Investigation of Static Shear Stress in a Suspension of Co0.2Ni0.8Fe2O4 Nanoparticles in Sesame Oil

Abstract

Spinel ferrite nanoparticles of Co0.2Ni0.8Fe2O4 composition are utilized as filler magnetic particles in the carrier fluid of sesame oil to prepare a magnetorheological fluid. The hydrothermal method is adopted to prepare CoNi ferrite nanoparticles. X-ray diffraction analysis is used to check the crystalline phase, and transmission electron microscopy is used to image the particles to find the size and shape of particles. The average size is about 18 nm. The magnetic properties are determined by measuring the hysteresis loop by the superconducting quantum interference device technique. The saturation magnetization is 59.4 emu/g, and the coercivity is 30 Oe. The Langevin fitting is applied to the hysteresis loop to show that the particle moment is about 16 × 103 μB. The viscosity and shear stress are measured against the shear rate, where the latter parameters are extracted from the viscosity and the viscometer spindle speed. The viscosity behavior showed the shear thinning against the shear rate. The viscosity increases with the magnetic field. The shear stress increases with the shear rate and has a very good matching with the Bingham model, rather than with the Herschel–Bulkley model, while describing the measured data. We observed a clear high static shear stress at low shear rates that are growing with the magnetic field. The yield stress was increased linearly with magnetic field strength.