Microstructure of alumina compact body made by slip casting

An attempt was made to understand the structural changes and particle-packing behavior of compacted alumina (α-Al2O3) made by slip casting. Packing structure of powder particles was examined in alumina compact made by slip casting with the crossed polarized light microscope in the transmission mode. Anisotropic structure was present in the specimen. A repeated change of color was noted with the rotation of the specimen at every 45° increments in the cross-section of compact cut parallel to the flow direction of water in the casting process. The alumina particles were aligned with the longest axis normal to the flow direction. The center of the cross-section showed a rather disordered packing structure. Isotropic optical property was noted in the specimen cut perpendicular to the flow direction. Isotropic microstructure was found in all directions of the compact made by the spontaneous drying process, in which less apt water flow occurred during drying. The development of anisotropic structure was insensitive to the dispersing state of particles in the slurry.