Some applications of ferrofluid magnetic colloids

Abstract

Ferrofluids are colloidal dispersions of subdomain magnetic partiles ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\bar{D}&lt; 150</tex> Å) that retain their liquid characteristics in the presence of a magnetic field. As a result, ferrofluids are unique liquid media in which it is possible to induce substantial magnetic forces which result in unusual fluid mechanical properties in the presence of an applied field. Magnetic properties may be conferred to a wide range of liquid such as hydrocarbons, water, glycerol, silicones, and even fluorocarbons. The magnetic properties of the ferrofluids can be controlled by varying the composition, size, and concentration of the magnetic particles. The existence of these magnetic fluids has resulted in a number of unique applications. Applications which have been reduced to practice include novel pumps and other energy conversion devices, viscous dampers for gravity gradient satellites, accelerometers, and gyroscope supports employing levitation bearings, specific gravity meters, seals, etc.