The enhanced coating effect of carbonyl iron particles and improved dispersion stability of magnetorheological fluid

Abstract The coating effect of 1,2-bis(triethoxy-silyl)ethane (BTES) on the carbonyl iron particles (CIP) was enhanced through the etching of CIP by adjusting the concentration of hydrochloric acid (HCl), leading to a significant improvement in the dispersion stability of the magnetorheological fluid (MRF). The microstructures, coating effect and magnetism of the CIPs were examined using the scanning electron microscopy (SEM), automatic surface and porosity analyzer (BTE), fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and vibrating sample magnetometer (VSM). Furthermore, the rheological properties and dispersion stability of the MRFs were assessed using a rotating rheometer and turbiscan-tower. The results shown that with the concentration of HCl increased, the nanopores appeared on the CIPs and then disappeared, and the specific surface area of the particles increased and then decreased. The number of nanopores sharply increased and the specific surface area of particles sharply increased to 37.7697 m2/g when the concentration of HCl reached to 0.50 mol/L. As the concentration of HCl increased, the coated mass of BTES on the particles increased. The coated mass loss was less than 1 wt.% when the concentration of HCl was below 0.50 mol/L, and the coated mass loss increased to 2.45 wt.% when the concentration of HCl was 0.5 mol/L, the coated mass was effectively enhanced by the HCl of higher concentration. As the concentration of HCl increased, the saturation magnetization of particles decreased, and a sharply decrease appeared when the concentration of HCl was 0.50 mol/L, the saturation magnetization of coated particles further decreased from 196.7 emu/g to 113.3 emu/g. As the coated mass of particles increased, the viscosity and shear stress of MRFs increased and the increase was significant when the coated mass loss of particles above 2.45 wt.% without a magnetic field, while which decreased under a magnetic filed. As the coated mass of particles increased, the sedimentation rate of particles decreased from 0.13 to 0.01 mm/h, when the coated mass loss of particles was more than 2.45 wt.%, the sedimentation rate of all MRFs were close to 0.01 mm/h. The coating effect was greatly enhanced by controlling the concentration of HCl, and thus the MRF with superior shear stress and excellent dispersion stability was obtained.