Smaller and more powerful than the conventional, 'neo' magnets may capture half the world market for permanent magnets by AD 2000
THE 'movers and shakers of modern
technology', magnets attract little
notice. Now a quiet revolution is underway, with the discovery of new materials
that could provide greater magnetic
potency in smaller packages. The discovery of 'neo' magnets by Sumitomo
and General Motors in 1983, strongly
influenced modern technology. Made
from a compound of iron, neodymium,
and boron, these levitating magnets are
10 times more powerful than ferrite
magnets, and over 100 times as powerful
as steel magnets.
The development of neo magnets is
the latest step in a series that stretches
back to the time of Plato. The only
material known to humans at that time
was lodestone, or magnetite, an oxide of
iron with the formula Fe304, Magnetite
continued to be used as a material for
permanent magnets until the early 18th
century, when strong magnets made
from carbon steel were first produced in
the UK. Advances in steel-making in the
19th and early 20th centuries led to the
discovery of alloy steels. Steel magnets
were surpassed in the 1930s by iron-
based magnets and hard ferrites were
introduced in the 1950s.
But the most exciting advance was
the introduction of rare-earth magnets
in the 1970s and 1980s. The unsur passed coercivities and
energy product of these
materials meant that
small magnets could do
the same job as the
much larger ferrites.
Applications of these
magnets in motors and
other devices began to
grow rapidly. Still, the
high cost of these early
rare-earth magnets limited their use mainly to
military applications.
They also found a niche
in small commercial
products such as wrist watches, where the
amount of material
needed is so little that manufacturing
costs predominate over raw material
costs. A typical quartz watch, for example,
contains a rare-earth magnet of barely
two to three millimetres in diameter.
When used in conjunction with
magnetically sensitive electrical elements, these magnets make possible a
variety of systems for monitoring position, velocity, torque, and other aspects
of automotive, aircraft, and industrial
control systems. A car's cruise control,
for example, relies on such magnets. By
retaining information about the direction of a magnetising field, tiny magnetic
particles store most of the world's data
including personal information on
credit and ATM cards, movies on video-tape, and information on a computer's
hard disk.
Neo magnets are now rapidly
replacing the earlier cobalt-samariurn
rare-earth magnets in many applications. They are also opening up new
applications for permanent magnets,
such as in high-power electric motors,
that had previously relied upon electro
magnets. The dramatic rise in coercivity
and energy production has allowed
substantial reduction in the size and
weight of motors and speakers.
The technology on which neo magnets
have probably exerted the greatest
impact is that of electric motors. Neo
magnets have allowed the construction
of efficient 1,000 hp motors that are five
times lighter and smaller than traditional
motors of the same power. In magnetic
resonance imaging systems, the best
permanent magnet so far is the neo.
Generating a magnetic field of 0.2 tesla
requires 21 tonnes of ferrite magnets
but only 2.6 tonnes of neo magnets.
However, neo magnets have their short-comings, such as a low resistance to corrosion, a rapid decrease in performance as temperature rises and a relatively high cost.
Where material cost remains the
dominant consideration, ferrite magnets are used. But for a rapidly growing
fraction of magnet applications, neo
magnets are being chosen to do the job.
The production and use of neo magnets
has grown rapidly. If the trend continues, neo magnets will account for
close to half of the permanent magnet
market by 2000. The multitude of
magnets that enhance our daily lives
remain hidden. Yet, magnets are
ubiquitous, providing the steady
magnetic fields that exert force on
current- carrying wires to make electric
motors spin and loudspeakers blare.
Magnets are thus literally the movers
and shakers of modern technology.
And neo magnets will be more often
doing the moving and shaking from
now on.
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