Surface analyses of barium hexaferrite particles for magnetic suspensions

The stabilization of a suspension made from barium hexaferrite (BaHF), hard magnetic particles was studied. The magnetic attraction between the particles of BaHF was reduced by the adsorption of the surfactant dodeclybenzene sulphonic acid (DBSa) onto the particles' surfaces. With the adsorption of the surfactant, the electrostatic and steric repulsions between the particles were enhanced and stable suspensions were prepared from three different powders of BaHF, with particles sizes 5-20, 10-130 and 40-300 nm. The stability of the suspensions was determined with zeta-potential, saturation-concentration measurements, TEM and FTIR spectroscopy. The zeta-potential was increased with the addition of surfactants and the saturation concentration was increased with the decreased particle size. A stable suspension of the largest particles with a very high saturation concentration was prepared only by avoiding the application of an external magnetic field during the preparation of the suspension. The adsorption of the surfactant was observed in the FTIR spectra as a shift of the band assignment to the Fe-O vibrations. The red shift of the band by 37 or 53 cm(-1) appears with the adsorption of the DBSa, and a blue shift by 41 and 67 cm(-1) was observed, where two surfactants, DBSa and acetic acid, were used. The band shift is only partly observed in the suspension of the largest particles due to the effect of the particles' sizes. Copyright (C) 2010 John Wiley & Sons, Ltd.