Manufacture of ferromagnetic metal particles consisting essentially of iron

A method of preparing acicular ferromagnetic iron metal particles, said particles being modified at the surface with 0.02 to 0.2% by weight of carbon and with 0.5 to 1.9% by weight of phosphorus as phosphate, which comprises the steps of

• (a) dispersing acicular iron oxide hydrate in a solution of a hydrolysis-resistant substance selected from the group consisting of oxyacids of phosphorus, their esters and inorganic salts, and a compound selected from the group consisting of aliphatic, monobasic and tribasic carboxylic acids of from 1 to 6 carbon atoms;
• (b) removing the solvent by filtration and heating, whereby said hydrolysis-resistant substance based on oxyacids of phosphorus is applied to said iron oxide hydrate in such an amount that from 0.2 to 2% by weight of phosphorus is present, and said carboxylic acid is applied to said iron oxide hydrate in such an amount that from 0.1 to 1.2% by weight of carbon is present, and
• (c) reducing the so-treated acicular iron oxide hydrate by passing gaseous hydrogen at a temperature of from 230.degree. to 450.degree. over said treated iron oxide hydrate to form acicular iron metal particles retaining the acicular shape of the acicular iron oxide hydrate starting material.