The Rare-earth-doped Titanium Dioxide And Barium Titanate Electrorheological Behavior

In this paper, we propose a novel way to improve electrorheological (ER) effect by doping. The effect of rare earth doping on ER behaviors of two kinds of ciystal materials, titanium dioxide (Ti02) and barium titanate (BaTiO3), with large dielectric constant but weak ER activity, has been investigated in detail. The experimental results are given as follows: 1. The ER materials of anatase doped Ti02 with lanthanum or cerium ions were obtained by means of Sol-gel technique. Experiments show that doping of La, Ce into Ti02 is found to greatly improve the electrorheological effect and broaden the operational temperature range. Especially, substitution of 7-14mol% of the dopant for Ti is accompanied by relatively high shear stress t =7.4kPa (at 4kv/mm), which is 10 times larger than that of pure Ti02 ER fluid. The measurement of dielectric and conduction properties indicates that doping of rare earth leads to a large increase in dielectric loss, conductivity and dielectric constant of Ti02 ER fluid. These results can well explain the change of ER behaviors of Ti02. Furthermore, the effect of rare earth substitution on rheological and dielectric properties is discussed on the basis of the lattice distortion and defects in ciystal Ti02 originated from doping of rare earth. 2. The temperature dependence of Ti02 ER fluid was optimized by doping of rare earth. The ideal RE-doped Ti02 ER fluid exhibits the highest shear stress at 80 0C, but 40 0C for pure Ti02 ER fluid. Their different dielectric and conduction properties varying with temperature were discussed according to the thermally activated orientation or relaxation polarization and space-charge polarization, which arise from the lattice distortion, defect in crystal due to large- radius ions substitution for Ti4. 3. The ER fluids composed of RE (Y, La, Ce)-doped BaTiO3 were prepared by a modified Sd- gel means. Its ideal yield stress under DC field is about 3.2kPa, which is 10 times lager than that of pure BaTiO3 ER fluid. Worthy of note is that the ER effect bears obvious dependence on the type and content of rare earth ions. The ER activity increases with the doping content and reaches a maximum at i5mol% Y, (l0-5)mol% La, and 5mol% Ce, respectively. While the doping content remains fixed, the ER effect decreases with the radius of rare earth ions. XRD analysis verified the lattice distortion of the crystal, which is responsible for the improvement of its ER activity. 4. In the micro-emulsion system of H20/Span or DBS/n-amyl alcohollxylene, the particles of Ti02 coated with surfactants were obtained. The content of coated surfactants has a strong influence on ER behaviors. Proper coating of surfactants could increase the ER activity of Ti02. In addition, because R=[H20]/[Surfactant] could control the granularity of particles and the content of coated surfactants, the sedimentation stability could be controlled and improved to a large extent.