Chromium oxide pigment from sodium chromate dihydrate plus ammonium salt

US4040860A · kind A · utility

Assignee

• BAYER HEALTHCARE LLC · DE

Inventors

• Manfred Mansmann
• Wolfgang Rambold · Krefeld, DE

Key dates

• Filing date: Feb 6, 1976
• Grant date: Aug 9, 1977
• Expiry date: Feb 6, 1996

Classification

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

Abstract

In the production of chromium oxide green pigment by heating a substantially stoichiometrically equivalent mixture of sodium dichromate dihydrate and an ammonium salt selected from the group consisting of the sulfate and chloride, the improvement which comprises dry mixing sodium dichromate dihydrate having a particle size less than 2 mm with the ammonium salt having a particle size less than about 0.5 mm, heating the resulting mixture over a period of about 15 minutes to a pigment-forming temperature of about 800.degree. to 1100.degree. C, calcining the mixture at a temperature in that range, and separating the formed pigment from the salts. To the mixture prior to heating there may be added sodium hydroxide solution, boron compounds such as borax and/or organic modifiers such as sawdust which improve the color and tinting strength of the resulting pigment. The pigments are brighter, and of higher tinting strength than heretofore produced.