Evaluation of magnetorheological suspensions based on carbonyl iron powders

The particle size distribution and magnetic susceptibility of some commercial carbonyl iron powders (code names CC, CS, HQ OX and SM) were measured. The particle size of the powders increases as follows: HQ<SM<CC approximate to OX<CS. The magnetic susceptibility increases in the order: HQ ≈ OX<<SM; CC ≈ CS. Magnetorheological suspensions (MRS) with 66% w/w of iron were prepared and their rheological properties were evaluated at no field, 100, 200 and 300 Oe. The yield stress under 300 Oe measured with strain-stress curves increases in the order: HQ ≈ OX<SM<CC<CS, showing direct correlation with the susceptibility. The plastic viscosity without field increases in the order: CS<CC<OX<SM<HQ, an inverse correlation with particle size. These results show that the particle size and/or size distribution can be another important property of the powders, together with magnetic susceptibility on the formulation of improved MRS.