Bayer Aktiengesellschaft

Ingo Pflugmacher

Franz Hund

Gunter Buxbaum

Peter Woditsch

Jakob Rademachers

Volker Hahnkamm

Wolfgang Rambold

Gerhard Winter

Lutz Leitner

Peter Kiemle

In the preparation of highly orientatable needle-shaped ferrimagnetic iron oxide particles by the reduction and reoxidation of needle-shaped particles of hydrated oxide of iron which have been surface treated against sintering the improvement which comprises effecting the surface treatment by applying to the particles of hydrated oxide of iron one layer of oxygen-containing anions and a further layer of polyvalent cations, each layer weighing about 0.02 to 2% by weight of the particle. Advantageously, the polyvalent cation-containing layer is applied between two oxygen-containing anion layers, the oxygen-containing anions used are selected from the group consisting of silicate, phosphate, borate, vanadate, molybdate and tungstate, the polyvalent cations used are selected from the group consisting of aluminum, chromium, manganese, iron and gallium, each layer weighs about 0.1 to 1% of the weight of the particles and before the reduction and reoxidation the surface treated particles of hydrated oxide of iron are tempered at a temperature of about 600.degree. to 900.degree. C.

Coating iron oxide particles for magnetic recording

A process for increasing the color purity of iron oxide pigment particles admixed with color-modifying impurities and obtained by the Penniman process or the aniline process, comprising introducing the particles into a magnetic field, and removing from the magnetic field two fractions of different magnetizability, the first fraction being iron oxide pigment particles of increased color purity and the second fraction being enriched in impurities.

Magnetic separation to improve purity of iron oxide pigments

A process for the oxidative dissociation of chrome-containing ores comprising agglomerating a mixture of a chrome-containing ore, an alkaline substance and a moist solid residue from a preceding operation as a leaning agent, dissociating the agglomerate and then leaching to form a solution of chromate and a solid residue, and separating said solution from said solid residue still wet with said solution. Advantageously the alkaline substance comprises sodium hydroxide or sodium carbonate, the still wet residue is added in such a quantity that the agglomerates obtained have a moisture content of between about 10 and 15% by weight, and at least about 70% by weight of the agglomerates have a diameter from about 0.1 to 3 mm.

Process for the oxidative dissociation of chrome-containing ores

In the production of iron oxide pigments and substantially iron-free sodium sulphate from iron sulphate by passing an oxygen-containing gas through an alkalized iron sulphate-containing solution at a temperature of about 40.degree. to 100.degree. C., and separating iron oxide pigment formed from the solids-free sodium sulphate-containing solution, the improvement of which comprises crystallizing out part of the sodium sulphate from the solids-free solution in a first crystallization step, separating the crystals from the sodium sulphate-containing mother liquor, dividing the mother liquor into first and second portions, dissolving solid iron sulphate hydrate in the first portion, adding to the second portion sodium hydroxide thereby to crystallize additional sodium sulphate, separating the additional crystals of sodium sulphate from the rest of the mother liquor, and using the rest of the mother liquor containing sodium sulphate and sodium hydroxide to alkalize further iron sulphate solution in the precipitation of further iron oxide pigment.

Production of iron oxide pigments and sodium sulphate

An acicular to prismatic ferrimagnetic iron oxide pigment with a porosity of less than about 10% by volume, and optionally containing up to about 15% by weight of other metal oxides such as Zn or especially Co, are produced by heating a suspension of iron(III)oxide hydroxide in an autoclave to a temperature above about 100.degree. C in the presence of at least one mono-, di- or tri-saccharide, at least one alkali metal or alkaline earth metal hydroxide or carbonate and excess water, and washing, filtering and drying the resulting pigments.

Hydrothermal process for producing dense iron oxide pigments

In a two-stage process for producing black iron oxide pigments wherein an iron salt solution is alkalized in a first stage to precipitate about 55 to 70% of the iron, the solution is oxidized to convert the precipitate to goethite, the solution is further alkalized in a second stage to precipitate the balance of the iron, the precipitated iron II hydroxide is allowed to react with goethite to form magnetite, the improvement which comprises effecting the second stage in the presence of an inorganic ionic compound of at least one metal selected from the group consisting of copper, nickel, aluminum, chromium, titanium, zirconium and vanadium in about 0.05 to 5% calculated as metal based on the weight of the final pigment. The resulting pigment is of high color intensity, narrow grain distribution range and pronounced magnetite structure.

Production of black iron oxide pigments

An acicular, magnetic iron oxide pigment containing about 0.05 to 5% by weight of an organo silicon compound is produced by treating iron oxide hydroxide seeds either dry or in suspension with an organo silicon compound. Preferred organo silicon compounds comprise polymethylphenylsiloxane, polydimethylsiloxane and polydiphenylsiloxane. Trivalent metal ions may subsequently be deposited. The resulting pigments show only minimal losses of coercive force during processing into magnetic tapes.

Growing community of inventors

Meerbusch, Germany

Ingo Pflugmacher