Information AboutMagnetorheological Fluid |
| CATEGORIES ABOUT FERROFLUID | |
| magnetism | |
| continuum mechanics | |
| plasma physics | |
|
A ferrofluid is a specific type of liquid which responds to a Fluid . The Solid particles are generally stabilized with an attached Surfactant layer. DESCRIPTION True ferrofluids are stable. This means that the solid particles do not agglomerate or phase separate even in extremely strong magnetic fields. The term magnetorheological fluid (MRF) refers to liquids similar to ferrofluids (FF) that solidify in the presence of a magnetic field. Magnetorheological fluids have Micrometre scale magnetic particles that are 1–3 orders of magnitude larger than those of ferrofluids. DIFFERENCE BETWEEN MRFS AND FFS A FF on the contrary does not form chains. The random movement of the particles is larger than the force pulling them together. Their viscosity doesn't change, but they like to stay in high magnetic fields. The magnetorheological effect starts above a particle size of 10 Nanometer s. Ferrofluids are Superparamagnetic and have very low Hysteresis . The particles are usually iron, magnetite, or cobalt, and are smaller than a magnetic domain, typically 10 Nanometer s in diameter. The surrounding liquid is typically oil or water (or possibly wax). Surfactant s are used to make the suspension more stable, so that the Micelle -trapped particles repel each other due to Steric hindrance effects. Ferrofluids form intriguing three-dimensional shapes in the presence of magnetic fields, and patterns of stripes when confined to a thin sheet (as between two plates of glass) due to the individual particles' magnetic fields aligning and repelling each other and the opposing surface tension forces of the liquid holding them together. APPLICATIONS They are used in Loudspeaker s to sink heat between the voice coil and the magnet assembly, and to passively damp the movement of the cone. They reside in what would normally be the air gap around the voice coil, held in place by the speaker's magnet. Ferrofluids are similarly used to form liquid seals around the spinning drive shafts in Hard Disk s. Using electromagnets and sensors, the Viscosity of magnetorheological fluids can be controlled dynamically, allowing for active damping (in car Shock Absorber s like Delphi Corporation 's MagnaRide , for instance). This allows hundreds of watts of mechanical power to be controlled with a few watts of electrical power, which is much more efficient than other methods of vibration control, such as Piezoelectric crystals. They also have friction-reducing capabilities as well. If applied to the surface of a strong enough magnet, such as one made of Neodymium , it can glide across smooth surfaces with minimal resistance. Industries Matsushita Electric Industry produced a printer capable of printing 5 pages per minute using a Ferrofluid ink. Defense The United States Air Force introduced a Radar Absorbent Material (RAM) paint made from both ferrofluidic and non-magnetic substances. By reducing the Reflection of Electromagnetic Waves , this material helped make Aeroplanes invisible to RADAR . Measurement Ferrofluids have numerous Optical applications due to their Refractive properties; that is, each grain, a Micromagnet , reflects light. These applications include measuring Specific Viscosity of a liquid placed between a Polarizer and an Analyzer , illuminated by a Helium - Neon Laser . Medicine In Medicine , a Compatible ferrofluid can be used for Cancer detection. HOME-MADE MAGNETORHEOLOGICAL FLUID A simple magnetorheological fluid can be home-made out of small magnetic particles mixed with mineral or vegetable oil. Iron filings do not work well; they are too big. Good sources for small magnetic particles are:
These fluids are not very stable, however. The particles will tend to clump and the fluid properties will be lost quickly. Fluids created for professional purposes use Emulsifier s to suspend very small oily (octane or kerosene) magnetic particles in water. The particles are very fine; less than a micrometre in diameter. SEE ALSO REFERENCES: Ferrohydrodynamics (1985), Ron Rosensweig's. The usual starting reference for learning the details of ferrofluids. EXTERNAL LINKS
|
|
|