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Abstract

In one aspect, the present invention concerns a process of making coated magnetic particles. According to this process, an aqueous sol of amorphous, hydrolyzed, aluminous, colloidal particles is mixed with an aqueous suspension comprising magnetic particles. The amorphous, hydrolyzed, aluminous, colloidal particles have a mean particle size in the range from about 0.5 to about 5 nanometers and an average degree of hydrolysis in the range from 1.5 to about 3. During mixing, the amorphous, hydrolyzed, aluminous, colloidal particles form a continuous, amorphous, aluminum hydrous oxide coating on the magnetic particles, wherein the coating has an average thickness in the range from about 0.5 to about 5 nanometers. The present invention also concerns coated magnetic particles. Coated magnetic particles according to the present invention comprise a magnetizable core and a continuous, amorphous, aluminum hydrous oxide coating formed on the magnetizable core. The coating has an average thickness in the range from about 0.5 to about 5 nanometers. In another aspect, the present invention concerns a magnetic recording medium comprising a magnetic layer formed on a nonmagnetizable support. The magnetic layer comprises the coated magnetic particles described above dispersed in a polymeric binder.

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First Claim