 |
 |
Super Magnets
Name: N/A
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: 1991
Question:
I would like to know
how super magnets are made. How will they be
used to help us?
Replies:
When I was a kid there was a toy called a "Monster Magnet" which
was basically a couple of bar magnets attached to the ends of a
plastic "horseshoe". It was quite a bit stronger than the regular
magnets I had, and I wonder if it was made of one of the magnetic
alloys like Alnico. I suspect that Nick is asking about magnets
made of such magnetic alloys; "super magnet" would certainly be an
appropriate term.
rcwinther
The title "super magnets" is a very broad description of several
families of rare-earth magnets.
I will start with the common variety of "iron" style magnets.
Most common magnets are made of some alloy, or combination of
elements, of steel. Each of these alloys have different properties
that allow the molecules to be "aligned" North to south. This
property allows the steel to become "magnetic" to different degrees.
These alloys of steel are cast and cooled at a very specific
rate so as not to destroy their properties. Then they are subjected
to a very strong electrical field for a very short period of time
on a special machine with big coils of wire on it, and very large
capacitors that discharge through the coils. The field is created
and collapsed many times over a period of time until the magnetic
field is established.
Some of the most powerful magnets are made of a material called
Neodymium-Iron-Boron (NeoIron), Sumarium Cobalt, and AlNiCo (
(aluminum-Nickel-Cobalt).
Each material has different magnetic properties and strengths measured
by Gauss and Oersteds. Each also has a temperature point at which
the magnetic material looses its magnetic properties. That is called
its Currie point. Generally, the more powerful the magnet, the lower
the Currie point. Superconducting magnets have very low Currie points,
some of them just above absolute zero, and others as high as -100 deg F.
Look at question #74 on the General BB (which did not get answered,
sorry about that, Nick!) It is the same person asking, and there he does say
"superconducting" so I will bet he means "superconducting" here too (good
guess, J.H.!) Besides permanent magnets, there are what are called
electromagnets; these use an electric current to generate a magnetic field.
(You can make one with some wire, a large nail or other piece of iron, and
a lantern battery.) Some machines (like particle accelerators) need enor-
mously strong magnetic fields; it takes a very large electric current to
generate such magnetic fields. As you probably know from experience,
electric current produces heat when it flows through a material. We use
good conductors like copper when we want to minimize this heating; but if
the current is very large, there can be a lot of heating, even with very
good conductors, and this is wasted energy that otherwise would contribute
to the magnetic field. What can we do? Well, it turns out that many
materials lose all resistance to the flow of electric current if they are
cooled to a VERY low temperature (far colder than it ever gets even at the
South Pole); we say that they become superconducting. Then basically no
energy is lost due to heating and all of the electrical energy goes into
producing the magnetic field. For now, only big specialized projects will
use superconducting materials; it would cost much more to use them in
everyday applications than any money that would be saved by using them.
rcwinther
Click here to return to the Physics Archives
| |
Update: June 2012
|
|
