Preparation of microspheres from an alumina-zirconia sol

A sol-gel process produced microsphere of Al2O3 containing 10 wt% ZrO2 by coprecipitating Al and Zr hydroxides from the respective chlorides through the addition of NH4OH. In this paper, gel processing is examined as a function of temperature, pH, and residual Cl- content. The washed gel was peptized at 80°C with HCl and the sol concentrated to an Al3+ ion content of 4 mol/L. The concentrated sol is used to feed a pilot plant for microsphere production. The microspheres calcined at 1200°C are dense, with an average size of 20 μm and a BET surface area of 30 m2/g.