Preparation of cobalt-containing, acicular, magnetic iron oxides

摘要

Acicular, magnetic iron oxide consisting of a core of gamma-iron(III) oxide and a ferrite shell containing a total of from 0.4 to 12% by weight of cobalt(II) ions and from 0.1 to 15% by weight of iron(II) ions, the percentages being based on the total amount of magnetic material, is prepared by a process in which an iron(II) hydroxide precipitate is applied to the gamma-iron(III) oxide core in a first stage and an iron-(II)/cobalt hydroxide precipitate is applied to the said core in a second stage, and the core is then converted to the ferrite shell by oxidation.