S. Fukuhara, M. Tahara, N. Miwa, K. Ashitaka, K. Tamai, H. Morinaga, S. Ogitani
Keywords: cubic particle, alumina, particle size distribution, crystal form
Summary:Alumina is chemically stable and excellent in hardness, heat resistance, and mechanical properties. That is the reason alumina is widely used as a structural material, an abrasive grain and a cutting tool. In general, alumina powder is manufactured by milling mass of sintered or melted alumina at high temperature followed by grading. The alumina powder obtained by such a brake-down method has following issues: 1. the powder shape is not uniform. 2. the particle size distribution (PSD) is wide. These issues could cause non-uniform compact density and formability when, for example, used as a raw material of ceramics, and could leave scratches and residue of abrasive grains on substrates when used as a raw material of abrasive grains. We have succeeded to synthesize unique cubic alumina having uniform shape and narrow PSD by using build-up method (hydrothermal synthesis). In this method, a raw material is dissolved first followed by the particle growing under heart and pressure. The precise control of synthesis condition enables to provide reproducible shape and size of particles. The precise control of the following heat treatment gives us various crystalline alumina (boehmite, gamma, delta, theta, alpha) having various hardness without changing their shapes.