| 摘要 |
Novel hexaferrite compounds having the formula (I): AFe12-r-sMrNsO19 (I) 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, are prepared by (a) forming particles of a doped Fe3O4/ACO3 co-precipitate 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; (b) suspending the doped particles in a concentrated aqueous solution of a halide; (c) spray-drying the suspension to form a dried powder comprising doped Fe3O4/ACO3 particles distributed over the surfaces of the high-melting halide crystals; (d) calcining the dried powder at a temperature from about 700 DEG C to about 900 DEG C to convert the Fe3O4/ACO3 solids into doped barium hexaferrite particles having formula (I) and an average particle size from about 0.01 to about 0.3 micrometres; and (e) recovering the doped hexaferrite particles from the alkali halide. Doped co-precipitates mentioned in step (a) of formula BaCO3.(4-7y/6)Fe3O4.(3y/2)FeO.yTiO2.yCoO in which y is from 0.4 to 1.0 are novel and may be prepared by reacting together at a temperature of 40-120 DEG C in an aqueous medium containing effective amounts of ions of the two dopants, a ferric halide, a ferrous halide, a barium or strontium halide and an alkali metal carbonate.
|
