On Sun, 17 Feb 2008 17:42:29 -0600, Terry
> wrote:

>On Fri, 15 Feb 2008 21:49:36 -0500, Kenneth
> wrote:
>
>>In fact, aluminum is used in contact with ammonia in all
>>sorts of industrial applications (most relating to
>>refrigeration) precisely because it is not harmed as would
>>be certain other metals.
>
>Hi Kenneth,
>
>A relevant observation is that there is a huge difference between
>ammonia (NH3, pure gas or pure liquid depending on the conditions, and
>sometimes referred to as "anhydrous ammonia") and what we all commonly
>refer to as "ammonia" which is a solution of ammonia gas in water.
>
><chemistry mode on>
>Ammonia-water solution is basic because ammonia pulls H+ ion off some
>of the water molecules, leaving hydroxide ions (OH-). Not many
>hydroxide ions because ammonia is a weak base, but aluminum definitely
>does not like hydroxide ion. Last's weeks experiment in my lab
>involved the students dissolving granular aluminum in a concentrated
>hydroxide solution.
>
>If there's no water present, which would be the case in refrigeration
>machinery, there's no H+ ion to be pulled off. No problem using pure
>ammonia gas or liquid in aluminum tubing or some such.
><chemistry mode off>
>
>If you find that ammonia works for cleaning your aluminum ware...more
>power to you. Might have something to do with the concentration or
>the length of time or the phase of the moon or some such. It's not
>something I'd try, though.
>
>Best -- Terry
>...I never wanted to be a chemist. I....I....I wanted to be...a
>LUMBERJACK....

Hi Terry,

I thank you for your great comment...

In fact, that was the direction I was going (though
articulated with far less sophistication with regard to the
chemistry) when I guessed that Wayne put the "ammonia" (in
fact a solution of ammonia in water) on the aluminum, rather
than putting it in another container so that its vapor could
act on the pan.

Based on my experience, I believe that if one puts a dish on
the pan, puts some household ammonia solution in the dish,
and seals the whole mess in a plastic bag, the deed will be
done with no damage whatever to the pan.

I don't believe that has anything to do with the phases of
the moon (though I am open to that possibility as I know
less about astronomy than I know about chemistry).

Based on what I have read, I believe that problems can occur
because the of the water in the household ammonia products
rather than the ammonia itself.

With the "put the solution in a dish" method that I have
used, what comes out of the solution is (mostly) gaseous
ammonia, and that does no harm to the aluminum.

All the best,
--
Kenneth

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