A question for all you chemists out there...

Seems like I should be able to find this with skyn...I mean google, but alas I had no luck. At what temperature at sea level does gaseous C02 separate into Oxygen and Carbon? Please, please let the answer be above 2k°F

393 kJ/mol is required amount of energy to turn CO2 into into graphite and O2, but that is at standard conditions.

I saw a page that says above 1500 K disassociation is prevalent - that is 2240 F, but I'd have to think too hard about thermodynamics to answer this right now.

mind us asking why you need to know this? and why above 2k°F is good?

I want to use CO2 to remove gas impurities from molten aluminum used in my metal casting adventures. In theory, it will bond with these impurities when bubbled thru the melt. My fear is that if the CO2 splits up under about 1700° (approx temp of my melts), the released pure-ish O2 will burst into flames, tossing molten Al all about and possibly igniting an aluminum thermite reaction.

link

Here's one take on how to remove gas impurities from molten aluminum.

What gasses are you trying to remove? Where do they come from? Are they present in the Al you start with or are they introduced by your process or from the air?

I have no idea about metal casting - just interested.

Hydrogen is introduced into an aluminum melt when an overly oxidising atmosphere (lean flame) is created in the foundry furnace. This atmosphere creates aluminum oxide, referred to as "dross" or "slag". A neutral atmosphere can eliminate most of this dross, but not completely prevent it.Dross creation disolves Hydrogen into the melt, which if introduced in a high enough concentration, will cause inclusions (gas pockets) in the finished piece. A good casting relies on as pure a melt as possible. Too many gas inclusions can really cause problems if you need exacting results in your castings - I.E. castings requiring final milling in a lathe or other machine.

Heres an excerpt from an online tutorial posted in another forum I frequent for DIY metalcasters:

Very smart metal caster guy said: Degassing Certain metals dissolve gas in their liquid state, such as aluminum, which dissolves hydrogen. If the gas is not removed, it will come out of solution on solidification and create gas bubbles in the casting. There are two primary methods of removing gas: mechanical agitation and chemical reaction. Mechanical methods generally bubble an inert gas through the melt, releasing the dissolved gas much like shaking a soda would release carbon dioxide. Simply stirring the melt can remove some gas (often noticeable on heavily fluxed aluminum melts as little pops of flame when the melt is agitated—since salt fluxes dissolve steam readily, they promote hydrogen dissolution into the melt), but rarely removes all of it, and can introduce other contaminants like iron. The other method, chemical reaction, adds a material to the melt that the dissolved gas will react with. In the case of aluminum, bubbling chlorine gas through the melt will remove hydrogen as HCl gas.

I could use a bit of chlorine "pool shock" to degas the melt, but this puts off chlorine gas (not too yummy) and I will be melting in a reasonably enclosed area this winter since it gets pretty cold in Ohio. If possible,Id like to use CO2 as I can get those little bike inflator cartridges for ridiculously cheap, and CO2 wont try any harder to kill me than any of the other foundry related activities I'll be partaking in. Chlorine gas on the other hand doesnt like my physiology quite nearly as much, and it will almost certainly win if it and my central nervous system decide to have a lil arm wrestling match

For some reason I have a CRC Handbook of Chemistry and Physics and a Merck Index at home on a bookshelf.

My Merck Index states that CO2 gas is not affected by heat until the temperature reaches about 2000 degrees.