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?