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The dispersion stability of magnetorheological fluid directly affects its application effects, such as absorber and damper, which becomes the focus of current research. In this study, various silane coupling agents were used to coat carbonyl iron powder particles with different thicknesses. The coated particles were dispersed in high viscosity polyalphaolefin synthetic oil (PAO) to prepare a series of magnetorheological fluids. The morphology of particles was observed by SEM, the chemical interaction between silane coupling agent and particles was studied by FTIR, the quality of coating layer on the surface of particles was measured by TGA, and the magnetic properties of particles were analyzed by VSM, in addition, rheological properties and settling stability of the magnetorheological fluid were tested. The results show that with the increase of silane coupling agent coating layer, the coating quality of particles increases, and the saturated magnetization of particles decreases,  and particles are coated by the silane coupling agent through chemical interaction. With the increase of coating thickness, the particle saturation magnetization decreases gradually, and the sedimentation rate of magnetorheological fluid decreases correspondingly, when the coating quality is 7.35%, the sedimentation rate of magnetorheological fluid is only 4% after 100 days standing. The coating layer reduces the coated particle density, whihc prevents the agglomeration of particles and improves the compatibility between particles and PAO. It shows that the magnetorheological fluid has a higher yield stress, and no agglomeration or hardening among the particles appear.
 

Magnetorheological fluid, Silane coupling agent, Coating thickness, Dispersion stability, Settling rate