Abstract
Magnetite powders were prepared by coprecipitation method, and followed by coating of monomolecular oleate ion. The kerosene base magnetic fluids were obtained by dispersing the powders in kerosene. In this paper, the effects of temperature on the chemical stability of surface-coated magnetite, the magnetic properties of magnetic fluid and its viscosity were examined.
The results obtained are as follows: (1) The surface-coated magnetite is oxidized to a-hematite in the air at about 200°C because of combustion of oleate. (2) The change in the magnetization of magnetic fluid with temperature corresponds to that of magnetite powders. This means that the surface-coated magnetite is fairly stable in kerosene against the change in temperature. (3) Considering that the surface-coated magnetite contains a slight amount of non-magnetic part, the magnetization curve can be explained by Langevin's theory. (4) The magnetic fluids, whose magnetite fractions are less than 0.65 g/ml, show Newtonian flow. For the dependence of temperature on the viscosity of those fluids, Andrade's equation is applicable to the region of 20°C-80°C.
