Process for producing cobalt- and iron-containing ferromagnetic powder by heat-treatment in the presence of an oxidizing agent
AssigneeFuji Photo Film Co., Ltd.
InventorsKoji Sasazawa, Shin-Ichiro Dezawa, Tatsuji Kitamoto
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Abstract
A Co- and Fe-containing ferromagnetic iron oxide powder having a high coercive force and improved stability to heat and pressure is produced by adding an aqueous alkali solution, an aqueous solution containing Co.sup.+2 ions, and an aqueous solution containing not more than 1 equivalent, based on the Co.sup.+2 ions, of Fe ions to a suspension of ferromagnetic iron oxide, and heating the mixture at a temperature of at least 80.degree. C in the presence of an oxidizing agent. The ferromagnetic iron oxide powder is especially suitable for producing magnetic recording media.
Claims21
A process for producing a Co- and Fe-containing ferromagnetic iron oxide powder which comprises adding to a suspension of an acicular ferromagnetic iron oxide an oxidizing agent, an aqueous alkali solution, an aqueous solution containing Co.sup.+2 ions and an aqueous solution of Fe ions and heat treating the resultant mixture, at a temperature of at least about 80.degree. C
- said CO.sup.+2 ions being present in said aqueous solution containing Co.sup.+2 ions in an amount of 0.5 to 10 atomic percent based on the amount of iron present in the acicular ferromagnetic iron oxide, said Fe ions being added to the suspension in an amount of at least 0.1 equivalent but not more than 1 equivalent based on the Co.sup.+2 ions, said aqueous alkali solution containing an amount of alkali such that after neutralizing the Co.sup.+2 ions and the Fe ions, the hydroxyl ion concentration is at least 0.5 mol/liter;
- and the amount of oxidizing agent, when it is a gas, is at least 0.1 liter/min per liter of the suspension and when it is a liquid or solid, the amount is at least 0.1 equivalent based on the Co.sup.+2 ions.
Dependencies are inferred from the claim text.