Control of zirconia particle size by using two-emulsion precipitation technique

Zirconia powder is synthesized in two types of reverse emulsions, i.e., macroemulsion and microemulsion. In either of the systems, two solutions of reverse emulsion, one containing Zr⁴⁺ aqueous droplets and the other aqueous ammonia droplets, with the same water/oil (w/o) ratio are prepared separately and mixed together to form a slurry of ZrO₂ precursors. Then the precursors are recovered and calcined to form tetragonal ZrO₂. Factors that affect the emulsion stability and particle size are investigated, including type of oil, w/o ratio, type and concentration of surfactant, concentration of aqueous solutions, and mixing intensity. The difference in particle size and thus calcination temperature is significant between the zirconia crystals produced from the two different types of emulsions. Thus, coupling the macroemulsion and microemulsion precipitation processes, the mean size of spherical ZrO₂ particles ranging from tens of nanometers to a few micrometers can be controlled.