Preparation And Performance Of The Iron Nanoparticles And Iron Nanoparticles/Carbonyl Iron Particles Co-doped Magnetorheological Fluids

The sedimentation caused by the great density mismatch between particles and carrier fluids is one of the major barriers that prevent the convention MR fluids from wide applications.The current methods commonly used to improve the sedimentation stability of MR fluids are usually accompanied by a significant reduction in MR effect,which results in the overall performance of MR fluids cannot be taken into account.Therefore,it is a great challenge to make a balance between MR effect and sedimentation stability for MR fluids.Iron nanoparticle would be a good candidate to achieve this balance.In this work,the DC electric arc discharge method was used to prepare iron nanoparticles,which were used as the dispersed phase to prepare iron nanoparticles-based MR fluids.Further,the prepared iron nanoparticles were doped with the commercial micron carbonyl iron particles to prepare the iron nanoparticles/carbonyl iron particles co-doped MR fluids with different doping ratios.Their rheological properties and sedimentation stability were evaluated and compared with the micron carbonyl iron particles-based MR fluids to explore the influence rules and mechanisms.The morphology,magnetic properties,crystal structures and surfaces chemical composition of the prepared iron nanoparticles were examined.The results indicate that they are spherical particles with particle sizes of 30-50 nm,and have high saturation magnetization(~146emu/g)and high purity.The rheological properties test and sedimentation stability test results of iron nanoparticles-based MR fluids show that their shear yield strength are slightly lower than that of the carbonyl iron particles-based MR fluids,but the sedimentation stability present a significant advantage.The rheological properties and sedimentation stability of the iron nanoparticles/carbonyl iron particles co-doped MR fluids with different doping ratios were evaluated,and the influence rules and mechanisms of doping ratios of micro-nano particles on the performance of MR fluids were explored.The results show that the sedimentation stability of the iron nanoparticles/carbonyl iron particles co-doped MR fluids improved significantly with the increase of the proportion of iron nanoparticles,which is attributed to the help of both free state and adsorbed state iron nanoparticles in MR fluids.And the effect of the addition of iron nanoparticles on rheological properties under magnetic field is a combination of two opposing factors: the strengthening of the structure and the weakening of magnetization.Furthermore,within a specific magnetic field strength range,the co-doped MR fluids fluids with some certain doping ratios can achieve an improvement in both rheological property and sedimentation stability compared with carbonyl iron particles-based MR fluids.