Fabrication Of Practical Magnetorheological Fluids And Their Properties

Magnetorheological fluid (MRF) is a kind of semi-active smart materials, which is a type of suspension that contains magnetic particles and a carrier fluid. MRFs exhibit a controllable magnetorheological (MR) behavior of changing from a fluid state to a solid-like state within milliseconds while subjected to an external magnetic field. Additionally, the strength of the shear stress and the viscosity increases dramatically according to the strength of the external magnetic field. This character is applied in many fields, commercial devices based on MRF have been developed and applied, such as shock absorber, brake valve, clutch, damper, and so on. In this research, the goal was focused on the components of MRF (Soft magnetic particles, Additives, Non-magnetic fluid). Specifically, composite magnetic particles were synthesized, characterized, and been made into MRF to evaluate the MR effects. The contents are as follow:1. Introduction to the properties of magnetic materials, the advances in magnetic nano-materials and MR materials. Overview of the fabrication and surface modification of nano-magnetic materials. Importantly, the constitution, classification, rheology theory and the problems in the process of researching on the MRF materials were discussed.2. On the purpose of tackling the sedimentation of MRF, a kind of Carbonyl Iron-Polymethyl Methacrylate (CI-PMMA) composite magnetic particles were encapsulated via emulsion polymerization. The CI-PMMA composite particles were characterized by SEM, TEM, XRD, FTIR, TGA, XPS, and the MRF were tested on a rheology instrument (Anton Paar, Physica MCR 301). It is found that the CI-PMMA based MRF showed a high shear stress and excellent sedimentation stability, which did not take place in settlement over 6 months.3. Starting from the property of additives, thixotropic agent, nano magnetic particles were taken into consideration, and different kinds of additive based MRF were produced. The MRF adding SiO2 inside displays lower initial viscosity and moderate shear stress. The one adding nano magnetite shows strong shear stress and good sedimentation stability.4. In order to acquire even higher shear stress, a chemical co-precipitation of Co(â…¡) and Fe(â…¢) in alkali aqueous atmosphere on the surface of CI particles was employed to prepare CI- CoFe2O4 composite magnetic particles. And the CI- CoFe2O4 based MRF demonstrates a relatively high shear stress of 90kPa at a magnetic field of 0.7T.