| 摘要 |
PROBLEM TO BE SOLVED: To provide a method of manufacturing a magnetic fluid which is superior in stability at a high temperature, when magnetic fine particles are dispersed in a low vapor-pressure base oil by the use of oil-soluble sulfonic acid surface-active agent. SOLUTION: Magnetic fine particles such as ferrite fine particles are coated with unsaturated higher fatty acid whose surface coverage is about 20 to 70% or saturated higher fatty acid, whose surface coverage is about 25 to 55%. Oil-soluble surface-active agent is added to a dispersed system, composed of an organic solvent as a dispersion medium and the magnetic fine particles as the dispersed phase, and the surface-active agent is made to adsorb matter by the use of ultrasonic waves. After the adsorbed matter is recovered, the magnetic fine particles are dispersed into low vapor pressure base oil for the manufacture of a magnetic fluid. |
