony incorporation were calculated and confirmed experimentally, while for calcium titanate-paladium composite materials a 15% improvement in thermal shock resistance was already achieved with about 5 vol% of the metallic phase.