Rheological properties and dispersion stability of magnetorheological (MR)suspensions

In the present article, the theological responses and dispersion stability of magnetorheological (MR) fluids were investigated experimentally. Suspens ions of magnetite and carbonyl iron particles were prepared as model MR flu ids. Under an external magnetic field (H-0) and a steady shear flow the yie ld stress depends upon H-0(3/2). The Yield stress depended on the volume fr action of the particle (phi) linearly only at low concentration and increas ed faster at high fraction. Rheological behavior of MR fluids subjected to a small-strain oscillatory shear flow was investigated as a function of the strain amplitude, frequency, and the external magnetic field. In order to improve the stability of MR fluid, ferromagnetic Co-gamma -Fe2O3 and CrO2 p articles were added as the stabilizing and thickening agent in the carbonyl iron suspension. Such needle-like particles seem to play a role in the ste ric repulsion between the relatively large carbonyl iron particles, resulti ng in improved stability against rapid sedimentation of dense iron particle s. Furthermore, the additive-containing MR suspensions exhibited larger yie ld stress, especially at higher magnetic field strength.