Preparation,Characterization And Magnetorheological Behavior Of Fe₃O₄ Particles With Different Morphologies

Magnetorheological fluid?MR?belongs to a kind of smart materials with controllable rheological properties.It has excellent properties such as fast response?millisecond order?,continuous adjustment and low energy consumption,and it has shown a great application potential in engineering fields.Traditional MR fluids have problems such as poor sedimentation stability and insufficient mechanical properties,which seriously limit the development of MR fluids.Magnetic particles are an important part of MR fluids and their morphology,size,microstructure and magnetic properties directly affect the comprehensive performances of MR fluids.The most widely used magnetic particles are commercial carbonyl iron?CI?particles.Although the CI particles have high magnetic properties,the sedimentation stability of the corresponding MR fluid is poor due to their high powder density.This limits the MR performances and practical applications of the MR fluid.Therefore,the design and development of new magnetic particles with different morphologies and structures have become a hot spot in the research of MR fluids.In this study,two kinds of Fe₃O₄ magnetic particles with different morphologies were prepared by a facile solvothermal method.The morphology,structure and physicochemical properties of the particles were fully investigated by scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,X-ray diffractometry?XRD?,and X-ray photoelectron spectroscopy?XPS?,thermogravimetric analyzer?TGA?,automatic specific surface area analyzer and vibrating sample magnetometer?VSM?.Two kinds of MR fluids were prepared by using magnetic particles as the dispersed phase and silicone oil as the continuous phase.The rheological properties of MR fluids were tested by a rotational rheometer and their sedimentation stability was examined by a static observation method.The main results are listed as follows.?1?A two-step solvothermal-calcination method was used to prepare hierarchically structured flower-like Fe₃O₄ particles with an average diameter of 3.2?m.The results of SEM and TEM indicated that many pleats were observed on the surface of the particles.The special structure of the petal shape is favorable for increasing the contact area with the base liquid,generating a larger drop resistance and achieving the effect of slowing the sedimentation rate.The yield strength reached 867 Pa when the magnetic field strength was 250 kA/m.The sedimentation ratio of flower-like Fe₃O₄ particles-based MR fluid was 86.5%after 15 days settlement,while the settlement ratio of conventional CI-based MR fluid was 62.8%in the same period.The results indicated that the sedimentation stability of flower-like Fe₃O₄ particles-based MR fluid was better than that of the CI-based MR fluid.?2?A one-step solvothermal method was used to prepare porous Fe₃O₄ nanocrystal clusters.The results of SEM and TEM showed that the Fe₃O₄ particles with an average diameter of 250 nm were composed of many tiny nanocrystals,and there were many pores formed due to the agglomeration of nanocrystals.In the MR measurements,its yield strength reached 340 Pa when the applied magnetic field strength was 250 kA/m.The sedimentation ratio was 79.6%after static settlement for 15 days.The sedimentation stability of Fe₃O₄ nanocrystal clusters-based MR fluid was better than that of CI-based MR fluid.The enhanced sedimentation stability can be attributed to the porous structure and the reduced density difference between the dispersed particles and carrier liquid.