SOL-GEL PREPARATION AND ELECTRORHEOLOGICAL ACTIVITY OF SIO2-TIO2 COMPOSITE POWDERS

The SiO2-TiO2 composite powders with various Si/Ti ratios were prepare d by the sol-gel processing, using tetraisopropylorthotitane (Ti(OPri) (4)) and tetraethoxysilane (Si(OEt)(4)) as starting materials. The eff ect of the powder's heat history on the electrorheological (ER) activi ty of the resulting suspensions, which were prepared by dispersing the powders into silicon oil, was investigated. The infrared spectra, sca nning electron microscopy, X-ray diffraction, and zeta potential were used to characterize the structural evolution of the as-prepared gel p owders upon heating. The results show a remarkable reduction in gelati on 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 n ucleophilic attack of the Ti atom by the as-hydrolyzed species of Si p recursor to form an environment similar to alkali catalysis. It was fo und that gel powders would gradually eliminate the -OH groups and beco me denser in structure upon heating, leading to a decrease of ER activ ity of the resulting suspensions. However, the initial Si/Ti composite compositions have little effect on ER activity behavior. (C) 1997 Aca demic Press.