Effects of Forming and Sintering Methods on the Microstructure and Electrical Conductivity of 8, 8"-Alumina Sintered Body

Abstract

In the preparation of β, β″-alumina sintered body from its powders with the composition of O.87Na2O·O, 6MgO·5Al2O3 which were produced by a spray pyrolysis technique, the effects of forming and sintering conditions on the microstructure (duplex structure and grain orientation)and anisotropy of electrical conductivity of the sintered body were investigated. The density of green compact was dependent on the forming method and increased in the order uniaxial press(A) <uniaxial pressing after granulation(B)<isolatic pressing after granulation (C). On firing at 1560-1620°C for 5-90 min, the microstructure of sintered body tended to become a duplex structure due to abnormal grain growth as the density of green compact decreased. In green compact formed by method(B), the c-planes of β, β″-alumina particles oriented preferentially perpendicular to the press direction; the degree of orientation was increased markedly by firing. Forming method C gave green compact and sintered body with low degree of orientation, indicating that the dense compaction is essential to suppress the 1727preferential orientation of β, β″-alumina particles. The fraction of β″ phase in sintered body was higher as the grains grew into larger ones. The specific resistivity of sintered body in the press direction (pr) was generally larger than that in the perpendicular direction (pR). With increasing in the degree of particle orientation, pp increased markedly, whereas pa remained nearly constant.