Production of ceramic powders by emulsion precipitation processes and

Abstract

The invention provides new processes for the production of precursor powders for ceramic materials by emulsion precipitation, the new processes permitting the economic production with at least some cations of uniformly small size particles (1 micrometer or less) to result in corresponding dense microstructures upon sintering the precursor powder to produce the ceramic material. The processes require the production of a fine water-in-oil type emulsion of an aqueous solution of the desired cation or cations in a non-miscible liquid, usually an oil, such as a saturated hydrocarbon, a suitable surfactant usually also being employed, The emulsion preferably has an aqueous particle size of 0.1 micrometer or less, produced by a mechanical emulsator. A gaseous reactant, preferably ammonia, or a mixture of ammonia with a neutral diluent gas, is bubbled through the emulsion to contact it and react with the cations, without breaking the emulsion by physical and/or chemical action. The emulsion becomes alkaline and may gell if the aqueous content is sufficiently high. Upon removal of the water and the non-miscible liquid, by heating, spray drying, freezing, etc., the particles that remain are found to have retained their fine structure without agglomerating. If one or more of the cations is of the type that forms complexes with ammonia it may be preferred to instead use a non-complexing gaseous reactant, such as carbon dioxide.