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Elimination of Al outgassing when exposed to steam

Hello. I'm an engineer (with minimal metal finishing experience) trying to design a sealed, pressurized chamber that will contain pure steam (no other gasses), and that will have zero outgassing over a period of roughly 5 years. Currently, copper chambers are used since copper doesn't react with water, but we would like to go to Al or Magnesium for weight improvement. I was curious as to what kind of coating could work for this application (i.e. anodizing or Ni plating).

On a side note, is there a commercial Cu deoxidizer anywhere, and what is its trade name? Thanks much.

Ben Broili
- Washington
2000

Unless you can define "zero outgassing", the answer is difficult. Is it in ppm or ppb?

Outgassing will depend on surface smoothness as well as surface chemical reaction with steam. If the surface is nonreactive with steam and extremely smooth, and the steam is flowing continuously, eventually the contamination will diffuse out over a period of time to extremely low levels (<ppb). Also, if the surface gets passivated with steam, the same will result.

I have a gut feeling that low porosity mirror-like thin nickel plating would work, although aluminum also forms natural oxide that could provide the same effect. However, the steam flow should not wear the surface and remove surface atoms layer by layer.

Mandar Sunthankar
- Fort Collins, Colorado
2000