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

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