Sol-gel preparation and electrorheological activity of SiO2-TiO2 composite powders

The SiO2-TiO2 composite powders with various Si/Ti ratios were prepared by the sol-gel processing, using tetraisopropylorthotitane (Ti(OPri)(4)) and tetraethoxysilane (Si(OEt)(4)) as starting materials. The effect of the powder's heat history on the electrorheological (ER) activity of the resulting suspensions, which were prepared by dispersing the powders into silicon oil, was investigated. The infrared spectra, scanning electron microscopy, X-ray diffraction, and zeta potential were used to characterize the structural evolution of the as-prepared gel powders upon heating. The results show a remarkable reduction in gelation time, relative to the single-component systems, due to the combined effects of a higher reactivity of Ti(OPri)(4) over Si(OEt)(4) and a nucleophilic attack of the Ti atom by the as-hydrolyzed species of Si precursor to form an environment similar to alkali catalysis. It was found that gel powders would gradually eliminate the -OH groups and become denser in structure upon heating, leading to a decrease of ER activity of the resulting suspensions. However, the initial Si/Ti composite compositions have little effect on ER activity behavior. (C) 1997 Academic Press.