Magneto Rheological properties of Cobalt ferrite based MR fluids

Abstract

Magneto Rheological fluids are made of soft magnetic particles dispersed in a carrier fluid. Here cobalt ferrite based magneto rheological fluids were made from the nanopowders of cobalt ferrite obtained from the simple wet chemical synthesis from the metal salts dispersed in the Polyvinyl Pyrrolidone (PVP). The nanoparticle Cobalt ferrite was heat treated at 600C for five and half hours in a furnace. The sample was characterized by using Xray Diffraction(XRD), Scanning Electron Microscopy(SEM) and Energy Dispersive X-ray Analysis (EDAX). Cobalt ferrite which is mixed with different weight percent solutions of PVP to make the Magneto Rheological fluid samples. These samples were characterized by the Rheometere in both oscillatory, rotational measurement conditions. The variation in viscosity with respect to the magnetic field, storage and loss modulus and damping of the samples were measured and presented in this paper. Magneto rheological (MR) fluids are dispersions of fine magnetically soft, multi domain particles. MR fluids exhibit rapid, reversible and significant changes in their viscosity and shear modulus when subjected to external magnetic field. The apparent yield strength of these fluids can be changed significantly within milliseconds by the application of an external magnetic field [13]. MR fluid devices are being used and developed for shock absorbers, clutches, brakes, and seismic dampers[4].The physical properties of an MR fluid change as a nonlinearly time varying function of applied field driven particle alignment with the typical hysteresis of magnetic materials [5]. The external magnetic field applied to the MR fluid causes changes in all physical properties of the fluid, such as Electrical conductivity, thermal conductivity, permeability, as well as viscosity[3, 68].MR fluid viscosity is very much sensitive to changes on external magnetic fields. Viscosity depends on particle concentration, particle shape, size and material in combination with several carrier fluids [5]. In the current MR devices control of the viscosity is performed by the direct excitation of the external magnetic field. The non-linear, hysteretic time varying response of the fluid is an obstacle to precision viscosity control despite fast response time. Most of the times the MR fluids encounter different operating conditions in which their visco elastic properties plays a vital role. Therefore an understanding of the dynamic behavior of the MR fluid will be crucial for the design[9]. Most of the MR devices operate under dynamic conditions (vibrators, dampers, etc) thus small amplitude oscillatory and rotational measuring rheometer provide more useful results [10]. Keeping these points in view, in the present study we have made an MR fluid which is comprising of magnetically soft Co ferrite nano powders weight percent solutions of PVP and studied their oscillational and rotational viscoelastic properties and results are presented in this paper.