Ferro- and Magnetorheological fluids
October 27, 2009, 11:13 am
Filed under: technology | Tags: ,


A ferrofluid,  is a liquid which becomes strongly polarised in the presence of a magnetic field. They are colloidal mixtures composed of a nanoscale ferromagnetic, or ferrimagnetic, particles suspended in a carrierfluid, usually an organic solvent or water. The difference between ferrofluids and magnetorheological fluids (MR fluids) is the size of the particles. The particles in a ferrofluid primarily consist of nanoparticles which are suspended by Brownian motion and generally will not settle under normal conditions. MR fluid particles primarily consist of micrometre-scale particles which are too heavy for Brownian motion to keep them suspended, and thus will settle over time due to the inherent density difference between the particle and its carrier fluid. These two fluids have very different applications as a result. Ferrofluids are used to form liquid seals around the spinning drive shafts in hard disks. The rotating shaft is surrounded by magnets. 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. The fluid of magnetic particles forms a barrier which prevents debris from entering the interior of the hard drive. Magnetorheological fluids are used in the shock absorbers of a vehicle’s suspension are filled with MR fluid instead of plain oil, and the whole device surrounded with an electromagnet, the viscosity of the fluid (and hence the amount of damping provided by the shock absorber) can be varied depending on driver preference or the weight being carried by the vehicle – or it may be dynamically varied in order to provide stability control. This is in effect a magnetorheological damper.

watch it in action here

via:: wikipedia


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