Ferrofluid
Ferrofluid is a novel application of nano technology that was originally developed to control liquid fuel flow in space, and is now used in many commercial applications including computer hard drives, audio speakers, bio-medical procedures and detection of micro-faults in critical steel components (1).
Ferro Fluid is a colloidal suspension of nano scale magnetic particles in a liquid carrier (1). The cores of these particles are made of iron oxides which are known to be compatible with living tissues (2). The particles average about 10nm in size and are coated with a dispersing agent (surfactant) to prevent agglomeration. Normally, the particles are randomly distributed, but in the presence of a magnetic field, each particle aligns along the magnetic force lines so that the fluid behaves as a homogeneous magnetic liquid that responds instantly to changes in the strength and orientation of the magnetic field. (1)
surfactant
A typical ferrofluid may contain by volume 5% magnetic solid, 10% surfactant and 85% carrier. The surfactant must be matched to the carrier type and must overcome the attractive van der Waals and magnetic forces between the particles. (3)
Magnetic Behavior of Ferrofluid
In the absence of a magnetic field, the magnetic moments of the particles are randomly distributed and the fluid has no net magnetization.
When a magnetic field is applied to a ferrofluid, the magnetic moments of the particles orient along the field lines almost instantly. The magnetization of the ferrofluid responds immediately to the changes in the applied magnetic field and when the applied field is removed, the moments randomize quickly. (3)
Ferrofluid & Applications
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 helps to reduce the Radar Cross Section of aircraft (4).
Medicine
Heat Transfer
Ferrofluids are paramagnetic and obey Curie"s law, thus become less magnetic at higher temperatures.
Ferrofluids are commonly used in loudspeakers to sink heat between the voice coil and the magnet assembly. A strong magnet placed near the voice coil (which produces heat) will always attract colder ferrofluid towards it more than warmer ferrofluid thus forcing the heated ferrofluid away, towards the heat sink. This is an efficient cooling method which requires no additional energy input (4).
Electronic Devices
The fluid of magnetic particles forms a barrier which prevents debris from entering the interior of the hard drive. However, the ferrofluid is still similar enough in properties to a true liquid that it will not interfere with the spinning of the shaft. A small amount of ferrofluid, placed in the gap between the magnet and the shaft, will be held in place by its attraction to the magnet(4).
The other application of ferrofluid:Automotive ,building , optics,…
There are 2 main research areas in magnetic fluids for the future:
1) Spacecraft design
2) Filtering impurities from fusion reactions
Source:
1) http://www.southernbiological.com/Products/Kits&Equipment/SpecialLabFieldEquipt/G80_10.htm
2) http://www.ferrotec.com/products/ferrofluid/bioMedical/applicationNote.php
3) http://www.ferrotec.com/technology/ferrofluid.php
4) http://en.wikipedia.org/wiki/Ferrofluid
