Preparation, microstructure and electrorheological property of nano-sized TiO₂ particle materials doped with metal oxides

New nano-sized TiO₂ electrorheological (ER) materials doped with different metal (M = Na, Zr, Ce, Al, Ca, Zn) oxides have been prepared. Relationships between the composition, microstructure, conductivity, dielectric property and ER effect of these materials have been studied. The results show that doping Na₂O, ZrO₂, Al₂O₃ or CeO₂ can enhance the ER performance of the TiO₂ material, whereas, doping CaO or ZnO would decrease the ER activity of the material. The shear stress (τ_E) of the suspension (25 wt%) of Na-doped TiO ₂ in dimethyl silicone oil reaches 1.6 kPa at the electric field strength E = 4.2 kV/mm and shear rate γ = 300 s^-1, and its τ_r value of 54.6 (τ_r = τ_E/ τ₀, where τ₀ is the shear stress at no electric field) is seven times higher than that of pure TiO₂ suspension. This high τ_r value is very advantageous to the use. The dielectric loss tangent (tanδ) plays a dominant role in influencing the ER performance of a particle material, and the effect of the surface area (pore volume, especially) and grain size should be taken into account.