Bayer Aktiengesellschaft

Gerhard Trenczek

Jakob Rademachers

Heinrich Heine

Wolfgang Rambold

Hans-Ulrich Hofs

Dieter Rade

Gunther Teichmann

Bruno Raederscheidt

Chrome green oxide useful, inter alia, as a coloring material and having a water number of 10 to 40 g/100 g is prepared by adding sulphonic acid compounds, polyphosphoric acid compounds, polyacrylic acid compounds or mixtures thereof, in quantities of from 0.1 to 2% by weight, to an aqueous suspension of chrome oxide green pigment having a BET surface area of from 1 to 20 m.sup.2 /g before drying, and then drying the suspension.

Chrome oxide green, a process for its preparation and its use

A process for the production of low sulphur chromium(III) oxide comprising annealing at a calcining temperature from about 800.degree. C. to 1100.degree. C. a mixture of alkali metal chromate and about 0.7 to 0.96 times its molar amount of ammonium sulfate, and separating the chromium(III) oxide formed from the alkali metal salt. Advantageously the ammonium sulfate in the form of a concentrated solution is mixed with solid alkali metal dichromate and the mixture thereafter is adjusted prior to calcination to a water concentration of less than about 15% by weight of water.

Production of low sulphur chromium (III) oxide

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Krefeld, Germany

Gerhard Trenczek