Study on formation of polymeric TiO₂-ZrO₂sols by small angle X-ray scattering

Metal oxide sols can be prepared from metal alkoxides M(OR)₄by hydrolyzation, which has been widely used in synthesis of nano-porous ceramic membranes by sol-gel method. Polymeric TiO₂-ZrO₂ sols were prepared by controlled hydrolyzation of the mixture of titanium isopropoxide and zirconium n-propoxidein isopropanol. The formation of TiO₂-ZrO₂ sols from the initial reactant mixtures with a molar ratio of Ti(i-OC₃H₇)₄: Zr(n-OC₃H₇)₄: H₂O: i-C₃H₇OH=0.9: 0.1: m: 30 (m=1.8, 2.0, 2.2) was investigated by small angle X-ray scattering (SAXS). The effects of the molar ratio of water to metal alkoxides H₂O/M(OR)₄ (M=Ti+Zr) in the initial reactant mixture, reaction temperature and Zr(n-OC₃H₇)₄ on formation of TiO₂-ZrO₂ sols were discussed. When the molar ratio ofH₂O/M(OR)₄=1.8, a few colloidal particlesform. When the molar ratio ofH₂O/M(OR)₄ is in the range of 2.0-2.2, the colloidal particles in TiO₂-ZrO₂ sols have a mass fractal structure with a fractal dimension of 1.2 ≤D_m< 1.4. As the molar ratio ofH₂O/M(OR)₄ increases from 2.0 to 2.2, the duration of colloidal particle formation becomes shorter, the size and fractal dimension of colloidal particles increase, and the stability of TiO₂-ZrO₂ sol decreases. Furthermore, the mixtureof [Ti(i-OC₃H₇)₄+Zr(n-OC₃H₇)₄] hydrolyzes faster than Ti(i-OC₃H₇)₄. TiO₂-ZrO₂ sol has lower stability than TiO₂ sol from the initial reactant mixtures with the same molar ratio of H₂O/M(OR)₄.