Process for making selected doped barium and strontium hexaferrite particles

摘要

A process for preparing doped barium and strontium hexaferrite compounds having the formula (I): ##EQU1## wherein A is barium or strontium; M is cobalt, zinc, nickel; N is titanium or ruthenium and r and s are individually in the range from about 0.1 to about 1.2, said process comprising:PP(a) forming particles of a doped Fe. sub.3 O.sub.4 /ACO.sub.3 co-precipitate wherein A is defined above from (i) a ferric compound, (ii) a ferrous compound, (iii) a barium or strontium compound, (iv) a cobalt, zinc or nickel compound, (v) a titanium or ruthenium compound and (vi) alkali metal carbonate;P P(b) suspending the doped Fe.sub.3 O.sub.4 /ACO.sub.3 particles in a concentrated aqueous solution of an alkali halide;PP (c) spray drying said suspension to form a dried powder comprising said doped Fe.sub.3 O.sub.4 /ACO.sub.3 particles distributed onto the surfaces of the high temperature-melting alkali halide crystals;PP (d) calcining said dried powder at a temperature from about 700° C. to about 900° C. to convert said Fe.sub.3 O.sub.4 /ACO.sub.3 solids into doped barium hexaferrite particles having formula (I) and an average particle size from about 0.01 to about 0.3 microns; andP P (e) recovering said doped hexaferrite particles from said alkali halide.