US 6,673,143 B2Granted

Aqueous slurry of rare earth hydroxide particles

AssigneeShin-Etsu Chemical Co., Ltd.

InventorsShigeru Sakai, Yuji Kimura

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Abstract

An aqueous slurry of rare earth hydroxide particles which is particularly suitable for use as a sintering aid of a ceramic powder such as silicon nitride. The aqueous slurry, which is characterized by the very small average diameter of the primary particles and a low electric conductivity as well as outstandingly high stability against settling of the particles, can be prepared by a process comprising the steps of: (a) precipitating rare earth hydroxide particles by mixing aqueous solutions of a rare earth compound, e.g., nitrate, and a basic compound, e.g., ammonia, preferably, in the presence of a surface active agent; (b) collecting the precipitates to give a cake; (c) washing the cake with deionized water until the electric conductivity of the washing has decreased to 3 mS/cm or lower; and (d) re-dispersing the thus washed cake in deionized water.

Claims11

Dependent claims

An aqueous slurry of particles of a rare earth hydroxide, of which the primary particles of the rare earth hydroxide have a particle diameter not exceeding 150 nm, having an electric conductivity not exceeding 2 mS/cm at room temperature, said slurry produced by a process which comprises the steps of:

(a) mixing an aqueous solution of a water-soluble rare earth compound and an aqueous solution of a basic compound to precipitate rare earth hydroxide particles in an aqueous precipitation medium;
(b) collecting the rare earth hydroxide particles by separating from the aqueous precipitation medium to give a cake of the rare earth hydroxide particles;
(c) repeatedly washing the cake of the rare earth hydroxide particles with deionized water until the washing has an electric conductivity not exceeding 3 mS/cm at room temperature;
and
(d) dispersing the rare earth hydroxide particles in deionized water as a dispersion medium to give an aqueous slurry.

2 more elements

Dependencies are inferred from the claim text.