Soft solution preparation methods in a ZrO2–Al2O3 binary system

Two types of soft solution preparation methods were investigated for the production of zirconia in the presence of alumina or yttria from mixed aqueous solution of zirconyl chloride and aluminum or yttrium chloride. Tetragonal zirconia powder was obtained below 1000 °C by firing the mixed solution gel, which was prepared by adding citric acid. The particle size distribution was much narrower than the product obtained by a conventional coprecipitation method. For the second method, microgravity was applied for 4.5 s to the freezing of the mixed chloride aqueous solution. The precipitates were freeze-dried and then fired to 1000 °C in TG-DTA. The dried precipitates showed good crystallinity and homogenous mixing of the metal salts when the freezing of aqueous solution was started under microgravity. The main crystalline phase after firing was tetragonal ZrO2 due to a homogenous doping of Y2O3 and a homogenous dispersion of Al2O3, respectively.