Acicular cobalt-modified iron oxides and their preparation
AssigneeBASF SE
InventorsEkkehard Schwab, Ronald J. Veitch, Helmut Auweter
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Abstract
Acicular, cobalt-modified iron oxides consisting of a core of an iron oxide of the formula FeO.sub.x where x is from 1.33 to 1.5 and a ferrite shell which contains a total amount of from 0.4 to 12% by weight of cobalt ions and not more than 5% by weight of iron(II) ions, the percentages being based on the total amount of the material, which iron oxides have improved aging resistance, particularly with regard to the coercive forces, and a process for their preparation.
Claims2
An acicular, cobalt-modified iron oxide consisting of a core of an iron oxide of the formula FeO.sub.x where x is from 1.33 to 1.5 and ferrite shell which contains a total amount of from 0.4 to 12% by weight of cobalt ions and not more than 5% by weight of iron(II) ions, the percentages being based on the total amount of the material, wherein this cobalt-modified iron oxide has an alkali metal silicate adsorbed on its surface and an isoelectric point corresponding to pH.ltoreq.6.5 and the coercive force decreases by less than 5% after storage in air for 21 days at 50.degree. C.
Dependencies are inferred from the claim text.