Effect of the surface coating of carbonyl iron particles on the dispersion stability of magnetorheological fluid

Abstract

Abstract The dispersion stability of a carbonyl iron particle (CIP)-based magnetorheological fluid (MRF) is improved by CIP, which particle is etched with hydrochloric acid (HCl) to form a porous structure with many hydroxyl groups and subsequently coated with silane coupling agents that have varying chain lengths. The morphological characteristics and coated thickness of the particles are investigated through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) are employed to analyze the coating effect of the silane coupling agents on the particles. The influence of the coating on particle density and saturation magnetization is evaluated using a densitometer and vibrating sample magnetometer (VSM). The rheological properties and dispersion stability of the MRF are assessed utilizing a rotating rheometer and Turbiscan-Lab. The results revealed that after CIPs were etched with HCl, numerous nanopores on their surface. Additionally, as the chain length of the silane coupling agent increases, the coated mass increases, and the coating effect was confirmed chemically, and meanwhile, the density and the saturation magnetization of particles decreased, and the coated particles with different shell thicknesses were obtained. With the chain length increase of silane coupling agent, without a magnetic field, the viscosity of MRF prepared by coated particles increase slightly, due to the enhancement of special three-dimensional network structure; under a magnetic field, the viscosity of the MRF decreased distinctly, due to that the coating of non-magnetospheric increased the distance and decreased the interaction force between the particles. With the chain length increase of silane coupling agent, the sedimentation rate of MRF decreased from 58–3.5% after 100 days of sedimentation, and the migration distances of the MRFs were 22.4 mm, 3.7 mm, 2.4 mm, and 0 mm, with particle sedimentation rates of 0.149, 0.019, 0.017, and 0 mm/h, respectively. The MRF with high dispersion stability was obtained, and the etching of CIP by HCl and the proper chain length of the coating of silane coupling agent were proved effective manners to improve the dispersion stability of MRF.