Aluminum corrosion?

[Pentaquark]

Gentlepeople,

I borrowed a 7.5G aluminum kettle from a friend to do my boil in. I'm a lazy man and I didn't quite 'clean' the kettle the same day. I more 'rinsed it out and left it with my copper wort chiller and about a foot of standing water in it' overnight. Now when I pull the chiller out and go to actually clean the thing, there's little black, spidery corrosion marks all over the pot that won't go away with standard dish soap and elbow grease.

Has anyone experienced anything like this? Any thoughts on removal? I feel pretty bad that I marred my friend's kettle since he was kind enough to let me borrow it.

[mpeck]

Bar Keeper's Friend? I found this on using it for aluminum:


Aluminum: Bar Keepers Friend may be used on aluminum, but with certain reservations. Bar Keepers Friend should not be used on anodized aluminum. Anodized aluminum is often colored or has a decorative finish. Under no circumstances use Bar Keepers Friend on such aluminum finishes. However, Bar Keepers Friend can be used on aluminum doors, windows, pans, etc., which is usually not anodized. Just remember, if the aluminum is colored, DO NOT use Bar Keepers Friend. Also, do not use alkalis (ex. ammonia, lye, washing soda.) on aluminum.

[Frank]

there's little black, spidery corrosion marks all over the pot

Aluminum is one of the most highly corrosion resistant metals out there especially environmental and water based corrosion. When aluminum corrodes it actually pits and the surface becomes irregular. Without seeing it first hand I would suspect that you are seeing the oxide film start. This is a good thing and I would not suggest scrubbing it off to make the kettle "shinny" again. The oxide film will turn the aluminum a dull grey to black color, this actually protects the metal from corrosion and makes the metal lest reactive to substances (such as lower ph liquids like wort). What happens is oxygen bonds to the surface making aluminum oxide. There is a strong school of thought in brewing to actually hasten the formation of this oxide layer by boiling a full pot of water before ever using it with wort.

Aluminum's appearance is dulled and its reactivity is passivated by a film of aluminum oxide that naturally forms on the surface of the metal under normal conditions. The oxide film results in a material that resists corrosion. The film can be thickened using electrolysis or oxidizing agents and aluminum in this form will resist attack by dilute acids, dilute alkalis and concentrated nitric acid. http://www.chemicool.com/elements/aluminum.html

"Oxidizing agents" = Oxyclean
"dilute acids"= Wort

[mymead]

the cheap and easy thing to do is mix 1/4 cup table salt and 1/4 cup backing soda add alittle water to make a thick paste.
scrub (affected area only) with soft spunge, rinse with soap and water. Then fill pot 1/4 to 1/2 full of water and boil for 20min. This should remove the marks and stop the reaction in the metals, plus reseal the aluminum patina.

Atlest this is what Grandma used to do. But then AL. pots are not the same as back then.

Or jus some PBW with Oxiclean.

Next time, remember to never let copper set in water over night. The Mg in the copper brakes down forming salt and a small current(you made a battery) and in this Stainless Steel pots doesn't even stand a chance. i have aways found it best to clean and dry your copper parts as fast as possible and never store them in contact with other metals.

[fergmeister]

FYI: How to brew has an appendix on metalurgy and you can contact Palmer @ www.howtobrew.com
Chuck

[cyburai]

http://www.howtobrew.com/appendices/appendixB-2.html

Its called galvanic corrosion.. read up and look into verdegris for the green toxic corrosion on the copper side

[Steve Brown]

This thread is a great example of why LBG is such a great group and how brewing can teach us everything. Metallurgy. Biology, Chemistry. Bio-chem. Plumbing, electricity, physics, gastronomy, - is there an end?