| As a member of smart materials, Magnetorheological fluid (MRF) usually consists of micron-sized soft magnetic particles, carrier liquid and additive. They show a unique ability to undergo rapid, nearly completely reversible, significant changes in their rheology once an external magnetic field is applied. MRF can be applied in shock damper, clutch, tumor therapy, magnetorheological polishing, and so on. Now study on MRF has already been a hot subject in material science field. Currently the magnetic particles in MRF are mainly carbonyl iron dust. However, the cost of carbonyl iron dust is higher, which restricts MRF's application in industry. Now it is urgent to find a new way of reusing the iron scale which is the solid waste during the preparation of iron and steel, although there have been some methods of recycling. In this paper Iron scale as starting material was solved by H2SO4, and FeSO4 solution was got after purification. Then a-Fe2O3 powder was prepared by precipitation method using FeSO4 After a-Fe2O3 was reduced by H2, the reduced ferrous powder was mixed with silicone oil to prepare iron magnetorheogical fluid (MRF) and the properties of MRF were studied.During the preparation of nm a-Fe2O3 powder, the selection of precipitants and the temperatures of reaction and incineration were discussed. And the samples were characterized by TG-DTA analysis, X-ray diffraction, FI-IR, TEM and Mossbauer spectrum.(NH4)2CO3 as the precipitant was the best selection. The mass fraction of a-Fe2O3,which was prepared after reaction at 50℃and incineration at 500℃for 2h, is 98.77%.The patterns of a-Fe2O3 particles, the size of which was between 30nm and 50nm, have spheric shape and spheroidicity. The average hyperfine magnetic field increased as the temperature of incineration increased due to surface effect and magnetic induced effect of microaggregates.The size of a-Fe2O3 particle had effects on the time of reducing and the patterns of reduced ferrous powder. The patterns of reduced ferrous powder changed from bacillary to spheric shape and the required time of reducing became longer as the size of a-Fe2O3 particles increased. The mass fraction of Fe element in iron dust reduced at 650℃for 3h from a-Fe2O3 calcined at 500℃was 99.2%.In iron dust the mass fraction of malleable cast-iron was 93.1% and the mass fraction of Fe-N solid solution was 6.9% by mossbauer spectrum analysis. The color of reduced ferrous powder was hoar and the density of reduced ferrous powder was 0.66 g/cm3.The saturation magnetization of reduced ferrous powder was the same as that of carbonyl iron dust and the response property of reduced ferrous powder is better than carbonyl iron dust under magnetic field between 0 and 250kA/m.According to the requirements of carrier and solubility in carrier, silicone oil and NQ-71 were selected as carrier and surfactant respectively. The results showed that after reduced ferrous powder was coated, it dispersed better in silicone oil.The properties of MRF were tested by MCR301 rheometer. The iron MRF not only had good stability, but also could reach its maximum shear stress quickly under low magnetic field. And these features can be helpful to apply prepared iron MRF in actual projects.This phenomenon that under no magnetic field the viscosity of MRF decreased as the rate of shear increased was the same as others reported and after the curves were fitted, prepared iron MRF belonged to Bingham fluid model. When applied medium magnetic field the viscosity of MRF decreased as the rate of shear increased. This showed prepared iron MRF also belonged to Bingham fluid model under medium magnetic field. The shear stress and viscosity increased when the nm Fe3O4 particles were added in iron MRF and the experiments showed that when the mass fraction of nm particles was 0.8% the increase was the biggest and when the mass fraction of nm particles continued to increase the shear stress began to decrease.
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