Bayer Aktiengesellschaft

Axel Westerhaus

Gunter Buxbaum

Horst Brunn

Bernd Krockert

Jurgen Wiese

Karl-Werner Ganter

Jurgen Scharschmidt

A pigment useful for coloring building materials such as bricks is a heat-stable isometric iron oxide brown pigment of .gamma.-Fe.sub.2 O.sub.3 structure which has a silicon content, expresed as SiO.sub.2, of 0.1 to 12% and an Al content, expressed as Al.sub.2 O.sub.3, of 0.02 to 5%.

Heat stable iron oxide pigments of upsilon-Fe.sub.2 O.sub.3 structure, a

Pigments for printing inks and magnetic toners are iron oxide pigments with a rhombic dodecahedral form and an average particle diameter of from 0.05 to 3.0 .mu.m with a standard deviation of the particle size distribution of .+-.30%.

Iron oxide pigments, a process for their preparation and their use

Iron oxide black pigment with improved color intensity is produced by subjecting finely divided pigment obtained from reaction of metallic iron with aromatic nitro compounds to a heat treatment of 200.degree. to 800.degree. C. under a non-oxidizing atmosphere for a time of 2 minutes to 5 hours.

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Krefeld, Germany

Axel Westerhaus