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Author Topic: Can liquid metal be magnetised?  (Read 10716 times)

Offline realmswalker

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Can liquid metal be magnetised?
« on: 17/04/2005 02:32:58 »
...or even affected by magnets? (any type of metal, it doesn't matter)

Also, would it be possible to set up a magnetic field which could contain the liquid metal and prevent it from flying back towards the main magnet . Could you, for instance, have a sword blade  made out of liquid metal...


 

Offline Quantum cat

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Re: Can liquid metal be magnetised?
« Reply #1 on: 17/04/2005 12:41:40 »
Only certain metals can be magnetised (it is a common misconception that magnets can attract and be any kind of metal) these metals are called ferromagnetic and have a certain property, to do with their electrons, that means they can be magnetised. The ferromagnetic material forms things called domains which are like tiny magnets, they're collections of atoms whose poles all face the same way. In a normal chunk of the material they will be pointing in random directions, so an overall magnetic field won't happen (they'll cancel each other out) but if they are aligned, there will be an overall magnetic field. Electric fields relate to magnetic fields cand influence each other. You can make a weak magnet with no ferromagnetic material by winding a conducting coil of wire hundreds of times around a cylinder, and putting current through it. This is called a solenoid. If you put a piece of iron (or other ferromagnetic metal) into it, the solenoid becomes a really powerful electromagnet. The magnet disappears as soon as the current stops flowing. (except in steel where it becomes a permanent magnet) The magnetic field of the solenoid makes the domains align with it in the iron which is why it becomes much more powerful than by itself.

If you put some liquid iron in a solenoid: The iron wouldn't be able to form domains as a liquid, because the aroms slide around each other and can't form stable relations with each other. the atoms wouldn't get lasting positions so I don't think a magnet would work. They'd always be moving around. Maybe it would work if the liquid was totally still and sealed in a heat-proof cylinder with a solenoid around it. To get this to be suspended you'd need a magnet above or below it. The slightest movement would destabilise the magnet formed from the liquid iron so not very practical for a sword.

Maybe you could: Melt some steel. Put it in a cylinder. Put a solenoid around it and make the molten steel into a magnet (keeping it perfectly still) Caluclate the strength of the newly-formed magnet. Calculate the distance and the strength of the magnet used to suspend it. Somehow remove the cylinder without disturbing the steel. Voila, a floating length of molten steel. Not very practical for swords though.
 

Offline realmswalker

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Re: Can liquid metal be magnetised?
« Reply #2 on: 18/04/2005 01:21:43 »
well if you were in a 0 gravity area and you had liquid steel floating around would it be attracted to  magnet if it was near it?
 

Offline Quantum cat

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Re: Can liquid metal be magnetised?
« Reply #3 on: 18/04/2005 09:41:47 »
Probably the tiniest force of the magnet would disrupt the liquid and cause it to immediately lose its magnetic properties.
 

Offline Tronix

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Re: Can liquid metal be magnetised?
« Reply #4 on: 18/04/2005 17:39:23 »
still, might be an interesting (if slightly dangerous and very difficult) experiment to see what woudl actually happen...

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Offline gsmollin

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Re: Can liquid metal be magnetised?
« Reply #5 on: 18/04/2005 17:52:48 »
Ferromagnetism is a special property of certain metals with electronic spin-moments similar to iron. This property only exists within a limited temperature domain. Above a critical temperature, known as the Curie temperature, the iron loses its ferromagnetic properties. The Curie temperature for the most common ferromagnetic alloy, 3% silicon steel, is 730 degrees Celsius. The melting temperature is above 1500 degrees C, so the metal would lose its magnetic properties long before it melts. Many ferromagnetic, and ferrimagnetic materials have much lower Curie temperatures than Si-Fe.

I do not know of any materials that retain ferromagnetic properties when hot enough to be liquid. However, the question was more general. It asked if liquid metals could be magnetized. The answer is yes, but the magnetic properties are much weaker than ferromagnetism. Even water can be magnetized, but not permanently. The magnetic polarizations that can be placed within liquid samples are lost within a second or so after the magnetic field is removed.
« Last Edit: 18/04/2005 17:57:03 by gsmollin »
 

Offline Quantum cat

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Re: Can liquid metal be magnetised?
« Reply #6 on: 18/04/2005 22:45:21 »
Aha, there we go, I was wrong :-)
 

Offline DoctorBeaver

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Re: Can liquid metal be magnetised?
« Reply #7 on: 19/04/2005 02:19:33 »
So, you see, you couldn't have captured Terminator 2 with a magnet! heh
 

Offline daveshorts

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Re: Can liquid metal be magnetised?
« Reply #8 on: 19/04/2005 10:36:42 »
You can suspend small iron particles in a fluid, which unimaginatively is called a ferrofluid, in a magnetic field they will align like iron filings. I think they use it to improve the magnetic field strength in some posh speakers. You can make interesting shapes with it but it normally makes hedgehog shapes like:



in the same way that iron filings make hedgehog shapes, but less sharp due to surface tension of the liquid. I think you would have difficulty making swords out of it..
 

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Re: Can liquid metal be magnetised?
« Reply #8 on: 19/04/2005 10:36:42 »

 

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