Rheological properties and suspension stability of magnetorheological fluid based on Fe₃O₄ hollow spheres

Magnetorheological fluid (MRF) is a material whose viscosity can be changed by a magnetic field. However, one of the challenges with MRF is that the magnetic particles (MPs) used often settle out of suspension, reducing its effectiveness. To improve the suspension stability and rheological properties of MRF to some extent, this paper prepares Fe3O4 hollow spheres using a simple, one-step synthetic solvothermal method. The surface morphology, particle size distribution, and crystal structure of Fe3O4 hollow spheres are characterized. The results show that the shell thickness of Fe3O4 hollow spheres forms about 100 nm and a saturation magnetization intensity of 86.33 emu/g at a ratio of FeCl3 & sdot;6H2O to CO(NH2)2 substance of 1:10 when the porosity agent urea is 0.06 mol. Furthermore, MRF is prepared using dimethyl silicone oil as the base carrier fluid. Suspension stability and rheological properties of MRF are investigated by varying the content ratio of Fe3O4 hollow spheres. While increasing the mass fraction of Fe3O4 hollow spheres, the viscosity and shear yield stress of MRF increase. MRF based on Fe3O4 hollow spheres significantly improves the suspension stability and rheological properties of the fluid, making it more suitable for practical applications.