Oxidation of metallic iron to black oxide pigments

US4123501A · kind A · utility

Assignee

• BAYER HEALTHCARE LLC · DE

Inventors

• Klaus Kohler · Eschborn, DE
• Peter Woditsch · Krefeld, DE
• Karl-Heinz Schultz · Krefeld, DE

Key dates

• Filing date: Apr 14, 1977
• Grant date: Oct 31, 1978
• Expiry date: Apr 14, 1997

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C01P2006/60
• WIPO field: Materials, metallurgy
• WIPO sector: Chemistry

Abstract

A metallic iron-containing starting material such as iron filings, iron powder or a reduced ore such as ilmenite is oxidized with air in the presence of 5 to 40% of iron oxide and/or iron oxide hydroxide nuclei and about 2.5 to 200% of an electrolyte, percentages being based on metallic iron by weight. The oxidation is effected in aqueous suspension at 75.degree. to 100.degree. C and a pH of 4 to 6.5. If the nuclei are magnetite-free, at least the first quarter of the oxidation should be at pH 5 to 6.5. Preferred electrolytes are transition metal salts. The pigments are more intense in color and have a more pronounced blue tinge.