Production of precipitated red iron (III) oxide pigment relatively free of .alpha.-FEOOH

US3946103A · kind A · utility

Assignee

• BAYER HEALTHCARE LLC · DE

Inventor

• Franz Hund · Krefeld, DE

Key dates

• Filing date: Sep 19, 1973
• Grant date: Mar 23, 1976
• Expiry date: Sep 19, 1993

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C01P2002/52
• WIPO field: Basic materials chemistry
• WIPO sector: Chemistry

Abstract

In the production of a precipitated red iron (III) oxide pigment of hematite structure wherein an aqueous iron (II) salt solution is mixed with an aqueous alkali solution in substantially equivalent quantities to produce an aqueous suspension of iron (II) hydroxide or carbonate, the suspension is oxidized by passing oxygen-containing gases through it with stirring under atmospheric pressure at a temperature of about 0.degree. to 50.degree.C, and the resulting iron (III) seed suspension is allowed to grow into precipitated red iron (III) oxide pigment by further oxidation with an oxygen-containing gas at a temperature of about 50.degree. to 100.degree.C in the presence of more iron (II) salt and alkali solution or in the presence of iron (II) salt and metallic iron at a pH-value kept in the acid range, the improvement which comprises producing the iron (III) seed suspension in the presence of a foreign modifying substance so that lattice-distorted, chemically reactive finely divided delta-FeOOH seeds are formed, whereby the resulting red iron (III) oxide pigment contains less than about 15 % by weight of .alpha.-FeOOH. The modifying substance may be a chloride of magnesium, calcium …