welding gas to preserve finish

[qwertyu]

Question for those who use welding gas in their finish cans - can standard mig gas be used? It isnt pure argon so I am not sure

[ian]

As far as i know, welding gas is a mix of Ar and CO2, or Nitrogen and CO2.
I can see no chemical reason why the argon/CO2 mix can't be used.
I'm less sure about the nitrogen / CO2 mixes as I'm not sure what role Nitrogen plays in hardening a finish.

[qwertyu]

Ive just done some reading and it seems like nitrogen is lighter than o2 therefore in a can o2 will be in contact with the finish.

I might just go with the total tools mig gas which they say is argon/co2/o2 therefore should be suitable

[AJ.]

Ive just done some reading and it seems like nitrogen is lighter than o2 therefore in a can o2 will be in contact with the finish.

I might just go with the total tools mig gas which they say is argon/co2/o2 therefore should be suitable

Based on that theory, the Argon is the heaviest so if the gases do seperate the Argon would be the gas in contact with the finish, which being an inert gas I presume would be ideal. Edit ** if I had of thought before typing I wouldn’t have confused Nitrogen and CO2, CO2 would be the heaviest.

If I remember my periodic table correctly Nitrogen has an atomic mass of 7, Oxygen is 8 and Argon is 18.

A normal mig gas is usually 75% Ar, 20 odd percent CO2 and just a hint of Oxygen.

Cheers Andrew

[ian]

Dredging my memory of basic chemistry (again)


Finishes dry -- more accurately cure (?) -- through a combination of solvent evaporation and a chemical reaction between the finish and oxygen from the air.
I don't know if any finishes utilise Nitrogen in the chemical reactions, but I'm pretty sure that no finish utilises Carbon Dioxide in the curing reactions.

When a finish can is mostly full, a mix of 75% Ar, 20% CO2 and about 5% O2 (the composition of Total Tools' MIG gas), shouldn't be too much of a problem. But with a half full can of finish, at 5% O2 there is probably enough oxygen to start the finish's curing reaction. I suspect that within a part full can of finish topped with "welding gas" Brownian motion of the gas and vapour molecules will not really allow the different gases to settle into "layers" with the Argon in contact with finish surface. However, the 5% concentration of O2 might be low enough for the O2 / finish reaction to "stall" before too much finish has cured to a hard state.

[jack620]

Ive just done some reading and it seems like nitrogen is lighter than o2 therefore in a can o2 will be in contact with the finish.

If that was true wouldn’t we all be breathing 100% O2?

[ian]

If I remember my periodic table correctly Nitrogen has an atomic mass of 7, Oxygen is 8 and Argon is 18.

A normal mig gas is usually 75% Ar, 20 odd percent CO2 and just a hint of Oxygen.

Andrew, you are remembering your Periodic Table "correctly" but you are recalling the number of protons rather than the atomic mass.

Nitrogen has 7 protons and 7 neutrons -- for an atomic mass of 14 (near enough). but it travels around as dinitrogen (N2) so its apparent mass is 28.
Oxygen (O2) has an atomic mass of 32.
CO2 has an atomic mass of 44.

Argon with an atomic mass of 40 (again near enough) is a noble gas and thus travels around as single atoms.