Method of preparing a magnetic pigment of .gamma.-Fe.sub.2 O.sub

Details Method of preparing a magnetic pigment of .gamma.-Fe.sub.2 O.sub Method of preparing a magnetic pigment of .gamma.-Fe.sub.2 O.sub

1980-02-04

1984-01-10

Pianalto, Bernard D.

Stock material or miscellaneous articles

Composite

Of metal

252 6254, 423634, 428694, 428900, H01F 1002

Patent

active

044254091

ABSTRACT:
A method of manufacturing a magnetic pigment of .gamma.-Fe.sub.2 O.sub.3 particles in which the process starts with an alkaline or acid reacting aqueous dispersion of .gamma.-Fe.sub.2 O.sub.3. According to the invention, a water-soluble ammonium salt, which is derived from a low molecular weight, weakly acidic organic acid, is added to the aqueous dispersion, the .gamma.-Fe.sub.2 O.sub.3 particles flocculating. The flocculated .gamma.-Fe.sub.2 O.sub.3 is separated, washed with water which preferably also comprises such a water-soluable ammonium salt, and is then dried. The ammonium salt volatilizes in the drying process used either as such or after decomposition. A suitable ammonium salt is ammonium acetate. The pigment obtained according to the invention has a low content of salt absorbed at the surfaces of the pigment particles, for example, a content lower than 0.1 and, for example 0.03% by weight. A magnetic recording element which is based on the pigment obtained according to the invention shows an improved life time in particular upon storage or during use in moist environments.

REFERENCES:
patent: 4054643 (1977-10-01), Desmond
"Purification of Iron Oxide [Fe.sub.2 O.sub.3 ]", Mitani et al, Chemical Abstracts, vol. 82, p. 615 (1975), Abstract No. 148826n.

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