Creep measurements on magnetic suspension

Rheological properties of disperse system of magnetic ϒ-Fe2O3in silicone oil were investigated by the aid of creep experiments. The flow curve shows a typical pseudo-plastic flow pattern of which plastic viscosity is about 82.6 poise and apparent yield stress is about 1800 dyne/cm2. These phenomena are attributable to structural networks formed by dispersed magnetic particles. The suspension with denser network structure was thought to behave as an elastic solid at the stress under the true yield stress. However, an irreversible flow behavior has been observed in creep measurements at the stress which is smaller than the true yield stress. In the disperse system, the structural networks of dispersed particles depend on a flow history and their mechanical behavior seems to be a function of time. In the creep experiment at various magnitudes of shear stress measured immediately after cessation of shear flow, the density of structural networks seems to increase depending on the applied force at initial time region, however with increasing time, the irreversible flow becomes dominant in their creep behavior. An elastic behavior of interparticle network structure can be presumed by a creep recovery. The elastic modulus estimated from the relationship between the applying stress and the recoverable strain is about 1100 dyne/cm2.