AN ULTRAFINE BARIUM FERRITE POWDER OF HIGH COERCIVITY FROM WATER-IN-OIL MICROEMULSION

An ultrafine barium ferrite powder of high coercivity and high saturat ion magnetization has been successfully prepared from an inverse water -in-oil microemulsion consisting of cyclohexane, NP5/NP9, and an aqueo us solution of mixed ferric nitrate and barium nitrate. An ammonium hy droxide solution was used as the precipitant to obtain the hydroxide p recursor of particle size in the range of 10-30 nm from the microemuls ion. The resulting precursor is characterized using techniques such as thermogravimetric analysis (TGA), differential thermal analysis (DTA) and a FT-IR analyzer. It was then calcined at various temperatures ra nging from 600 to 950 degrees C in order to develop the designed bariu m ferrite phase. Phase development in the precursor at each calcinatio n temperature was monitored using X-ray diffractometer and a Fe-57-Mos sbauer spectrometer analyzer. The particle size and size distribution of the calcined powders were determined using light scattering techniq ue, scanning electron microscope and a transmission electron microscop e. A high purity barium ferrite was obtained when the precursor was ca lcined at 950 degrees C for 4 h. It exhibits an intrinsic coercivity ( H-i(c)) of 5639 Oe and a saturation magnetization (M-s) of 69.7 emu/g, when characterized using a vibrating sample magnetometer (VSM). (C) 1 998 Elsevier Science B.V. All rights reserved.