Hydrogen gas produced when machining al.

[Tarlo]

I was told recently that machining aluminium produced Hydrogen gas, as the material oxidises. I was told this by a salesman, so i am not sure of the truth in it... If anyone could enlighten me?

 

[kenvlach]

True, with aqueous cutting fluid.
And if chemically machining the Al with hot caustic (NaOH solution), the aluminum oxide dissolves as fast as it forms, allowing continuos exposure of bare Al to H₂O, thereby producing a steady stream of H₂ which can ignite under certain conditions, as when using a foam blanket to cut down on noxious mist.

 

[Tarlo]

Thanks Kenvlach, The machine is a high speed machining centre that uses ethanol as a cutting lubricant, I just wonder if the Hydrogen gas is as big a threat as the ethonol?

 

[kenvlach]

Al can thermodynamically take O away from CH₃CH₂OH. Might strip off the entire hydroxyl (-OH), leaving an ethane radical. Two radicals could combine, producing butane CH₃CH₂CH₂CH₃.
But, a more likely reaction mechanism: the OH end of the ethanol adsorbs onto the Al and then dissociates, with the O sticking to the Al and the H replacing the OH on the former ethanol molecule, producing ethane gas C₂H₆ rather than H₂.
But, not very much in either case; maybe only forming a monolayer or two per cutting pass.