| 摘要 |
Solids that are subject to a deleterious reaction with a dispersion medium in which they are suspended can be safely comminuted in that dispersion medium by providing therein a surfactant capable of reacting with the solid at a faster rate than the dispersion medium can so react to thereby suppress the deleterious reaction. In particular, unsintered silicon nitride or silicon carbide which when contacted with water would decompose to form silica on their surfaces can be milled in water, without producing excessive amounts of silica. The dispersions produced are sufficiently stable to be filtered through openings of 2 microns with loss of no more than 5% of the silicon nitride or carbide. Stable dispersions of solids in liquids can be coated with a different solid by surface precipitation under conditions which preclude the formation of a bulk precipitate. Thus, ceramic nitride or carbide particles are coated with densification aids, such as yttria, by the surface precipitation of the corresponding hydroxides on the ceramic particles in water. Ceramic powders prepared in this way densify to give products with moduli of rupture and fracture toughnesses at least as high as those made from powders conventionally milled in alcohol with lower amounts of densification aid.
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