Processing defects in ceramic powders and powder compacts

•New examination with new characterization methods based on liquid immersion microscopy.•Explicit images of packing structures and their classification into short range and long range structures.•Presence of few large particles and their behavior in grinding.•Relevance of the short range structures with the quality of ceramics.•Relevance of the long range structures with the troubles in production of ceramics.

sStructure 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.

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