Quince
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Dissolving rust without damaging Al?
All the metal in my computer's cooling system waterblocks is aluminum, but for the tank itself I used (intended to be temporary) a large coffee tin
can. I thought it would be fine, because it looked like the inside was coated. Turns out the antifreeze I put as anti-corrosive agent in the water
dissolved the coating, and the can got all rusty... the tubing is covered on the inside with tons of brown. I could flush with HCl and that would
probably clear out the rust, but I'm afraid it will damage the aluminum significantly. What else can I do? Manual cleanup is not an option, as the
system is fairly involved (six waterblocks, splitters, etc.).
\"One of the surest signs of Conrad\'s genius is that women dislike his books.\" --George Orwell
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mantis
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try it with acetic acid, vitamine c, oxalic acid, etc.
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Mr. Wizard
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Why not go to an auto parts store and buy some radiator flush? IIRC they did contain some Oxalic Acid which dissolves rust. The positive side to this
is the automotive products are designed to not attack aluminum radiator and cooling system parts. Good luck ;-)
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Quince
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I never knew vinegar dissolves rust. LOL, vitamin C... yeah, I've got gallons of that! 
Thanks for the suggestions.
\"One of the surest signs of Conrad\'s genius is that women dislike his books.\" --George Orwell
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Fleaker
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I'd say the best bet is oxalic acid since I'm pretty sure that they took the oxalic acid out of radiator flush (over toxicity concerns? sheesh).
Couple hours and it will all be rust free, courtesy of coordination chemistry
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DrP
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Tannic acid, phosphoric acid and oxolic acids are all used in common rust conversion products. I converted some rust with phosphoric acid, but tannic
is supposed to be better (not sure how to source it though).
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12AX7
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For tannins, just boil some oak bits -- leaves, twigs, bark, acorns. This time of season, buds and twigs would be easiest. Galls, those little
parasitic balls on leaves, have a lot in them too. Oak tea turns black with a mere dash of iron ions, so...
To isolate say, gallic acid, you'll probably have to saponify the tannin esters, then acidify to release the relatively insoluble gallic acid
(3,4,5-trihydroxybenzoic acid). There are other groups in tannins that contain gallic acid but I don't remember how to seperate them. Note that
tannins are at best indefinite compounds, usually with high MW.
Doesn't seem to me tannins would be very useful for desolving, though. The iron solution is pretty well black, but I don't know if that tends to be a
sol of precipitate or what.
Tim
[Edited on 4-18-2006 by 12AX7]
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