Montedison S.p.a.

Elio Gallinotti

Giampiero Basile

Giancarlo Boero

Pierfrancesco Aspes

Ugo Montiglio

The present invention concerns a stabilized ferromagnetic chromium dioxide and a process for obtaining the same. More particularly, the present invention relates to ferromagnetic chromium dioxide stabilized by means of the coating of its particles with a stabilizing substance, characterized in that the stabilizing substance is selected from the group consisting of a zinc, aluminum or chromium (III) polyphosphates having a high molar ratio phosphorus/metal and having, depending on the metal, the following formula: P.sub.2 O.sub.5.nZnO.mH.sub.2 O wherein 'n' in general is comprised between 0.286 and 0.667 while 'm' is generally comprised between 0 and 2.570; P.sub.2 o.sub.5.nAl.sub.2 O.sub.3.mH.sub.2 O wherein 'n' is in general comprised between 0.225 and 0.500, while 'm' is generally comprised between 0 and 2.68; P.sub.2 o.sub.5.nCr.sub.2 O.sub.3.mH.sub.2 O wherein 'n' is in general comprised between 0.143 and 0.333, while 'm' is generally comprised between 0.002 and 2.46.

Stabilized ferromagnetic chromium dioxide and process for its preparation

Ferromagnetic chromium dioxide is prepared by thermally decomposing, at a temperature of 250.degree.-500.degree.C, and a pressure of at least 80 atmospheres, a mixture of hydrated trivalent chromium chromate of the formula Cr.sub.2 (CrO.sub.4).sub.3.nH.sub.2 O, wherein n is 7-12, and antimony or a compound thereof, the amount of antimony in the mixture being between 0.2 and 1.8% by weight based on the weight of anhydrous Cr.sub.2 (CrO.sub.4).sub.3. In another embodiment, other known modifiers for chromium dioxide, such as lanthanum, lithium, strontium, iron or lead, or a compound thereof may be added to the mixture of chromium chromate and antimony. The amount of said other modifiers is between 0.1 and 2% by weight of the element, based on the weight of anhydrous Cr.sub. 2 (CrO.sub.4).sub.3.

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Alessandria, Italy

Elio Gallinotti