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I'm sorry if this has already been asked but I could not find it on a search here though I also could not determine how to search for the presence of two words ('ammonia' and 'aluminum')

I've read mixed results about whether using household ammonia on aluminum is damaging or not. In my case I want to use it to clean baking trays by putting some (~ 1 tablespoon to 1/4 cup) ammonia on the pan and cover it with a plastic bag and set it aside for hours or a day or so to allow it to soften the baked on grime. I also want to and am using it for a variety of other household and tinkering projects. I read on one site that it is a very bad idea to use ammonia on an aluminum bike frame because it will severally weaken it.

Does household ammonia damage aluminum?

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    $\begingroup$ Why the down votes? Please let me know $\endgroup$ – Ack Apr 18 at 17:47
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    $\begingroup$ I don't know the answer, but my guess is that it would be OK. // The gist is that ALL aluminum forms a surface coating of $\ce{Al2O3}$. Concentrated lye solutions (lots of $\ce{OH-}$) will dissolve that layer. So a lye based oven cleaner would be a definite NO. // Chemistry is an experimental science. Try a piece of aluminum foil in the diluted ammonia solution and see how that results. $\endgroup$ – MaxW Apr 18 at 18:23
  • $\begingroup$ What exactly is household ammonia? $\endgroup$ – Karl Apr 18 at 20:57
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    $\begingroup$ @Karl Household ammonia is just ammonia water, typically sold as a cleaning aid in grocery stores in the USA. I don’t remember the concentration, but you know when you take the cap off the plastic bottle! $\endgroup$ – Ed V Apr 19 at 1:04
  • $\begingroup$ @EdV Found a data sheet for a Walmart product, it´s 2%. But what for? I mean I´m a chemist, and I never looked at some mess in my kitchen and thought "for this I need ammonia". ;) $\endgroup$ – Karl Apr 19 at 8:25
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Yes, aqueous ammonia is likely damaging in time to metal Aluminum in the presence of air and any salts (from outside dust,...) that may further serve as an electrolyte.

Ammonium salts, themselves are good in transporting solvated electrons, and here you are, unintentionally, likely creating a metal-air battery scenario.

Possible half-cell reactions:

$\ce{ Al -> Al(3+) + 3 e- }$

$\ce{ O2 + 2 H2O + 4 e- -> 4 OH- }$

Resulting in a net cell reaction of:

$\ce{ Al(3+) + 3 OH- -> Al(OH)3 }$

The aqueous ammonia may also assist here in the removal of the Aluminum hydroxide by forming a "dissolved/peptised/supersaturated hydrated alumina" (per a paper 'The Precipitation of Aluminium Hydrous Oxide and Its Solubility in Ammonia' by Prideaux and Henness).

In essence, Aluminum is now a more rapidly corroding anode.

Nice experiment, albeit, unintended.

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  • $\begingroup$ "Ammonium salts, themselves are good in transporting solvated electrons,.." Yes, In liquid ammonia!! $\endgroup$ – Karl Apr 19 at 8:18
  • $\begingroup$ Karl: Check out the electrolyte in some commercial battery cells. See chlorine.americanchemistry.com/Science-Center/… to quote: "When ammonium chloride is used as an electrolyte in a battery, it is made into a watery paste and placed between the cathode and anode." $\endgroup$ – AJKOER Apr 19 at 14:41
  • $\begingroup$ I have never heard of a battery in which the electrolyte needs to transport electrons. Except as an overcharge safety mechanism in modern Li-ion cells. Which are definitely and perfectly anhydrous inside. And that webpage you link is an insult to the readers intelligence, sorry. $\endgroup$ – Karl Apr 19 at 16:41

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