Basf Aktiengesellschaft

Rudolf Brodt

Manfred Ohlinger

Werner Steck

Eberhard Koester

Helmut Jakusch

Werner Loeser

Wilhelm Sarnecki

Christof Jaeckh

A process for the manufacture of acicular ferrimagnetic iron oxide by dehydrating acicular iron(III) oxide hydroxides to give acicular iron(III) oxides, then reducing these iron(III) oxides at from 300.degree. to 650.degree. C. by means of an organic compound which decomposes in this temperature range, and oxidizing the reduced product with an oxygen-containing gas at from 200.degree. to 500.degree. C., wherein the acicular iron(III) oxide hydroxides employed consist of a mixture of goethite and lepidocrocite, containing at least 60% of the latter, and the dehydration is carried out at from 250.degree. to 700.degree. C.

Manufacture of acicular, ferrimagnetic iron oxide

A process for the manufacture of acicular ferromagnetic iron particles by reducing acicular iron(III) oxide hydroxides which consist of pure synthetic lepidocrocite or a mixture of synthetic goethite and at least 70% by weight of synthetic lepidocrocite. The iron(III) oxide hydroxides used carry, on their surface, an alkaline earth metal cation and an anion of a monobasic, dibasic or tribasic aliphatic carboxylic acid of up to 6 carbon atoms or an organic compound containing at least two groups capable of chelating the alkaline earth metal cation, and are produced in such a way that they consist of at least 70 percent by weight of lepidocrocite and have a length-to-width ratio of not less than 15:1. Reduction of such iron(III) oxide hydroxides gives iron particles with pronounced shape anisotropy, which exhibit both good magnetic properties and a narrow field strength distribution.

Manufacture of acicular ferromagnetic iron particles

A process for the manufacture of acicular ferromagnetic metal particles which essentially consist of iron and carry, on their surface, from 0.02 to 0.6% by weight of boron in the form of a borate, by reducing an acicular iron oxide with a gaseous reducing agent at from 250.degree. to 500.degree. C., wherein a compound selected from the group comprising boron oxyacids and their inorganic salts is precipitated on the said iron oxide before reduction.

Manufacture of ferromagnetic metal particles essentially consisting of

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Weinheim, Germany

Rudolf Brodt