Enhanced Magnetorheological Response of Carbonyl Iron Suspension With Added ZnFe₂O₄ Particles

To improve the rheological performance and dispersion state of carbonyl iron (CI)-based magnetorheological (MR) fluids, we synthesized ZnFe
₂
O
₄
particles via a solvothermal method and used them as an additive material. Morphology of the product particles was examined using scanning electron microscopy, and their particle size distribution was measured via dynamic light scattering. Two types of MR suspensions, CI- and CI-/ZnFe
₂
O
₄
-based MR suspensions, were fabricated by dispersing the particles in silicone oil. Under external magnetic fields of different strengths, the rheological properties of the CI- and CI-/ZnFe
₂
O
₄
-based MR fluids were determined using a rotational rheometer via steady shear and oscillatory dynamic tests. Shear stress curves according to the shear rate were examined using the Hershel–Bulkley model, and the dynamic yield stress curve had a slope of 1.5. Moreover, the ZnFe
₂
O
₄
-containing MR fluid exhibited a larger yield stress than the CI-based MR fluid. The dispersion stability of both MR suspensions was also confirmed using a Turbiscan optical analyzer. The light transmission ratio of the CI-based suspension was 79%, whereas that of the CI/ZnFe
₂
O
₄
suspension was 34%. As an additive material, ZnFe
₂
O
₄
filled the free space among the CI particles and improved the stability of the fluid against rapid sedimentation of dense CI particles.