Abstract: A process for the preparation of cobalt-containing isotropic magnetic iron oxides which are based on gamma-iron(III) oxide, contain from 2 to 7% by weight of cobalt(II) ions and less than 2% by weight of Fe(II) ions, the percentages in each case being based on the iron oxide, and have a particle length of from 0.08 to 0.30 .mu.m, a length/width ratio of from 1.5 to 3.5:1 and a specific remanent magnetization after saturation of not less than 60 nTm.sup.3 /g.

Abstract: The preparation of acicular ferrimagnetic iron oxides which contain cobalt and phosphate ions and, if desired, further additives, and their use for manufacturing magnetic recording media.

Abstract: Acicular metal particles consisting essentially of iron are prepared by reducing .alpha.-iron(III) oxide obtained--by dehydration--from acicular iron(III) oxide hydroxide prepared in the presence of phosphate ions and having a shape-stabilizing surface coating.

Abstract: A process for the preparation of acicular ferrimagnetic iron oxides by reducing gamma-iron(III) oxide hydroxide to magnetite, at from 280.degree. to 620.degree. C., by means of an organic compound which is decomposable at this temperature in the presence of iron oxide, and, optionally, a stream of reducing gas, and, if desired, then oxidizing the magnetite with oxygen-containing gases, at from 150.degree. to 450.degree. C., to acicular ferrimagnetic iron oxide of the formula FeO.sub.x, where x is from above 1.33 to 1.50, wherein the organic compound used for the reduction is a non-polar glycerol ester of a fatty acid which is introduced into the aqueous reaction suspension during the preparation of the gamma-iron(III) oxide hydroxide.

Abstract: A process for the manufacture of acicular ferrimagnetic iron oxide by converting acicular iron(III) oxide hydroxide at from 300.degree. to 650.degree. C., by treatment with an organic compound which decomposes in this temperature range in the presence of iron oxide, the iron(III) oxide hydroxide used for the reaction being a lepidocrocite which has been heat-treated at from 300.degree. to 700.degree. C.

Abstract: A modified acicular ferrimagnetic iron oxide which consists of a core of gamma-iron(III) oxide and a surrounding shell of gamma-iron(III) oxide modified by tin dioxide and carbon, and a process for its preparation.

Abstract: Acicular ferrimagnetic iron oxides are prepared by a process in which iron (III) oxide hydroxide consisting essentially of lepidocrocite is reduced at from 350.degree. to 600.degree. C. by means of an organic compound which is a synthetic polymer with a molecular weight of from 3,000 to 40,000 to give magnetite, which, if desired, is subsequently partially or completely oxidized with an oxygen-containing gas at from 200.degree. to 450.degree. C.

Abstract: A process for the preparation of acicular gamma-iron(III) oxide of high coercive force by reducing acicular iron(III) oxide hydroxide, as it is being passed continuously through a furnace having two or more heating zones at from 190.degree. to 700.degree. C., by means of a gas mixture which is produced by passing a stream of inert gas, heated to above 250.degree. C., through an organic substance also heated to above 250.degree. C. in a vessel, and, on introduction into the furnace, is first brought into contact with the .alpha.-iron(III) oxide formed from the iron(III) oxide hydroxide by elimination of water in the first heating zone of the furnace at from 190.degree. to 250.degree. C., the .alpha.-iron(III) oxide thereby being converted to magnetite which is subsequently oxidized with an oxygen-containing gas at from 150.degree. to 400.degree. C., to give gamma-iron(III) oxide.

Abstract: The invention relates to magnetic recording media comprising a non-magnetic base and, applied thereto, a firmly adhering magnetic coating based on a finely divided magnetic pigment and a special binder mixture. This binder mixture consists essentially of 20 to 90 percent by weight of an elastomeric polyurethane which is soluble in a volatile organic solvent, is practically free of isocyanate groups and has been obtained from a linear, aliphatic polyester or polyether and a diisocyanate of 6 to 24 carbon atoms, and of 10 to 80 percent by weight of a vinyl chloride copolymer which contains 50 to 90 percent by weight of vinyl chloride units and 10 to 50 percent by weight of units of one or more diesters of maleic acid with an alcohol of 1 to 3 carbon atoms, or of the reaction product of this binder mixture with a polyisocyanate of 6 to 50 carbon atoms.

Abstract: A process for the manufacture of ferromagnetic chromium dioxide modified with foreign elements, by reacting oxides of trivalent and hexavalent chromium under superatmospheric pressure at an elevated temperature in the presence of water and of antimony(III) oxide as modifier, with or without other modifiers in an amount not exceeding 15% by weight, wherein the antimony(III) oxide employed as modifier is, to the extent of more than one-third, present as the senarmontite cubic modification, has a specific surface area, measured by the BET method, of from 1.5 to 15 m.sup.2 /g, and is added in a total amount of up to 0.5% by weight, based on the resulting chromium dioxide.

Abstract: A process for the manufacture of acicular magnetic iron oxide consisting of a core of gamma-iron(III) oxide and a ferrite shell which contains, based on the total amount of magnetic material, from 0.2 to 12 percent by weight of cobalt(II) ions and from 0.1 to 15 percent by weight of iron(II) ions, wherein a solution containing cobalt(II) hydroxide and iron(II) hydroxide is applied to acicular gamma-iron(III) oxide particles and the latter are heated at 100.degree.-220.degree. C.

Abstract: Magnetic recording media, the magnetic coating of which consists of a dispersion of elongated ferromagnetic chromium dioxide particles in an organic binder, the dispersions exhibiting particularly good storage stability. This is achieved by admixing 0.5 to 6% by weight, based on the amount of chromium dioxide pigment, of the zinc salt of an aliphatic carboxylic acid of 8 to 18 carbon atoms, during the manufacture of the chromium dioxide dispersions. Chromium dioxide dispersions with good storage stability and a high degree of orientation of the elongated magnetic particles in the magnetic coating are thus obtained in a simple manner.

Abstract: Goethite is obtained by reacting an aqueous solution of an iron (II) salt with an aqueous solution of an alkali metal hydroxide and oxidizing the resulting iron(II) hydroxide. The oxidation is carried out in three stages. In the first stage, from 4 to 15% by weight are oxidized in the course of from 0.4 to 5 hours, in the second stage from 60 to 85% by weight are oxidized in the course of from 1.5 to 6 hours and in a third stage the remaining amount of iron is oxidized.

Abstract: Acicular .gamma.-iron(III) oxide is manufactured by reacting an iron(II) salt solution with aqueous solutions of alkali metal hydroxides and oxidizing the resulting suspension of iron(II) hyroxides in 3 stages. In the first stage not more than 8 percent by weight of the iron(II) hydroxide originally present is oxidized over a period of 0.5 to 4 hours, in the second stage from 25 to 55 percent by weight over a period of 1.5 to 6 hours and the remainder thereof in a third stage. Following this oxidation, the goethite formed is reduced to magnetite, which is then oxidized to acicular .gamma.-iron(III) oxide.

Abstract: Acicular gamma-iron(III) oxide is manufactured by reacting an iron(II) salt solution with an aqueous solution of an alkali metal hydroxide and oxidizing the resulting suspension of iron(II) hydroxide in three stages. In a first stage, at most from 0.1 to 4% by weight of the amount of iron(II) hydroxide originally present is oxidized in the course of from 0.1 to 4 hours, in a second stage from 10 to 25% by weight of the said original amount are oxidized in the course of from 1.5 to 6 hours and in a third stage the remaining amount is oxidized. After the oxidation, the goethite formed is reduced to magnetite and the latter is then oxidized to acicular gamma-iron(III) oxide.

Abstract: The invention relates to magnetic recording media comprising a non-magnetic base and, applied thereto, a firmly adhering magnetic coating based on a finely divided magnetic pigment dispersed in a binder which contains at least 50 percent by weight of a special polyurethane elastomer.This polyurethane elastomer is a thermoplastic polyurethane which is soluble in tetrahydrofuran and free from isocyanate groups, and which has been manufactured from (A) 1 mole of one or more hydroxyl-containing polyesters and/or hydroxyl-containing polyethers of molecular weight from 600 to 4,000, (B) from 3.5 to 15 moles of a branched-chain aliphatic diol of 4 to 10 carbon atoms or a mixture of aliphatic diols of 2 to 10 carbon atoms, of which at least 50 mole percent is a branched-chain aliphatic diol of 4 to 10 carbon atoms, (C) from 0 to 1 mole, but not more than 15 mole percent of the aliphatic diols according to B, of an aliphatic polyol with from 3 to 6 OH groups and 3 to 18 carbon atoms, and (D) from 4.

Abstract: Thermoplastic, elastic polyurethanes which are soluble in ethers and/or ketones and have a high surface hardness and high modulus of elasticity are manufactured from a polyester-ol and/or a polyether-ol, a substituted or unsubstituted diisocyanato-diphenylmethane or diisocyanato-diphenylsulfone, an aliphatic, branched-chain diol of the formula HOCH.sub.2 --CR.sup.1 R.sup.2 --CO.sub.2 OH, in which R.sup.1 is alkyl and R.sup.2 is alkyl or hydrogen, and, optionally, a triol.