Sol-gel preparation and characterization of spherical ZrO2-SiO2 particles

Spherical zirconia/silica particles of 30-40 mu m average diameter, surface area of 500-700 m(2)/g and a pore volume > 0.5 cm(3)/g were prepared in the compositional range Zr less than or equal to 18 wt%, via emulsion-gelation of mixed sols. Thermal hydrolysis of zirconyl chloride followed by addition of tetraethylorthosilicate (TEOS) and hydrolysis of TEOS in the presence of zirconyl chloride solution in ethylene glycol (EG) have been compared. In the latter case, a more homogeneous morphology and composition was obtained, when the acidic sol was emulsified in decanol and gelled in a basic solution of cyclohexylamine in decanol. Thermal aging of mixed gels in alkaline mother liquor was found to strengthen the gel network during preparation. Also surface compositions, surface properties and crystallization kinetics were different. The better behavior of samples prepared in the presence of EG was attributed to the effect of EG (as complexing agent), favouring the co-precipitation of Si-containing and Zr-containing moieties. (C) 1998 Elsevier Science B.V.