Electrorheological Behavior of Ni/(TiO_2+Urea)Core-shell Nano Particles

The Ni/(TiO2+Urea)core-shell nano particles composed of nano Ni particles and urea-doped TiO2 coating,were synthesized by using Sol-Gel method,and their electrorheological(ER) behaviors were investigated.The results show that ER activity of the particles are closely associated with heat-treatment temperature and urea content.The shear stress decreases when the particles is heat-treated above 320℃.When the mass ratio of urea to Ti is 30%,the shear stress of the ER fluid made from Ni/(TiO2+Urea) particles reaches 40kPa(the DC electric field is 4kV/mm),which is 10 times as high as that made from particles without urea.However,the shear stress decreases when excessive urea is added.The microstructure observation of the ER fluids under DC electric field shows that the particles aggregate to form thicker and dense column structure when the mass ratio of urea to Ti is 30%,while the column structure is broken when excessive urea(30%) is added.A thin and loose column structure is formed in ER fluid without urea added.It is suggested that the ER behaviors is substantially correlated with the polar molecules in urea.