Reduction of time-dependent change of coercive force and Iron(II) content by silica and aluminum hydrate coating onto Co-magnetite fine particles

In order to improve the magnetic and chemical stability of Co-magnetite fin e particles, silica and aluminum hydrate coating onto the surface of Co-mag netite particles in aqueous slurry is investigated experimentally. The time -dependent change of coercive force and Iron(II) content for Co-magnetite f ine particles are lessened by this silica and aluminum hydrate coating meth od. This means that the magnetic and chemical stability is improved by this wet-type coating method. It is considered that these Co-magnetite fine par ticles are protected from oxidation sufficiently enough because of the coat ing layer of 0.5 similar to 1.0nm in thickness based on silica and aluminum hydrate surface treatment. This experimental result is roughly in agreemen t with the estimated thickness based on the uniformly covered surface layer model. When coated Co-magnetite particles are applied to magnetic recordin g media, there is no disadvantage of tape properties by silica and aluminum hydrate coating, and it becomes clear that the available magnetic tape wit h both good magnetic property and good stability can be prepared in this in vestigation.