Aluminum in methanol, a modest test
Gregory Milligan
The reactions of alcohols with metals (including aluminum) can
be unpredictable. Most metals are coated with a thin layer of oxide,
which protects the surface from attack by the alcohol. In order for the
reaction to start, the oxide coating must be disturbed, exposing fresh
metal. When chemists _want_ the reaction to happen, we often file, scrape,
cut, sandpaper, or otherwise mangle the metal in order to break the oxide
layer.
I have not reacted aluminum with methanol before, but I have
reacted aluminum with isopropanol. As I recall, sandpapering and heat-
ing were required to start the reaction, but once it started, IT WENT!
An undisturbed piece of foil might rest comfortably in methanol without
noticable deterioration, but if corrosion ever started someplace, I bet
it would go pretty fast after that.
Another factor might be water content of the methanol. Methanol
is very good at sucking up water from the air, and that might affect
the rate of corrosion. Offhand, I don't know if water would accelerate
or hinder corrosion.
Greg
Mike Smith
> The reactions of alcohols with metals (including aluminum) can
>be unpredictable. Most metals are coated with a thin layer of oxide,
>which protects the surface from attack by the alcohol. In order for the
>reaction to start, the oxide coating must be disturbed, exposing fresh
>metal. When chemists _want_ the reaction to happen, we often file, scrape,
>cut, sandpaper, or otherwise mangle the metal in order to break the oxide
>layer.
This was a freshly cut piece of foil and should have had an exposed metal
surface at the cut edge; but your point is well taken. I will modify the
test procedure by cutting the foil a couple of times while in the methanol.
(The methanol should then have a shot at the cut surface before the
air can start to oxidize it.)
The experiment was started with more or less water free methanol. It
should gain water from the air over time, so I would expect that if a
reaction was helped or hindered by water we should have both conditions
at some point and the reaction should begin.
How hot did you have to heat it to get the AL to react with isopropanol?
Hotter than an engine compartment?
--
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John G. De Armond
>In article <68...@blake.acs.washington.edu> mill...@blake.acs.washington.edu (Gregory Milligan) writes:
>> The reactions of alcohols with metals (including aluminum) can
>>be unpredictable.
>This was a freshly cut piece of foil and should have had an exposed metal
>surface at the cut edge; but your point is well taken.
You might also want to check back with the hotrod store. Many racing fuels
contain inhibitors to minimize corrosion. You are likely dealing with one
of these.
John
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John De Armond, WD4OQC | We can no more blame our loss of freedom on congress
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Mike Smith
You might also want to check back with the hotrod store. Many racing fuels
>contain inhibitors to minimize corrosion. You are likely dealing with one
>of these.
Nope. The methanol came from a 55 gallon drum of plain methanol
from the Ashland Chemical company. The lable mentioned many things,
but corrosion inhibition and racing fuel were not among them (mostly
they were warnings about not drinking the stuff and fire danger).
The owner of the speed shop assures me that it isn't doctored in any
way and that it is just commercial methanol as sold for solvent and
chemical use.
But while we're on the subject: Thanks for pointing out that corrosive
fuels issues have been solved already by the inclusion of corrosion
inhibitors. If you had stated before that it was a solved problem
then I wouldn't have bothered taking up your test! But is it possible
that the corrosion you speak of comes from NITRO fuels rather than just
plain methanol?
In a prior article you stated:
> Methanol will rapidly and completely turn light metals
> into white powder. I learned that lesson the hard way when using
> methanol as a racing fuel. If you want to see for yourself, go to
> the hardware store, buy a gallon, and chunk some aluminum foil into it.
Nowhere in this statement does it state that I have to 1) Sand the foil.
2) Heat it up. 3) Add iodine. 4) Avoid racing methanol, since it
might have an existing known fix in it (and in fact you imply strongly
that racing fuel is the problem 'the hard way when using methanol as a
racing fuel'). 5) Add water. 6) Avoid water. 7) Add salt.
At the risk of being non-scientific in my comments, I would like to
point out that I've sunk about $45 dollars into this experiment (putting
my money where John's mouth is) and still haven't seen any evidence
whatsoever that 'Methanol will rapidly and completely turn light
metals into white powder'.
Is it possible that John G. De Armond is, gasp!, wrong on a technical
issue?
> its high heat of vaporization and low vapor pressure means that unassisted
> cold starting below about 40 degrees is impossible and lots of carb
> heat is necessary at all times to prevent carb icing. I've seen
> racing carbs ice even in the summertime.
Mike Smith
away to 'fire fight' and let my last posting go without finishing
a point ...
Carb icing is most common NOT at low temperatures, like 35 degrees,
since much of the water has already left the air by then. In my
private pilots ground school classes it was repeatedly stressed that
carb icing was most common at about 60 degrees and high humidity
since then the ~30 temp drop in the carb gave you Lots Of Ice.
They also pointed out that carb ice was even possible in the summertime
depending on particular engine design ...
Looks to me like anecdotal carb ice stories don't mean much about
methanol suitablility as a fuel.
James W. Swonger
>In article <21...@rsiatl.UUCP> j...@rsiatl.UUCP (John G. De Armond) writes:
>
>
>> Methanol will rapidly and completely turn light metals
>> into white powder. I learned that lesson the hard way when using
>> methanol as a racing fuel. If you want to see for yourself, go to
>> the hardware store, buy a gallon, and chunk some aluminum foil into it.
A couple of points regarding this thread. First, "light metals" may be
something besides aluminum. I wouldn't expect aluminum to corrode without
(a) a solvent for Al2O3 and (b) an oxidizer or (c) an acid/salt plus a
galvanic couple present. My guess at a likely candidate would be
'pot metal', which I believe is some castable alloy of zinc. This junk
has a built-in galvanic couple and I would expect it to 'turn to powder'
in the presence of something nasty like a methanol/water/weak acid
solution.
Does anyone have information on what sorts of components do the t-t-p
thing and what their composition was?
Mike Smith
>In article <81...@goofy.Apple.COM> e...@Apple.COM (Mike Smith) writes:
>>In article <21...@rsiatl.UUCP> j...@rsiatl.UUCP (John G. De Armond) writes:
>>
>(Can't follow the attribution, but anyway...)
>>
>>> Methanol will rapidly and completely turn light metals
>>> into white powder. I learned that lesson the hard way when using
>>> methanol as a racing fuel. If you want to see for yourself, go to
>>> the hardware store, buy a gallon, and chunk some aluminum foil into it.
>
> A couple of points regarding this thread. First, "light metals" may be
>something besides aluminum. I wouldn't expect aluminum to corrode without
>(a) a solvent for Al2O3 and (b) an oxidizer or (c) an acid/salt plus a
>galvanic couple present.
This agrees with my organic chem text which implies that it takes
a heat and a halogen to get things cooking. I'll post the specifics
Real Soon Now. An oxidizer and a galvanic couple would help too...
>My guess at a likely candidate would be
>'pot metal', which I believe is some castable alloy of zinc. This junk
>has a built-in galvanic couple and I would expect it to 'turn to powder'
>in the presence of something nasty like a methanol/water/weak acid
>solution.
Hmmm, maybe I'll hunt up a sample or two ... I would like to see SOMETHING
happen in at least one of the metal/alcohol trials I've got running...
> Does anyone have information on what sorts of components do the t-t-p
>thing and what their composition was?
--