Synthesis of spherical zirconia by precipitation between two water/oil emulsions

Microparticles of ZrO2 are produced by using precipitation method between two emulsion solutions. First, two solutions of stable reverse emulsion (water-in-oil) are prepared and mixed to form gelled precipitates, using normal heptane as the continuous oil phase and aqueous solutions of zirconium oxyacetate and aqueous ammonia as the suspending droplets. Through a series of operations, including distillation, filtration and washing, the dried precursors are obtained. After calcining the precursors at 750 degrees C, ZrO2 powder with a tetragonal structure is obtained. Principle factors that influence the emulsion stability, which subsequently affects the morphology and particle size of ZrO2 powder, are investigated, including the type and concentration of surfactant, volume ratio of water/oil, concentration of solute in water phases, and mixing intensity and time for emulsion formation. Four kinds of anionic surfactants are put to test for emulsion stability, among them Span 40 and Span 80 are considered as suitable surfactants for producing spherical micro-particles of ZrO2, which has a size range from several hundred nanometers to micrometers depending on the synthesis conditions. (C) 1999 Elsevier Science Limited. All rights reserved.