METHOD OF PRODUCING PERMANENT MAGNET FROM STRONTIUM HEXAFERRITE POWDER Russian patent published in 2011 - IPC B22F3/87 H01F1/36 

FIELD: process engineering.

SUBSTANCE: invention relates to powder metallurgy, particularly, to materials intended for production of permanent magnets. Strontium hexaferrite powder is synthesized from aqueous solutions of individual sulphates in stoichiometric ratio corresponding to final product, i.e. phase SrFe₁₂O₁₉. To increase content of phase SrFe₁₂O₁₉ additives are introduced in the following concentrations: CaCO₃-1.2%, SiO₂-0.25% and H₃BO₃-0.3% or CaCO₃-0.75%, SiO₂-0.3% and H₃BO₃-0.35%. Mixed solution is dispersed and frozen by liquid commercial nitrogen while produced granules are subjected to sublimation dewatering at 1.5 Pa and 230 K in drying start and 363 K at drying finish to obtain salt product. Salt product is subjected to thermal decomposition at 1200-1220 °C for 4 hours to produce ferrite powder by ferritising oxides formed. Impurities are extracted from powder by treatment with distilled water and ultrasound at frequency of 20=25 kHz for 20 minutes. Powder is dried at 353-373 °C to residual moisture content of not over 2 wt %.Thereafter, compaction in magnetic field is carried out and sintering at 1100-1300 °C in tunnel furnace in jog mode.

EFFECT: higher coercive force and mechanical strength.