Bayer Aktiengesellschaft

Bernd Stephan

Franz Hund

Gunter Buxbaum

Gerhard Schroeder

Wilhelm Holznagel

A finely divided magnetite pigment such as is used in magnetic tapes is stabilized against oxidation by contact with a heterocyclic nitrogen compound such as morpholine, triazole, piperazine or substitution products thereof. The heterocyclic compound can be applied as a solution or in vapor form.

Stabilization of magnetite pigments with heterocyclic nitrogen compounds

An Fe.sub.3 O.sub.4 iron oxide black pigment having incorporated therein up to about 50 mole percent of .gamma.-Fe.sub.2 O.sub.3 plus Me Fe.sub.2 O.sub.4 (wherein Me is at least one of magnesium, manganese, cobalt, nickel, aluminum, chromium, titanium, copper, zinc and cadmium) having a specific surface according to BET of greater than about 12 m.sup.2 /g, up to about 10% by weight of a substantially insoluble inorganic compound as coating and a stability to oxidation with air under standardized conditions of greater than about 130.degree. C. Advantageously the coating comprises at least one of zinc hydroxide, zinc phosphate, zinc phosphite, aluminum phosphate and silica, being precipitated onto the suspended pigment from a solution. The resulting pigments are of improved resistance to oxidation, rendering them especially useful for pigmenting inorganic and organic dispersions and for use on magnetogram supports.

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Munich, Georgia

Bernd Stephan