Controllable fabrication of silica encapsulated soft magnetic microspheres with enhanced oxidation-resistance and their rheology under magnetic field

Silica encapsulated core–shell structured carbonyl iron (CI) magnetic particles (CI@SiO2) were successfully prepared via a facile sol–gel method based on the silane grafted CI particles in two steps, and then confirmed by scanning electron microscopy and X-ray energy dispersive spectra. Anti-corrosion property of the as-fabricated CI@SiO2 particles was examined under conditions of being both heated in the air environment and sustained in an acid solution. Magnetorheological (MR) performance of the CI@SiO2 based MR fluid dispersed in silicone oil, including complex viscosity, storage and loss modulus as well as the related loss factor and relaxation modulus, was investigated and compared with that of the CI based MR fluid by using a rotational rheometer equipped with a magnetic device, showing enhanced property of heat-induced oxidation resistance with decreased particle density.