Origin of shape deformation during sintering of alumina compacts

Alumina compacts were prepared by uniaxial pressing followed by cold isostatic pressing (CIP), and their structures were examined by both conventional and novel methods to clarify the origin of deformation during sintering. A novel liquid immersion method revealed the presence of anisotropic packing structures in all the compacts even after CIP. Alumina particles of slightly elongated shape tended to be aligned with their largest face normal to the direction of applied pressure in the uniaxial pressing. Correspondingly, the shrinkage during sintering was always larger in the direction parallel to uniaxial pressing as compared to that normal to it. Other conventional characterization methods including scanning electron microscopy (SEM) and powder X-ray diffraction failed to reveal the presence of a unique anisotropic packing structure.