Bayer Aktiengesellschaft

Ulrike Pitzer

Gerhard Franz

Benno Laubach

Wilfried Burow

Wolfgang Oehlert

Heribert Bade

Gunter Buxbaum

Rolf Naumann

Klaus Lerch

Rolf-Michael Braun

The invention relates to the use of synthetic (synthetically produced) iron raw materials to prepare iron oxide pigments in the Penniman process and other iron-dissolution processes.

Use of synthetic, iron raw materials for preparing iron oxide pigments

Non-silking iron oxide yellow pigments with high color density. Iron oxide yellow pigments in the .alpha.-FeOOH modification with a silking index of less than 5 were obtained in which

Non-silking iron oxide yellow pigments with high color density

The present invention relates to a process for the production of yellow, highly transparent iron oxide pigments of elevated chemical purity, to yellow iron oxide pigments obtainable in this manner and to the use thereof to color lacquers and plastics.

Highly transparent, yellow iron oxide pigments, process for the

The invention relates to very highly transparent iron oxide pigments with high color saturation, to a process for their production and to their use for pigmenting paints and plastics.

Very highly transparent yellow iron oxide pigments, a process for their

The present invention relates to a process for the production of red, transparent iron oxide pigments of elevated chemical purity, to iron oxide pigments obtainable in this manner and to the use thereof to color lacquers and plastics.

Highly transparent, red iron oxide pigments, process for the production

The invention relates to transparent iron oxide pigments having an average particle size, based on the longest needle axis, of less than 0.1 .mu.m, to processes for their production and to their use for pigmenting lacquers and plastics.

Transparent iron oxide pigments, processes for their production and

Silicon nitride powder having a total oxygen content of less than 1.8% by weight and an isoelectric point in 0.001M aqueous KNO.sub.3 solution of below pH 4 is prepared by calcining Si.sub.3 N.sub.4 powder having an oxygen content of 0.4% by weight or less in an oxygen containing atmosphere at temperatures between 700.degree. and 1200.degree. C. for 15 to 90 minutes or by grinding such as Si.sub.3 N.sub.4 powder in water, lower alcohol or a water/alcohol mixture for 15 to 120 minutes.

Silicon nitride powders of low isoelectric point and processes for their

Si.sub.3 N.sub.4 powders having a total oxygen content of less than 1.8% by weight with the proportion of surface oxygen content of more than 65% of the total oxygen content, and having a fluorine content of less than 35 ppm are prepared by annealing Si.sub.3 N.sub.4 powders having a total oxygen content of less than or equal to 0.4% by weight in an oxygen-containing atmosphere at temperatures of 700.degree. C. to 1200.degree. C. for 15 to 90 minutes or by grinding Si.sub.3 N.sub.4 powders having a total oxygen content of less than or equal to 0.4% by weight in water, alcohol or aqueous alcohol 15 to 120 minutes.

Silicon nitride powders with improved surface properties and processes

Si.sub.3 N.sub.4 powder wherein the total oxygen content of the powder is 0.4% by weight or less is produced by preparing an amorphous Si.sub.3 N.sub.4 intermediate by reacting a Si-containing compound with an N-containing compound and the intermediate is then crystallized wherein 'P', multiplication product of

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Krefeld, Germany

Ulrike Pitzer