Origin of shrinkage anisotropy during sintering for uniaxially pressed alumina compacts

Origin of shrinkage anisotropy during sintering is reported on alumina powder compacts made by uniaxial pressing followed by cold isostatic pressing (CIP). Two types of alumina particles were used in this study; one was slightly elongated shape, the other spherical shape. An anisotropic shrinkage occurred during sintering in the compacts made of the elongated shape of particles, even after the CIP. However, no the anisotropic shrinkage happened in the compacts made of the spherical shape of particles, even at the same processing condition to the former. Detailed structure analysis involving the novel immersion liquid technique showed that the particle orientation was found to be an important origin of the shrinkage anisotropy. The particle orientation was developed during uniaxial pressing in the compacts of the elongated shape of particles. Subsequent CIP did not eliminate the shrinkage anisotropy. No particle orientation happened in the compact of the spherical shape of particles.