Ferrofluid

 

Developed by NASA scientists in the 1960s, ferrofluids have the properties of a liquid and the magnetic properties of a solid.

They actually contain fine particles (10-20 nm) of a magnetic solid suspended in a liquid medium.

The benefits of magnetic fluids became immediately obvious: the position of the fluid can be precisely controlled by applying a magnetic field, and by varying the field strength, the fluid can be forced to flow.

Scientists prepared ferrofluids containing fine particles of ferromagnetic metals such as cobalt and iron, and magnetic compounds such as manganese-zinc ferrite. However, so far most of the work has been carried out on ferrofluids containing Fe3O4 magnetite nanoparticles.

The fluid medium of choice is kerosene for educational research or simple experiments, and synthetic oils for professional use.

While the characteristic spike pattern on the ferrofluid surface is spectacular, this property is not particularly useful. However, ferrofluids have found a wide range of applications, including, for example, in rotary shaft seals. Ferrofluid can behave like a liquid O-ring as the rotating shaft enters the low or high pressure chamber. The ferrofluid is held in place by permanent magnets and creates a tight seal, eliminating most of the friction produced in a traditional mechanical seal. These rotary shaft seals can be found in rotary anode X-ray generators and in vacuum chambers used in the semiconductor industry. Ferrofluid seals are also used in high-speed computer disks to eliminate harmful dust particles or other contaminants that can cause data reading heads to collide with the disks.

Another use of ferrofluids is to improve speaker performance. In a loudspeaker, electricity is transmitted through a coil placed in the center of the circular permanent magnet. The magnetic field induced by electricity causes the coil to vibrate and thus produces sound and heat. The bath of the electric coil in the ferrule, which is held in place by circular permanent magnets, suppresses unwanted resonances and also provides a mechanism for dissipating heat from excess energy supplied to the coil. Both of these factors lead to an overall improvement in sound quality.

Finally, there is great hope for future biomedical applications of ferrofluids. For example, scientists are trying to design ferrofluids that can transport drugs to specific places in the body using applied magnetic fields. Another ongoing work concerns the use of ferrofluids as contrast agents for magnetic resonance imaging (MRI).