In order to prepare magnetorheological fluid with excellent sedimentation stability, various surfactants are applied to coat carbonyl iron powder. The prepared magnetorheological fluid shows excellent sedimentation stability when the surfactants are respectively sodium lauryl alcohol phosphate, compound sodium fatty acid methyl ester sulfonate, ethylene glycol monostearate and glyceride monostearate. Orthogonal tests are carried out for the optimal combination of surfactants and thixotropic agent. The experimental results show that the optimal combination of additives for MRF is 1.5 wt% of sodium lauryl alcohol phosphate, 1.0 wt% of compound MES, 1.5 wt% of ethylene glycol monostearate, 1.5 wt% of glycerol monostearate and 1.0 wt% of hydrophobic fumed silica. Magnetorheological fluid is prepared by the compound scheme, of which the viscosity is 1.09 Pa·s at 25.9°C and the sedimentation rate is 1.61% after one-week placement. The novel MRF is in excellent sedimentation stability and fluidity.

A magnetorheological fluid (MR fluid) is mainly composed of soft magnetic particles, surfactants, and the base carrier fluid. Among these, soft magnetic particles and the base carrier fluid influence the MR fluid significantly in a high-temperature environment. Therefore, a study was carried out to investigate the changes in the properties of soft magnetic particles and base carrier fluids in high-temperature environments. On this basis, a novel magnetorheological fluid with high-temperature resistance was prepared, and the novel magnetorheological fluid had excellent sedimentation stability, of which the sedimentation rate was only 4.42% after heat treatment at 150 °C followed by one-week placement. At 30 °C, the shear yield stress of the novel fluid was 9.47 kPa under the magnetic field of 817 mT: higher than the general magnetorheological fluid with the same mass fraction. Moreover, its shear yield stress was less affected by the high-temperature environment, reducing by only 4.03% from 10 °C to 70 °C. The novel MR fluid can be applied to a high-temperature environment, effectively expanding the application range of MR fluid.

Magnetorheological fluids, especially those in high-power magnetorheological devices, inevitably work at high temperatures because of the wall slip, energized coils and frictions between particles. The novel magnetorheological fluid for high temperatures can be applied to most magnetorheological devices, especially high-power magnetorheological devices.

Rheological property is very important for magnetorheological fluids, but tribological property also is a crucial factor to determine whether magnetorheological fluids can work stably. In order to find suitable carbonyl iron powder for magnetorheological fluids, three magnetorheological fluids are prepared by ordinary, reduced, and phosphated carbonyl iron powders, and their properties are compared. The microstructures of the different carbonyl iron powders are observed by scanning electron microscopy and X-ray diffraction. Sedimentation stability of the magnetorheological fluids is obtained by observation. The tribological and rheological properties are measured by friction testing machine and rotational rheometer. The results show that MRF-pho have superior tribological property and sedimentation stability, MRF-ord have higher shear yield stress, MRF-red have better comprehensive properties.