INFLUENCE OF SLURRY FLOCCULATION ON THE CHARACTER AND COMPACTION OF SPRAY-DRIED SILICON-NITRIDE GRANULES

The effect of slurry flocculation on the characteristics of silicon ni tride granules prepared by the spray drying process is investigated. T he flocculation state of an aqueous silicon nitride slurry is controll ed by adding nitric acid and evaluated as a function of pH. Dense and hard silicon nitride granules result from a well-dispersed slurry havi ng a high pH (e.g., 10.8). These hard granules retain their shape in g reen compacts and form detrimental defects. Lowering the pH of the slu rry to a certain value (e.g., pH 7.9) results in slurry flocculation. Granules prepared from this flocculated slurry have low density and lo w diametral compression strength and contribute to the elimination of large pores in green compacts.