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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



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