Alkaline Furnace Process
Bauxite is finely ground and mixed with alkali or alkaline earth carbonates and sintered to produce aluminate. By calcining ammonium alum at about 1200oC high purity alumina powder is prepared. While heating, the alum melts and forms a viscous liquid. On further heating water is expelled, ammonia and sulphur trioxide are removed and alpha alumina with low bulk density is formed. The practical size is about 0.1 micron. This is a very pure form of Alumina powder. Even ultra pure and ultra fine powders of specific morphology can be prepared by sophisticated methods like freeze drying, hydro thermal precipitation, plasma synthesis and solgel technique.
