| 摘要 |
PURPOSE:To obtain such a magnetic fluid that the magnetization of the fluid abruptly changes against magnetic fields and, therefore, the fluid shows a large apparent density in a relatively low magnetic field by mixing two or more kinds of fine magnetic particles which are magnet ized differently from each other. CONSTITUTION:This magnetic fluid, in which magnetic fine particles are dispersed in a dispersing medium after chemically treating the surface of the articles with a surface active agent, is composed of two or more kinds of fine magnetic particles which are magnetized differently from each other. For example, sodium oleate which is adjusted to 12 in pH with caustic soda is added to the mixture of fine magnetic particles prepared by equally mixing two kinds of fine magnetic particles (a) and (b) magnetized differently from another by an amount at which the content of the magnetic fine particles can become 30 dry wt.% and the fluid thus prepared is aged for 60 minutes at 90 deg.C. Then the fluid is cooled to <=60 deg.C and adjusted in pH to 5.3 with hydrochloric acid, and then, dehydrated by filtration after cleaning the fluid with water by repeating decantation 10 times. After dehydration, dodecyl benzensulfonic acid soda is added by an amount at which the content of the magnetic fine particles can become 20 dry wt.% and the fluid is stirred and mixed for 50 minutes. As a result, a magnetic fluid whose apparent density largely changes nonlinearly is obtained. |
