Research On Sedimentation Stability And Rheological Properties Of Reduced Iron MRF

Magnetorheological fluid (MRF) is a new type of functional materials, which has fluid characteristics and the characteristics of intelligent control and it is one kind of suspension composed of magnetic particles, carrier liquid and additives. Under external magnetic field, MRF can be instantly transformed into Bingham fluid from Newtonian fluid and has a larger shear stress, which can be applied to damper, clutch, magnetorheological polishing, and so on. Currently the issue is MRF has less stable settlement, that seriously impact on the application of MRF. In this paper, reduced iron powder and carbonyl iron powder are selected as magnetic particles for the preparation of MRF, and the properties of MRF are studied from particles volume fraction, surfactants, additives and so on for the purpose of improving sedimentation stability and rheological properties.In this paper steel waste iron scale as raw material was solved by H2SO4, and after purification FeSO4solution was got. Then Fe2O3powder was prepared by precipitation method using FeSO4. After Fe2O3was reduced by hydrogen at650℃for four hour, the reduced iron powder could be got. Iron is up to93.2%by XRD and Mossbauer spectrum analysis. Besides, by detecting reduced iron powder and carbonyl iron powder through SEM and VSM, the size of reduced iron powder is mainly in the15～20μm, He reaches to8.05Oe and Ms223.56emu/g and the size of carbonyl iron powder is mainly in the1～5μm, He reaches to8.05Oe and Ms223.56emu/g. The greater the saturation magnetization of magnetic particles, the shorter response time and the greater shear stress of magnetorheological fluid. The smaller the coercive force, the smaller the hysteresis loss. Therefore, compared with MRF prepared with reduced iron powder, response time of MRF prepared with carbonyl iron powder is shorter and shear stress is larger. But since He of reduced iron powder is smaller than that of carbonyl iron powder, so the hysteresis loss of MRF prepared with reduced iron powder is lower and more conducive to practical application. With high saturation magnetization and low coercive force, both can be used to prepare magnetorheological fluid.Silane coupling agent KH-550and oleic acid are used as surfactant, dissolved in isopropyl alcohol mixed with magnetic particles stirring at60℃for half an hour and then dry one hour in a vacuum oven at80℃after by mechanical milling. Coated magnetic particles corresponding to Fe five diffraction peaks have emerged broadening and strength are significantly lower. Also the Ms of reduced iron powder reaches to186.91emu/g, carbonyl iron powder198.94emu/g. Add nano-SiO2and organic bentonite into coated magnetic particles, mixed with silicone oil milling4h and we can obtain magnetorheological fluid.Viscosity and shear stress of magnetorheological fluid are tested by MCR301rheometer and the results show that magnetorheological fluid has taken placed an apparent shear-thinning phenomenon under zero field and magnetic field which is a typical non-Newtonian fluid. Experimental results prove that the35%volume fraction of MRF has not only low viscosity and high shear stress under magnetic field but also good sedimentation stability. Using surfactants of KH-550mixed with oleic acid and the addition of nano-SiO2could enhance shear stress and sedimentation stability of MRF to some extent. The amount of surfactant reaches to5%, additives2%when the result is best. The sedimentation stability of MRF prepared with carbonyl iron powder is better than prepared with reduced iron powder and its viscosity is low and shear stress reaches to34.9kPa, larger than MRF prepared with reduced iron powder.