Carbonyl iron suspension with core-shell structured Fe3O4@SiO2 nanoparticle additives and its magnetorheological property

Magnetorheological (MR) fluids are known to be colloidal suspensions of magnetic particles dispersed in nonmagnetic fluid, are capable of being solid-like under applied magnetic field and liquid-like by removing the magnetic field [1-3]. Their rheological properties such as yield stress and shear viscosity can reversibly and instantly be changed as a result of dispersed magnetic particles building up chain-like structure under a magnetic field due to magnetic dipole-dipole interaction between particles, and this phenomenon has great potential in designing diverse high performance engineering products including active damper system, torque transducer and MR polishing equipment [4-6]. Generally, high yield stress and low apparent viscosity without magnetic field as well as good stability and durability have become very crucial factors for the MR fluid application. Among various magnetic materials, carbonyl iron (CI) particles have been adopted as a superior candidate for MR fluids due to their high saturation magnetization as well as their appropriate particle size. However, the large density mismatch between CI particles and medium oil leads to serious sedimentation drawback. Therefore, many strategies have been explored to solve this problem [7, 8].