Montedison S.p.a.

Ariello Rolando Corradi

Franco Montino

Giuliano Fagherazzi

Erminio Nonato

A process is disclosed for obtaining acicular magnetic particles of .gamma.-Fe.sub.2 O.sub.3 modified with Fe.sup.++ and Co.sup.++ ions. The product thus obtained and magnetic tapes containing said product are also disclosed. A suspension of acicular .gamma.-Fe.sub.2 O.sub.3 in an aqueous solution of soluble Fe.sup.++ and Co.sup.++ salts is prepared. NH.sub.3 is then added in such quantity that the molar ratio

Process for the preparation of magnetic powders based on .gamma.-Fe.sub.2

A process is disclosed for preparing metallic powders based on iron and suitable for magnetic recording, starting from acicular particles of an iron compound selected from the class consisting of .alpha.-Fe.sub.2 O.sub.3, .alpha.-FeOOH and Fe.sub.3 O.sub.4, by reduction with a gas containing more than 50% by volume of hydrogen, characterized in that the particles of the iron compound are treated with titanium, in the form of TiO(OH).sub.2 or TiO.sub.2, and with tin, in the form of Sn(OH).sub.2 or SnO(OH).sub.2 ; after which they are subjected to at least a heat treatment in air at 400.degree.-550.degree. C; and finally to a reducing treatment at 340.degree.-420.degree. C. The titanium is employed in an amount of 0.5-1% by weight, calculated as TiO.sub.2, and the tin in an amount of 3-6% by weight, based on pure iron. Prior to reduction, the particles of the iron compound may be treated not only with titanium and tin, but also with cobalt and/or silica, the cobalt in an amount not exceeding 6% by weight with respect to pure iron and the silica in an amount not exceeding 5% by weight with respect to pure iron. The metallic powders based on iron suitable for magnetic recording, and containing 0.5-1% by weight, with respect to pure iron, of titanium calculated as TiO.sub.2, and 3-6% by weight of Sn, with respect to pure iron, and having an average particle length ranging from 0.3 to 1.mu. and an average particle diameter ranging from 0.1 to 0.4 .mu.; with or without a maximum of not more than 5% by weight of SiO.sub.2 with respect to pure iron and not more than 6% by weight of Co with respect to pure iron, are also disclosed.

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Romentino (Novara), Italy

Ariello Rolando Corradi