ena. It is well established that the particle nature can influ-The SiO 2 -TiO 2 composite powders with various Si/Ti ratios ence the ER activity of the resulting suspension; however, were prepared by the sol-gel processing, using tetraisopropylorthe research work on this aspect remains insufficient, espethotitane (Ti(OPr i ) 4 ) and tetraethoxysilane (Si(OEt) 4 ) as starting cially for the effect of the surface state and porous structure materials. The effect of the powder's heat history on the electroof particles on ER activity.
rheological (ER) activity of the resulting suspensions, which were
TiO 2 is a good solid material for ER fluid due to its high prepared by dispersing the powders into silicon oil, was investidielectric constant of around 80, but its semiconducting gated. The infrared spectra, scanning electron microscopy, X-ray property generally makes the resulting ER fluid broken when diffraction, and zeta potential were used to characterize the structhe resultant suspension is exposed to the external field. This tural evolution of the as-prepared gel powders upon heating. The results show a remarkable reduction in gelation time, relative to does not allow a wide use of this material in ER fluid. SiO 2 the single-component systems, due to the combined effects of a is an insulate material. The addition of SiO 2 into TiO 2 powhigher reactivity of Ti(OPr i ) 4 over Si(OEt) 4 and a nucleophilic der can increase the insulating property and thus prevent the attack of the Ti atom by the as-hydrolyzed species of Si precursor ER system from breaking.
to form an environment similar to alkali catalysis. It was found Sol-gel processing has been widely used to control the that gel powders would gradually eliminate the -OH groups and surface state and the porous structure of products (9, 10). become denser in structure upon heating, leading to a decrease of The preparations of single-component SiO 2 and TiO 2 films, ER activity of the resulting suspensions. However, the initial Si/ monoliths, and fibers have also been extensively reported; Ti composite compositions have little effect on ER activity behavhowever, the understanding of the chemical process of the ior.