Process for preparing magnetic iron oxide and magnetic iron oxide produced thereby
AssigneeFuji Photo Film Co., Ltd.
InventorsKoji Sasazawa, Shigeo Komine, Tatsuji Kitamoto, Goro Akashi
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Abstract
A magnetic iron oxide having a large coercive force and an improved squareness ratio prepared by coating the surface of needle-like particles of magnetic iron oxide with a cobalt compound, placing the coated iron oxide particles in a unidirectionally oriented magnetic field thereby orienting the particles in the direction of the magnetic field, and heat-treating the needle-like particles in this state with the application of an external magnetic field, or heat-treating the needle-like particles in a magnetized state.
Claims10
A process for preparing magnetic iron oxide, which comprises,
- (a) coating the surface of needle-like particles of magnetic iron oxide with a cobalt compound, said iron oxide having the formula FeO.sub.x wherein x is from about 1.36 to 1.49,
- (b) placing the coated iron oxide particles in a unidirectionally oriented magnetic field of at least about 300 Oe, thereby to orient most of the needle-like particles in the direction of said magnetic field,
- (c) heat-treating said needle-like particles at a temperature of from about 200.degree. to 800.degree. C., in an atmosphere of inert gas, and
- (d) conducting said heat treating while said needle-like particles are in a magnetized state or, if said needle-like particles are not in a magnetized state, then conducting said heat treating while simultaneously applying an external magnetic field to said needle-like particles.
Dependencies are inferred from the claim text.