THE EFFECT OF PROCESSING VARIABLES ON THE MECHANICAL AND ELECTRICAL-PROPERTIES OF BARIUM-TITANATE POSITIVE-TEMPERATURE-COEFFICIENT-OF-RESISTANCE CERAMICS .1. ADDITIVES AND PROCESSING PRIOR TO SINTERING

The effect of processing variables on the mechanical and electrical properties of barium-titanate positive-temperature-coefficient-of-resistance (PTCR) ceramics has been studied. In the first part of this investigation the effect of changes to processing prior to sintering have been compared. This has highlighted the importance of slow compaction rates and the presence of soft agglomerates in the preparation of strong compacts. The addition of a binder prior to milling has been found to improve the strength of the-sintered material by up to 50% by encouraging the formation of smaller, less damaging, pores. Strength, measured by diametral compression of discs, was found to be highly dependent on the density of the ceramic. Typically, the presence of a 22% porosity leads to a 75% reduction in strength compared to samples containing only a 1% porosity. No systematic effect of grain size on strength was observed.