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I am currently experimenting with simple methods of metal casting at home. It is conventional wisdom that magnesium is better left to the professionals due to the unfortunate arrangement of its combustion and melting temperatures. I dont have access to any inert gasses or vacuum furnaces; but like a challenge.

The first thing that occurred to me was to use CO2 cylinders you can buy at the supermarket to protect my casting area. Luckily I didnt try that experimentally, since it is a known bad idea. Same applies to water vapor. Molten magnesium will happily steal the oxygen from either, leaving carbon resp. hydrogen gas behind. And a lot of heat of course.

Which brought me to the following counter-intuitive idea: if magnesium cares so little for carbon or hydrogen, could you protect your magnesium from burning with hydrocarbon gas? If I douse my casting mould in butane, then pour my molten magnesium in, I am likely to set the butane ablaze, sure. But I can deal with that; as long as my magnesium stays put.

Is this the dumbest idea ever? Or might it actually work?

To make my question more concrete: what is the known chemistry of magnesium at 700c and pure hydrocarbons? Note that there will also be a lot of silicon dioxide present, which can form a thermite with magnesium, but normally shouldn't under these circumstances. But perhaps the hydrocarbons could catalyze that reaction?

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    $\begingroup$ It's a dumb idea. If you insist, at least use Argon, cheaply available as welding gas. $\endgroup$
    – Gert
    Commented Dec 31, 2017 at 16:49
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    $\begingroup$ It is a dumb idea. // Do not try this using argon gas. Yes argon should blanket the magnesium assuming you have the right equipment which you don't. This isn't a "challenge," rather it is playing Russian roulette. $\endgroup$
    – MaxW
    Commented Dec 31, 2017 at 16:53
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    $\begingroup$ You said: "I am likely to set the butane ablaze, sure. But I can deal with that; as long as my magnesium stays put." But, can the others in your apartment store, deal with that, too? Sounds not only dangerous but also careless. $\endgroup$
    – Gyro Gearloose
    Commented Dec 31, 2017 at 16:56
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    $\begingroup$ Thanks for all the folk wisdom so far; still a bit short on arguments based in chemistry though ;) $\endgroup$
    – Eelco Hoogendoorn
    Commented Dec 31, 2017 at 17:03
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    $\begingroup$ You're "prepared" for a worse case scenario of an explosion of burning magnesium? How the !@#$%^ are you going to put it out if some gets on you? $\endgroup$
    – MaxW
    Commented Dec 31, 2017 at 17:13

1 Answer 1

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if it might pull the oxygen out of sand , try using magnesium oxide, surely it won't pull the oxygen from its own self. Or using burnt lime, surely it won't pull oxygen away from calcium. It might react with butane to form magnesium hydride and carbide ....which would be fun to play with 😊. Also magnesium easily reacts with nitrogen to make the nitride...which is an excellent way to make ammonia 👍

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  • $\begingroup$ Not sure those make good mould materials; not without water but that's not a option. Apparently carbides and hydrites don't form in the reaction with co2 or water; are you aware of any particulars of these compounds that might be relevant to the situation? $\endgroup$
    – Eelco Hoogendoorn
    Commented Dec 31, 2017 at 22:20
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    $\begingroup$ This is a largely nonsense answer. $\endgroup$
    – Gert
    Commented Dec 31, 2017 at 22:27
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    $\begingroup$ Magnesium most certainly CAN form a carbide when heated with a hydrocarbon! ! $\endgroup$
    – Shannon Dove
    Commented Jan 11, 2018 at 19:08
  • $\begingroup$ gert is the one full of nonsense $\endgroup$
    – Shannon Dove
    Commented Jan 11, 2018 at 19:09
  • $\begingroup$ You'll likely decompose the hydrocarbon. $\endgroup$
    – Oscar Lanzi
    Commented Aug 9, 2020 at 15:49

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