The preparation of ultrafine particles (particles of sizes in the nanometre range) is one of the most i mportant challenges of the new technologies [ I ]. A variety of methods has been proposed for obtaining ultrafine particles, which include precipitation in aqueous and organic media, thermal decomposition, hydrothermal synthesis and cryochemical processing. Recently, compartmentalized liquids such as micro-emulsion [2], vesicle [3] and liquid crystals [4] have been used successfully to prepare ultrafine particles. These compartmentalized liquids offer the advantage of reducing the reaction vessel to the size of the particles. In water/oil (w/o) micro-emulsions, for example, the aqueous phase is dispersed as nanosized droplets surrounded by oil (continuous phase). KTa-noparticl.es of metals, metal borides, sulphides and oxides [5] have been synthesized in a simple and convenient manner by using w/o micro-emulsions as reaction media. However, low yield and high cost due to the use of a large amount of surfactant to prepare the micro-emulsion have hindered the industrial application of the micro-emulsion method. On. the other hand, conventional emulsion precipita-tion offers an alternative method for preparing particles with spherical morphologies and submicro-metxe size by using a relatively small amount of surfactant as emulsifier [6, 7]. In the work reported here, a new method of preparing nanosized ZnS particles in conventional w/o emulsions by using microwave heating was developed.
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