Solid solutions of magnetic oxides and method of preparation

Claim 1

A method for the preparation of a metastable solid solution ferrite of defect spinel structure having vacancies, which is derived from mestastable iron sesquioxide γ-Fe 2 O 3 by substituting for some of the Fe 3+ ions and for some of the vacancies a divalent metal M taken from the group consisting of Zn, Mn, Ni, Cu, Mg and Cd, the solid solution being binary and having the formulation: (γ -Fe.sub.2 O.sub.3) .sub.1-x (M Fe.sub.2 O.sub.4)x 0.01 < x < 0.86 the method comprising the following steps:

Claim 2

A method for the preparation of a metastable solid solution ferrite of defect spinel structure having vacancies, which is derived from mestastable iron sesquioxide γ-Fe 2 O 3 by substituting for some of the Fe 3+ ions and for some of the vacancies a divalent metal M taken from the group consisting of Zn, Mn, Ni, Cu, Mg and Cd, the solid solution being binary and having the formulation: (γ -Fe.sub.2 O.sub.3) .sub.1-x (M Fe.sub.2 O.sub.4)x 0.01 < x < 0.86 the method comprising the following steps:

Claim 12

A method for the preparation of a metastable solid solution ferrite of defect spinel structure having vacancies, which is derived from metastable iron sesquioxide γ -Fe 2 O 3 by substituting for some of the Fe 3+ ions and for some of the vacancies more than one divalent metal M taken from the group consisting of Co, Zn, Mn, Ni, Cu, Mg and Cd, the solid solution having the formulation: (γ -Fe.sub.2 O.sub.3) .sub.1-(x+y+ . . .) (M Fe.sub.2 O.sub.4).sub.x (M'Fe.sub.2 O.sub.4).sub.y . . . 0.01 < (x+y+ . . .)< 0.86 the method comprising the following steps: (a) preparing by co-precipitation a water insoluble mixed oxalate containing Fe 2+ ions and divalent ions of more than one divalent metal of said group, said mixed oxalate corresponding to the formula: (Fe.sub.1-(u+v+ . . .).sup.2+ M.sub.u.sup.2+ M'hd v . . . .sup.2+) C.sub.2 O.sub.4, 2H.sub.2 O 0.005 < (u+v+. . .)< 0.30 where the value of u, v, . . . is such that the aggregate proportion of the divalent metals to iron in the said oxalate is the same as the proportion thereof in the said solid solution; (b) heating uniformly and progressively said mixed oxalate in an oxygen containing gas to a temperature selected from within the cross-hatched area of FIG. 2 according to the proportion of divalent metals to iron plus divalent metals, and continuing the heating step until said oxalate is decomposed and most of the resultant carbon is eliminated, this heating step being stopped before formation of rhombohedric oxide α-Fe 2 O 3 is effected; (c) heating the product of step (b) in a steam containing hydrogen atmosphere to produce a substituted magnetite formed of crystallites having an average size of more than 200 A and free from residual carbon and from metallic iron, the proportion of steam being between 7% and 90% by volume and the temperature being between 260° and 480° C, and the percentage of steam selected for inclusion in the hydrogen atmosphere increasing with said temperature; (d) and heating said substituted magnetite in an oxygen containing gas to oxidize same at a temperature selected from within the cross-hatched area of FIG. 4 according to the proportion of divalent metals to iron plus divalent metals, this heating step being stopped before formation of rhombohedric α- Fe 2 O 3 is effected.

Claim 13

A method for the preparation of a metastable solid solution ferrite of defect spinel structure having vacancies, which is derived from metastable iron sesquioxide γ -Fe 2 O 3 by substituting for some of the Fe 3+ ions and for some of the vacancies more than one divalent metal M taken from the group consisting of Co, Zn, Mn, Ni, Cu, Mg and Cd, the solid solution having the formulation: (γ -Fe.sub.2 O.sub.3) .sub.1-(x+y+ . . .) (M Fe.sub.2 O.sub.4).sub.x (M'Fe.sub.2 O.sub.4).sub.y . . . 0.01 < (x+y+ . . .)< 0.86 the method comprising the following steps: (a) preparing by co-precipitation a water insoluble mixed oxalate containing Fe 2+ ions and divalent ions of more than one divalent metal of said group, said mixed oxalate corresponding to the formula: (Fe.sub.1-(u+v+ . . .).sup.2+ M.sub.u.sup.2+ M'hd v . . . .sup.2+) C.sub.2 O.sub.4, 2H.sub.2 O 0.005 < (u+v+. . .)< 0.30 where the value of u, v, . . . is such that the aggregate proportion of the divalent metals to iron in the said oxalate is the same as the proportion thereof in the said solid solution; (b) heating uniformly and progressively said mixed oxalate in an oxygen containing gas to a temperature selected from within the cross-hatched area of FIG. 2 according to the proportion of divalent metals to iron plus divalent metals, and continuing the heating step until said oxalate is decomposed and most of the resultant carbon is eliminated, this heating step being stopped before formation of rhombohedric oxide α-Fe 2 O 3 is effected; (c) heating the product of step (b) in a steam containing hydrogen atmosphere to produce a substituted magnetite formed of crystallites having an average size of more than 200 A and free from residual carbon and from metallic iron, the proportion of steam being between 7% and 90% by volume and the temperature being between 260° and 480° C, and the percentage of steam selected for inclusion in the hydrogen atmosphere increasing with said temperature; (d) and heating said substituted magnetite in an oxygen containing gas to oxidize same at a temperature selected from within the cross-hatched area of FIG. 4 according to the proportion of divalent metals to iron plus divalent metals, this heating step being stopped before formation of rhombohedric α- Fe 2 O 3 is effected.