Processing defects in ceramic powders and powder compacts

Structure and defects in powders and powder compacts are examined in detail to determine their formation mechanisms, and their relevance to the production of high quality ceramics. New characterization tools that are indispensable in the characterization of defect structure are described with the aid of schematic illustrations. Defects such as aggregates and large particles are present in all powders examined, even after rigorous grinding. These short-range defects degrade the properties and the quality of a sintered ceramic. Long-range defects due to particle orientation and anisotropic particle packing are also common in powder compacts, and are attributed to a shear stress field and/or a directional stress field during forming. Particle packing anisotropy produces long-range defects that are responsible for anisotropic deformation and cracking during drying and sintering.