Preparation and Characterization of Coprecipitated Strontium Hexaferrite

Abstract

Strontium hexaferrite was prepared from coprecipitated strontium iron complex obtained from metal chloride solutions in the presence of ammonium carbonate. Coprecipitation parameters were varied in the ranges pH 7.5–10, dilution 0.001–0.5 moles Fe in solution and Fe/Sr ratio 11–25. X-ray diffraction indicated crystalline SrCO3 and amorphous hydroxide of iron in the precipitate. Transmission electron micrographs indicated decrease in particle size with decrease in concentration of Fe, (600 Å at 0.04M to 55 Å at 0.001M) and an increase with pH (400 Å at pH 7.0 to 840 Å at pH 9.0) when other variables were held constant. Lattice parameters of the hexaferrite showed c0 = 23.13 Å (23.05 Å) and a0 = 5.880 Å (5.885 Å) with published values in parentheses. Ferritization of powders was carried out in the range 1000°-1200°C after precalcination at 800°C. Magnetic studies indicated highest σs, the saturation moment at 61.3 emu.gm−1 for polycrystalline material (74.3 reported for single crystal) at room temperature for Fe/Sr ratio of 11 and the coercive, field iHc value of 4.2 kOe (6.5 kOe reported for polycrystalline powder) for Fe/Sr ratio of 23. A Curie temperature of 460°C (463°C reported) was obtained for Fe/Sr ratio 11 for the sample ferritized at 1100°C.