Magneto-mechanical response of additive-free Fe-based magnetorheological fluids: role of particle shape and magnetic properties

The flow properties of carbonyl iron (CI) and electrolytic iron (EI) micro-particles based magnetorheological fluids (MRFs) were studied under steady shear conditions at different applied magnetic field strengths (B). The CI particles were spherically-shaped having a wide size distribution ranging from similar to 0.2 to similar to 3 mu m whereas the EI particles were irregularly-shaped with much bigger particles of sizes between similar to 20 mu m and 80 mu m. To prepare the MRFs, 40 wt% each of CI and EI micro-particles were separately dispersed in silicone oil. In the MRFs the particles do not contain any surfactant/coating and the MRFs do not include any stabilizers in them. According to the magnetorheological results, although the yield strength (tau(Y)) and viscosity (eta) of both MRFs increase with increase in B, there is deviation from the parallelism in increase of tau(Y) and eta with B. This suggests that tau(Y) and eta depend strongly on the physical parameters of Fe-particles such as the shape, size and saturation magnetization. The effect of saturation magnetization on steady state shear response of the MRFs dominates over the effect of shape and size of the particles.