Bayer Aktiengesellschaft

Hans-Peter Biermann

Heinrich Heine

Rolf Naumann

Gunter Buxbaum

Jakob Rademachers

Artur Botta

Helmut Steinberger

Bernd Krockert

Wolfgang Rambold

Lutz Leitner

Hans-Ulrich Hofs

Helmut Printzen

Peter Kohler

Detlef Melzer

Erhardt Tabel

Low-silking iron oxide yellow pigments having improved color qualities are produced by a novel method which utilizes both precipitation process and the Penniman process. Pigments are nucleated and grown by precipitation to achieve multiplication factor of 2.5 to 7 and additional pigment growth is carried out by the Penniman process.

Process for the production of iron oxide yellow pigments

Acidic liquids, such as galvanic electrolyte solutions for metal electroplating, contain a surfactant and a foam inhibiting agent which is a perfluoroalkyl-containing ester of phosphoric acid.

Antifoaming additive for acid liquids

Iron oxide particles containing at least 5% by weight of iron (II) content calculated as FeO are stabilized against atmospheric oxidation by a coating of at least one compound containing boron and those particles are useful as coloring pigments and magnetic particles in magnetic recording media.

Thermostable iron oxide pigments

Spherical agglomerates of surface-stabilized primary particles substantially consisting of iron, having a BET surface of about 5 to 50 m.sup.2 /g, measured on the agglomerate, in non-pyrophoric form and having a bulk density of about 0.5 to 2.0 kg/l and an agglomerate diameter of about 0.5 to 10 mm are produced by

Agglomerated ferromagnetic iron particles

A pigment of a magnetic metal or alloy thereof carrying, in about 0.2 to 30% of the weight of the metal or alloy, a coating of at least one member selected from the group consisting of an ortho-silicic acid ester, a hydrolyzate thereof and a condensation product thereof. Optionally it also carries a corrosion inhibitor. The coated pigment is produced by suspension of the untreated pigment in a liquid medium containing the ortho-silicic acid ester or derivative thereof, and optionally the corrosion inhibitor, followed by separation and drying at 50.degree. to 250.degree. C. The resulting pigment is non-pyrophoric and of high performance properties suitable for use in magnetic recording media.

Magnetic metal and alloy pigments

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Krefeld, Germany

Hans-Peter Biermann