| 摘要 |
1,264,994. Magnetic materials. MINNESOTA MINING & MFG. CO. 18 Feb., 1969 [19 Feb., 1968], No. 8802/69. Heading H1H. [Also in Division C1] Iron oxide modified with cobalt oxide is made by forming a suspension or slurry of acicular water - insoluble particles of gamma - Fe 2 O 3 , FeOOH or dehydrated FeOOH either with cobalt hydroxide or cobalt carbonate, or in a solution of a cobalt salt from which a cobalt compound is precipitated on the iron oxide particles; decanting, washing, filtering and drying the particles as necessary; heating the mixture of iron oxide and cobalt compound in an inert atmosphere to a temperature sufficient to decompose the cobalt compound and thereby modify the iron oxide particles with cobalt oxide in an amount corresponding to 0À25-22À4 wt. per cent of cobalt based on the iron oxide. An additional heating step in a reducing atmosphere may be carried out to provide 3-20% by wt. of FeO. When the suspension contains FeOOH or dehydrated FeOOH, additional steps of reducing the cobalt-modified particles to Fe 3 O 4 and then oxidizing to gamma Fe 2 O 3 . The modified particles have, when combined with half their weight of non-magnetizable binder, a coercivity (He) of more than 350 Oersteds in the direction of orientation after physical orientation, and a value of the product of He and the square of the ratio of loss of saturated remanence perpendicular to particle orientation to loss of saturated remanence parallel to particle orientation of at least 2205 after 30 minutes at 150‹ C. Recording media, e.g. tapes, are made by mixing the magnetic particles with sufficient non-magnetic binder, e.g. polyesterurethane to give He more than 350 Oe. and a remanent magnetization Br exceeding 650 gauss in the direction of particle orientation; coating on to a non-magnetic backing, aligning in a magnetic field and hardening. Such media have a saturated remanence retention greater than 80% after 30 minutes at 150‹ C. Examples describe the preparation of modified particles by (1) precipitating cobalt hydroxide on acicular gamma-Fe 2 O 3 ; (2) adding cobalt hydroxide particles to an aqueous slurry of gamma-Fe 2 O 3 ; precipitating cobalt carbonate on to gamma-Fe 2 O 3 and precipitating cobalt hydroxide on to acicular FeOOH. |
