Effect of milling time on rheological properties of plate- like carbonyl iron particles in magnetorheological fluid

Abstract

Magnetorheological (MR) fluid is a magnetic field responsive fluid containing polarizable particles and a liquid carrier component. This MR fluid is typically used within the working gap of dampers to provide varied damping forces, depending on magnetic field strength. Generally, maximum yield stress will be increased with the increasing amount of particles in the MR fluid, and consequently enhancing the maximum force output of the device. An additional number of particles also lead to increasing the off-state viscosity and sedimentation of the MR fluid. Researchers have concentrated on improving the properties of particles to overcome the sedimentation problem. Particle shape is a critical factor to enhance the sedimentation stability. Thus, this research aims to synthesize the plate-like carbonyl iron (Cl) to enhance the maximum yield stress and stability of the suspension fluids. Several sizes of plate-like Cl were produced using the ball milling method, with the variation of milling time. Observation from X-ray Powder Diffraction, Scanning Electron Microscope and Vibrating Sample Magnetometer results showed that milling duration play a crucial role in controlling the plate-like Cl's microstructure, morphology, and consequent magnetic properties obtained from the ball-milling route. The crystallography phase of Cl particles was conserved after the milling process, and it is flattened, resulting in the enhancement of the particle length and surface area. Accordingly, the plate-like Cl obtained a larger contact surface, which builds stronger clusters due to the magnetic field and resulted in higher saturation magnetization than the spherical CL This study identified that the sedimentation stability of the plate-like Cl-based MR fluid increased significantly due to the increase of the friction force resulted from the increase of the surface area of particles. Subsequently, the field-dependent rheological test demonstrated that the yield shear stress of the plate-like Cl-based MR fluid increased up to 134% compared to the spherical Cl-based MR fluid. In sum, this study found that Cl particles which undergo 20 hours of milling has the best parameter to be used in MR fluid.