SYNTHESIS OF CERAMIC OXIDE POWDERS BY MICROWAVE PLASMA PYROLYSIS

Ceramic powders prepared pyrolytically exhibit homogeneity and, in mos t cases, small grain sizes. The energy efficiency of electrically heat ed systems performing the pyrolysis in a stream of carrier gas is poor . Similar considerations concerning energy demand are valid for spray drying of suspensions. This situation can be improved using a microwav e plasma as a source for thermal energy. The process described in this paper works with any aqueous solution of salts used as starting mater ial in ceramics. The process was demonstrated by the synthesis of alum ina, zirconia, and zirconia-based ceramic powders; where an energy eff iciency of more than 80% was found. For the powder synthesis, aqueous solutions of the nitrates were used as starting materials. Through pro per selection of conditions for synthesis, it is possible to obtain na nocrystalline powders, as demonstrated by electron microscopy. Because of the extreme conditions associated with plasma during synthesis, it is possible to prepare non-equilibrium structures and solid solutions in systems in which nearly no equilibrium solubility exists.