| 简介 |
PROBLEM TO BE SOLVED : To improve oxidation resistance without degrading magnetic characteristics by uniformly adhering the particulate silica obtained. by hydrolysis of alkyl silicate to the particle surfaces of powder. SOLUTION : An alkyl silicate to be used is expressed by SinOn-1(OR)2n+2. R denotes an alkyl group and is more particularly preferably an ethyl group; n is a range from 1 to 10. The silica film is preferably formed by mixing the alkyl silicate with the magnetic powder and heating the mixture in an inert atmosphere. The amount. of the alkyl silicate to be added is preferably specified to 1 to 5 pts.wt. per 100 pts.wt. magnetic powder. When water is added to the mixture before the mixture is heated after this addition, the hydrolysis of the alkyl silicate is accelerated. The amount of the water to be added is preferably 0.1 to 3 times the theoretical value necessary for forming silica. The heating in the inert atmosphere is preferably executed at 60 to 250 deg.C. |
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