|
Ferrofluid
is a liquid which responds to magnetic fields. As you can see in the
picture (below), if placed near a magnet the liquid will be
attracted as a piece of iron would, and will leap up, forming itself
up into spikes. If you touch the spikes you will find that they have
not skinned over or solidified into these shapes. The spikes are
composed of liquid.
To
understand why the ferrofluid does this, think about the nature of
magnets. For a blob of ferrofluid on a magnet, the whole surface is
one pole - so it tries to repel itself.
To do this, the fluid piles up into the shape which minimises
the amount of pole and puts it as far from itself as possible. If
you do this experiment with an electromagnet you will find that as
the magnetic field increases the spikes will sharpen and increase in
numbers.
Originally
developed for NASA in the '60s as a way of sealing spacecraft parts
in vacuum and controlling liquids in weightlessness, ferrofluids are
now used for a variety of applications.
-
In
top quality speakers, ferrofluids are used to lubricate and cool
the coil, upgrading sound reproduction at high volume. Ferrofluids
allow a speaker to carry more sound volume before heat build-up
causes sound distortion, especially in large speakers like PA
systems.
-
Ferrofluids
are used to make rotary and feed-through seals in industry,
particularly for applications where there will be a pressure
gradient across the seal, e.g. in vacuum pulling of silicon
crystals for the chip industry. A rotary seal is where a shaft
passing from one environment to another must rotate, e.g. a
submarine propeller. A feed through seal is where the shaft must
pull back and forth, e.g. a shock absorber. If there is pressure
or vacuum on one side of the seal, a conventional seal will fail
as the pressure forces out the grease. If the seal is
magnetised, the magnet can hold a ferrofluid in place. Properly
constructed commercial ferrofluid seals are capable of holding
pressures of over 1000psi long term without failing.
-
Increasingly,
ferrofluids are finding use as an educational or artistic
material, especially in conjunction with strong neodymium
magnets, or with electromagnets, which can make the fluids move
in fantastic forms.
Scuddlebutt3
supplies ferrofluid in two kinds (shown below), a hydrocarbon
solvent based version and a water based version. The solvent based
version is the standard. The water based version is only available
in limited amounts and therefore, is not for sale on this website.
|
