Method for the preparation of fine hexagonal ferrite powders, in particular, for magnetic recording

Claim 3

Method as in claim 1 wherein the soluble compound of titanium is titanium trichloride (TiCl 3 ).

Claim 4

Method as in claim 1 wherein the alkaline earth metal (Re) is strontium and/or barium and the soluble compounds of such metals are carbonates and/or oxides.

Claim 5

Method as in claim 1 wherein the soluble compounds of cobalt are neutral or base carbonates and/or oxides.

Claim 6

Method as in claim 1 wherein the excess of citric acid over iron is 10 moles to 1 approximately.

Claim 7

Method as in claim 1 wherein preparation of the ferric citrate solution comprises the following steps: solution of nitrate of iron in distilled water and precipitation of ferrous hydroxide with an excess of concentrate ammonia; separation of the precipitate and washing of same until neutral pH is obtained; addition of a 1:2 mol solution of citric acid in water.

Claim 8

Method as in claim 5 wherein the solution of ferric citrate is pre-heated to between 60° and 70° C. approx until the precipitate is totally dissolved.

Claim 9

Method as in claim 1 wherein hydrogen peroxide is added to the solution prior to the first application of heat.

Claim 10

Method as in claim 1 wherein the soluble compound of a divalent transition metal is added to the solution of ferric citrate in water.

Claim 11

Method as in claim 1 wherein the inorganic residue is ground prior to the final application of heat.

Claim 12

Method as in claim 1 comprising the following steps: solution of nitrate of iron in distilled water and precipitation of ferrous hydroxide with an excess of concentrate ammonia; separation of the precipitate and washing of same until neutral pH is obtained; addition of a 1:2 mol solution of citric acid in water such that acid moles outnumber iron moles by approximately 10 to 1; preliminary application of heat at 60° . . . 70° C. approx until the precipitate is totally dissolved; addition of a carbonate of barium and/or strontium in stoichiometric proportion determined by the stoichiometry of the end-product; addition of carbonate of cobalt in stoichiometric proportion determined by the stoichiometry of the end-product; addition of titanium trichloride in stoichiometric proportion determined by the stoichiometry of the end-product; addition of hydrogen peroxide; a first application of heat at below 100° C. by means of which to eliminate excess hydrogen peroxide and carbon dioxide produced by decomposition of carbonates; addition of ethylene glycol in a proportion of 10% by volume (approx) of the solution with the resultant formation of organic macromolecules having chemically bonded inorganic ions; a second application of heat to bring about total dehydration and resultant formation of a solidified mass possessing the same cationic composition and the same chemical uniformity as the original solution; a third application of heat at between 400° . . . 450° C., bringing about total elimination of the organic part of the solidified mass, so as to leave an inorganic residue; grinding of the inorganic residue; and a final application of heat by means of which to induce crystallization of the hexaferrite.