Production of finely divided acicular magnetic iron oxides

US3947502A · kind A · utility

Assignee

• BAYER HEALTHCARE LLC · DE

Inventors

• Lutz Leitner · Krefeld, DE
• Franz Hund · Krefeld, DE

Key dates

• Filing date: Jan 11, 1973
• Grant date: Mar 30, 1976
• Expiry date: Jan 11, 1993

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C01P2006/80
• WIPO field: Audio-visual technology
• WIPO sector: Electrical engineering

Abstract

In the production of acicular, ferromagnetic iron oxide of high coercive force by oxidizing an iron (II)-hydroxide suspension with an oxygen-containing gas to form acicular iron (III) oxide hydroxide and dehydrating the iron (III) oxide hydroxide, optionally tempering, reducing and/or reoxidizing this into magnetic iron oxide, the improvement which comprises effecting the oxidation of the iron (II)-hydroxide suspension at a pH of at least about 13, the suspension including SiO.sub.2 in the form of a sol or soluble salt, the resulting iron (III) oxide hydroxide having SiO.sub.2 deposited thereon.