Some Curious Uses For Ferrofluids

Beyond holding your shopping list securely in place on your fridge

, magnets offer a host of other practical applications. One of the most interesting magnetic phenomenon used widely in modern industry are Ferro fluids. Ferro fluid refers to a fluid that becomes highly magnetized in the presence of a magnetic field. This fluid is a colloidal substance created by the combination of ferromagnetic particles and a carrier fluid. The particles are so small in Ferro fluids that they will not settle over time, but remain in place as long as a magnetic field is present. Treatment of particles with surfactants prevents them from clumping up, causing the material to remain stable and act predictably.

The most interesting feature of a Ferro fluid is its organization into peaks and valleys when a strong enough magnetic field is present. Under these circumstances, the fluid will take on and retain the appearance of a solid object whose surface is comprised of a cluster of small spikes. In other words, a puddle of dark metallic liquid will transform into a rigid-looking spiked ball or dome when a magnet is placed nearby. The effect is achieved because this shape minimizes the total magnetic energy of the system. This effect is known as the normal-field instability. In its corrugated shape, the magnetic field is concentrated in the peaks. Because the fluid is more easily magnetized than the air, this lowers the magnetic energy, and the fluid seeks this least-resistant formation. Unlike iron ore, ferrofluid holds a shape while remaining a liquid.

This curious property makes ferrofluid useful for a wide array of technological applications. The builders of hard discs often use a small amount of the fluid in spinning drive shafts. Attracted to the magnets placed around the shaft, the ferrofluid seals the opening, preventing foreign objects from entering. In conjunction with powerful magnets, ferrofluids have friction-reducing properties, useful for some mechanical applications where it is desirable that a magnet glide unimpeded across a surface. In medicine, different kinds of this fluid are used in Magnetic Resonance Imaging or MRI machines for the detection of cancer and other anomalies. NASA has experimented with using Ferro fluid in its altitude control systems.

One common use for Ferro fluids is in loudspeakers. Placed around the voice coil and held in place by the speaker's magnet, they help divert heat toward heat sync, acting as a coolant without expending extra energy. Optic and heat transfer applications are also being researched. Many devices or systems that use magnets gain an advantage by combining with Ferro fluids and taking advantage of their particular physical properties. Some museums have designed and built fountains and other features that display this curious material for the enjoyment of its visitors.

by: Marie Winston

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