US 4,071,610 AGranted

Manufacture of gamma-iron(III) oxide

AssigneeBASF SE

InventorsEberhard Koester, Gerd Wunsch, Eduard Schoenafinger, Hans Henning Schneehage

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Abstract

A process for the manufacture of acicular gamma-iron(III) oxide, in which the non-magnetic, acicular iron(III) oxide is treated with a solution of a compound of the formula I ##STR1## where R.sup.1 and R.sup.2 are ##STR2## or O--R.sup.5, R.sup.3 is H, OH, ##STR3## or O--R.sup.5, R.sup.4 is alkyl or cycloalkyl of 1 to 16 carbon atoms and the R.sup.4 's may be identical or different, and R.sup.5 is alkyl, cycloalkyl or aralkyl of 3 to 18 carbon atoms, and is then converted to gamma-iron(III) oxide by reduction to magnetite, followed by oxidation. The gamma-iron(III) oxide obtained is distinguished by a high coercive force and improved magnetic orientation when used as a magnetic pigment for the manufacture of magnetic recording media.

Claims2

Dependent claims

A process for the manufacture of acicular gamma-iron(III) oxide of high coercive force and giving improved orientation, which comprises the steps of

a. mixing a suspension of non-magnetic, acicular alpha-FeOOH with a solution of a compound of the formula I ##STR7## where R.sup.1 and R.sup.2 are ##STR8## or O--R.sup.5, R.sup.3 is H, OH, ##STR9## or O--R.sup.5, R.sup.4 is alkyl or cycloalkyl of 1 to 16 carbon atoms and the R.sup.4 's may be identical or different, and R.sup.5 is alkyl, cycloalkyl or aralkyl of 3 to 18 carbon atoms, in water or alcohols of 1 to 4 carbon atoms, and then removing the solvent, the amount of said compound I being from about 0.5 to 10 percent by weight based on said non-magnetic iron oxide,
b. reducing the material, obtained according to (a), by means of gases containing hydrogen, at from b 350.degree. to 600.degree. C, to give magnetite, and
c. oxidizing the magnetite, by means of gases containing oxygen, at from 200.degree. to 450.degree. C, to give gamma-iron(III) oxide.

Dependencies are inferred from the claim text.