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How do you melt magnesium without causing its combustion?

I own a foundry capable of reaching temperatures around 2000 °F, and I recently bought some magnesium for melting before doing my research. I cannot find any information on how this process works or if it is even possible.

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    $\begingroup$ You'd have to do it with an inert atmosphere (no oxygen). It would require specialized equipment. $\endgroup$ – MaxW May 12 '17 at 0:14
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    $\begingroup$ As MaxW noted, you will need an inert atmosphere within specialized equipment. Just as a note, magnesium auto ignition temperature is 746K (from Wikipedia) so you have an increased safety concern not only when you are melting but during any time the molten metal is above this temperature. $\endgroup$ – J. Ari May 12 '17 at 1:22
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    $\begingroup$ I'm not sure what your foundry is made of, but if it forms intermetallic compounds or alloys with the magnesium (which I strongly suspect it does), you have even more problems than just combustion. Do some research and as other comments imply, get the right stuff. $\endgroup$ – Oscar Lanzi May 12 '17 at 2:18
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    $\begingroup$ Also note that water can't extinguish magnesium fires. In fact just the opposite. Water causes magnesium fires to flare. $\endgroup$ – MaxW May 12 '17 at 3:29
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    $\begingroup$ chemistry.stackexchange.com/questions/16640/… $\endgroup$ – Mithoron May 12 '17 at 14:19
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I have seen molten magnesium; it was covered with charcoal and other fluxes and in a furnace that had a gas shroud. (I think methane that burned any oxygen that got into the shroud atmosphere.) When an immersion thermocouple was put into the magnesium, the open spot immediately burst into flames. I recommend that you not try to melt magnesium; you certainly must get more information than you can get on the internet.

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  • $\begingroup$ This is not Plausible. Magnesium reacts with carbon dioxide and carbon monoxide to form magnesium oxide and carbon. Further Magnesium forms carbides (specifically acetelyides). Charcoal and related gases cannot effectively shield magnesium $\endgroup$ – A.K. Sep 11 '18 at 1:58
  • $\begingroup$ It was a dark granular material ; it may have been a mineral flux ,not charcoal. $\endgroup$ – blacksmith37 Sep 12 '18 at 3:34
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Magnesium is best melted under a flux – these fluxes are normally based on magnesium chloride, with additions of barium-halogen compounds. Obtaining the flux could be difficult due to the toxicity of the barium compounds – it is even difficult to obtain when you are in the industry like myself.

Another option is a reactive cover gas like $\ce{SF6}$ or R134a, however these are expensive, and are extremely bad greenhouse gases.

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As with any science, advances are made by doing something stupid or accidental - the key is being able to do something intentionally stupid safely enough to do it again. That being said, wear proper safety gear - flame retardant clothes, blacksmithing gloves, a full face shield (i.e welding mask) not just safety goggles from a home improvement store. Once you're pretty sure you're not going to get hurt, then you can proceed.

Before you begin, you should know that this is not the cheapest way to do this, nor the most efficient, but it is effective, and will produce results you're looking for.

You will need:

  • A crucible (an old/empty steel fire extinguisher with the top cut off will work great)
  • Inert gas (you can almost always find some locally, but do your research first to find pricing and proper storage of it)

Find an extra-tall, nonporous crucible (steel should be just fine), and place it in the cold foundry, making sure it has a sturdy base. Add the magnesium into the crucible, and fill to the top with argon. Begin heating up the foundry and crucible. Argon is heavier than air, so it will push the air out as it fills the container, which if you're using a charcoal foundry, will be evident by a ring of charcoal around the crucible momentarily going cold as the argon replaces the oxygen. At this point, sit back, and go about the melt like you would anything else.

If you're casting it, the trick is getting the mold to be encased in an argon bath as well, for that you will need a much larger container and a lot more argon.
Look into how they melt titanium – it has all the same issues.

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