INFLUENCE OF ZIRCONIA ADDITION ON THE SINTERING BEHAVIOR OF BIMODAL SIZE DISTRIBUTED ALUMINA POWDER MIXTURES

Fine zirconia powder was added to the bimodal size distributed alumina powder mixtures and the influence of zirconia addition on the sintering behavior of the powder mixtures was investigated. At low firing temperature, that is, in the initial stage of sintering, zirconia retarded the densification of the powder mixtures and also enlarged the pore size of the compacts. At high firing temperature, the influence of zirconia addition was different depending on the packing structure of the green compact. When the coarse alumina particles were dispersed in the matrix of the fine particles, zirconia promoted the densification of the mixtures. This result was explained by the promotion of the densification between the fine and the coarse alumina particles in the intermediate stage of sintering and by the migration of zirconia and the hindrance effect of zirconia on the grain growth of alumina in the final stage of sintering. When the coarse alumina particles formed a skeletal structure, zirconia did not promote the densification of the mixtures. This result was explained by the dependence of the densification of the compacts only on the densification among the coarse alumina particles.