Effect of Hard Magnetic CoFe<sub>2</sub>O<sub>4</sub> Nanoparticles Additives on Improving Rheological Properties and Dispersion Stability of Magnetorheological Fluids

Increasing dispersion stability is the main issue in recent research at magnetorheological (MR) fluids. The presentation of nanoparticle addictive in MR fluids is an effective method not only to increase dispersion stability but also increasing performance in MR fluids. In this study, the effect of hard magnetic CoFe 2 O 4 nanoparticles addition on rheological properties and dispersion stabilization had been studied. Rheological properties were investigated using a rheometer at room temperature. The result showed that the addition of CoFe 2 O 4 nanoparticles 1wt% in particles of MR fluids were improving the shear stress and viscosity of MR fluids. Both MR fluids with and without nanoadditives behaving like a Newtonian fluid at the off-state condition and act like Bingham fluid at the on-state condition. Moreover, MR fluid with CoFe 2 O 4 additives had a higher sedimentation ratio than MR fluids without additives.