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

The thermal shock resistance of brittle materials such as glass and ce ramics is one of their weaknesses. Pores and above all incorporated se cond phases in these materials alter these properties which are decisi ve for thermal shock behavior, and may therefore increase this behavio r in a precalculable manner. The present paper will first theoreticall y demonstrate when and why porosity leads to an improvement in thermal shock resistance. The thermal shock resistance for porous borosilicat e sintered glass and porous eutectic calcium titanate ceramic are calc ulated and compared to experimental values. They confirm - that low po rosities lead to an improvement in thermal shock resistance - that the thermal shock resistance has a maximum at a certain porosity and - th at above certain porosities the presence of pores deteriorates the the rmal shock resistance. If one considers porous materials as a special case of composite materials then relations valid for composite materia ls can be transferred to porous materials (''composite material concep t'') and viceversa. This is investigated using the examples of borosil icate 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 wer e calculated and confirmed experimentally, while for calcium titanate- paladium composite materials a 15% improvement in thermal shock resist ance was already achieved with about 5 vol% of the metallic phase.