beergod - 7-5-2011 at 14:49
There has been a little bit of talk about generating hydrogen from aluminum/gallium alloys... The thing is gallium is a little expensive.. One
researcher uses 20%/80% gallium/aluminum to keep the aluminum reactive. Seems like that ratio might be a little high, you only need just enough
gallium to prevent the oxidation, so could 1% work also?
Can anyone speculate on the minimum amount of gallium in an aluminum/gallium alloy required to keep the aluminum reactive?
not_important - 7-5-2011 at 15:36
You're not preventing oxidation, you're encouraging it with the gallium. The surface layer of Al2O3, dry or hydrated, slows down further oxidation.
Gallium or mercury cause defects in this surface, allowing oxidation to continue. An old demo was to paint a little solution of a mercury compound
onto a piece of Al, which would then oxidises away with the growth of a powdery growth of Al2O3. This is also the reason shipping gallium by air is a
hassle, it penetrates Al and its alloys, weakening the inter-grain boundaries and allowing oxidation of the bulk metal.
So you need enough gallium to insure that a coherent layer of Al2O3 does not form. As some of the gallium gets trapped in the oxide flaking off the
bulk Al, you need enough of it to always be interfering with the formation of good quality films of Al2O3.
Don't know the minimum required, from what I've read it is a fairly large proportion. This might be of interest: http://www.slideshare.net/cimon9999/e-keane-journal-paper-on...
and this one as well
http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/alumin...
[Edited on 7-5-2011 by not_important]
Sedit - 7-5-2011 at 17:18
Can Gallium salts not be used simular to how HgCl2 is used to lower the requirments of Mercury needed.
beergod - 14-5-2011 at 13:25
Well it seems industry standard is 20% gallium 80% aluminum. Anything less will give very unsatisfactory results.