Xperimental Studies on the Rheological Properties of Cobalt Ferrite Nanofluids

Cobalt ferrite (CoFe2O4 ) nanoparticles and corresponding cobalt ferrite nanofluids are one of the most recently explored magnetic particles by their improved magnetic properties in comparison with the conventional ferrofluids. In this paper, the viscosity behaviors of two types of cobalt ferrite nanofluids were studied. One of these was based on CoFe2O4 ferrimagnetic particles with an average diameter of 10.7 nm, whereas the other was based on CoFe2O4 superparamagnetic particles of 5.8 nm in diameter. The dynamic viscosities of these nanofluids were measured as the shear rate dependence under the magnetic field of various intensities, using a rotating rheometer. The cobalt ferrite fluids exhibit a yield shear-thinning behavior with and without magnetic field application. The magnetoviscous effects are somewhat lower than those of the standard iron oxide ferrofluids. The more substantial magnetorheological effect in the case of nanofluids based on super para magnetic particles is observed. This result is attributed to the difference in number density and magnetic properties of both fluids. The concentration-dependent viscosity of the cobalt ferritefluids was considered. The experimental data indicate that the viscosity is enhanced with the increase of magnetic field strength and nanoparticle weight fraction. At the shear rate high enough, the viscosity of all the fluids tends to saturate at the concentrations higher than 5%.