Research Of Microemulsion Method Applied In Preparing Rodlike Particles

In this paper, rodlike precursor particles for barium ferrite and zinc oxide have been prepared by inverse microemulsion method. On sintering, rodlike barium ferrite particles and zinc oxide particles are yielded which might be applied in the manufacture of new magnetic materials and new dielectric materials.W/O microemulsion, commonly called inverse microemulsion, is a system composed of aqueous phase, oleic phase, surfactants as well as promoting surfactants. The inner aqueous core can serve as a micro reaction vessel inside which various reactions can be carried out. For example, precipitation can be undertaken in an inverse microemulsion, and the shape as well as the size of precipitate particles can be controlled through varying the microemulsion components. In this paper, a relatively stable microemulsion has been achieved; the conditions and mechanism of the growth of rodlike barium ferrite (BaFe12O19) and zinc oxide (ZnO) are investigated.Firstly, the inverse microemulsion consisting of isooctane, cetanyl trimethyl ammonium bromide (CTAB), n-C4H9OH and water with ammonia and ammonium oxalate as precipitants has been studied in different volume ratio of aqueous phase to oleic phase by means of phase graph. As a result, a stable microemulsion with relatively large aqueous capacity has been prepared.Secondly, a rodlike barium ferrite precursor with an average size of 0.72-19.6μm and aspect ratio of 2.6-8.3, respectively, has been successfully prepared by inverse microemulsion method. The influence of preparation conditions, such as the volume ratio of aqueous phase to oleic phase, the starting concentrations of metal ions, the starting concentration ratios of metal ions to precipitants, the starting ratio of Fe to Ba as well as reaction time, on the size, shape and constitutes of precursor particles has been extensively investigated.The rodlike precursor particles can be transformed into rodlike particles of barium ferrite on sintering at 780℃, which is much lower than conventional sintering temperature of 1240℃ at which the precursor sample prepared by coprecipitation method is transformed into barium ferrite particles.Finally, by carefully varying the volume ratio of aqueous phase to oleic phase, which is predominant in preparation conditions, rodlike zinc oxalate, rodlike zinc hydroxide and rodlike zinc carbonate particles have also been prepared in the same inverse microemulsion succeefully. As in the case of barium ferrite, these rodlike precursors can be transformed into rodlike zinc oxide particles with the size of 1.4-1.8 μm and aspect ratio of 9.0-9.2 on sintering at the temperature of 500℃.In conclusion, inverse microemulsion method is a feasible and economical process for praparing barium ferrite and zinc oxide rodlike particles.