Research Of Electrorheological Or Magnetorheological Fluid Of New Type Core-shell Nano Particles

Electrorheological or magnetorheological fluid (abbreviated EMR) is a suspension system formed by solid particles dispersed in insulating oil. When it is applied electric field or magnetic field, its viscosity, shear stress increases rapidly in the millisecond time, while the external field is removed, it can come back to liquid again in the millisecond time. This change is reversible and continuous, shows a good mechanical behavior of electronic control. It has broad application in the field of vehicles, hydraulic equipment, machinery manufacturing, sensor technology in the future. However, at present this kind of materials still can not meet the needs of engineering applications because of the problemes of low strength and easy-to-settlement.In this thesis, a new type core-shell nano-particles as the disperse phase of EMR is invented, the core/shell particles of Ni coated by TiO₂ doped by different additives were obtained by the sol-gel method, and the Electrorheological or Magnetorheological fluid behavior was investigated. The XRD and the FI-IR analysis showed that amorphous TiO₂ and functional group are coated in the face of Ni particle. The TEM morphology observation shows that particles have complete core-shell structure, which indicates that core-shell structure dissolving metal, ceramic and organic molecules is obtained. Electrorheological or Magnetorheological fluid behavior was measured as follows:â‘ The electrorheological(ER) behavior of the Ni/(TiO₂+Urea) particles were closely associated with heat treatment temperature and urea content. The shear strength decreased significantly when heat treatment temperature is above 320℃. When the mass ratio of urea/Ti is 30%, the shear stress reaches 40kPa (the DC electric field is 4kV/mm), which is 10 times as much as that of non-urea ones. However, the shear stress decreased when excessive urea was added. At the same condition the shear strength of Ni/(TiO₂+Triethanolamine) electrorheological fluid is 36kPa and the one of Ni/(TiO₂+SDBS) electrorheological fluid is only 17kPa. The resistance to settlement was improved from 85% to 95% when the electrorheological fluid was modified by SDBS. The microstructure observation of the ER fluids under DC electric field showed that the particles aggregated to form thicker and dense column structure when the mass ratio of urea/Ti is 30%, while the column structure were broken when excessive urea (>30%) was added. A thin and loose column structure was formed in non-urea added ER fluid. It is suggested that the ER behaviors is substantially correlated with the polar molecules in urea.â‘¡The effect of the urea on the electrorheological(ER) behavior, magnetorheological (MR) behavior, and electromagneticrheological (EMR) behavior was investigated. The results indicate that the addition of urea has no effect on the MR activities. However, the addition of urea effectively improve the ER activities of the particle .The shear strength of EMR can reach 55kPa under an electric field of 2kV/mm and magnetic field of 148kA·m^-1. In contrast, the shear strength of the EMR of the Ni/TiO₂ particles (no urea) is only 45kPa. Polar groups in urea are important for the EMR effect; The magnetorheological(MR) property of different Ni/(TiO₂+SDBS) particles which were obtained by Ni with different diameters was investigated. The result shows the shear strength of Ni/(TiO₂+SDBS) and Ni/TiO₂ particles with 150nm reach to 47kPa; The microstructure observation of the Ni/(TiO₂+Urea) particles under the electromagnetic coupling field showed that particles have thick and dense cylindrical structure, so the addition of urea could increase the strength of the EMR under electromagnetic coupling field.