Corrosion of metal in methanol, the last test report ...
Mike Smith
At that time there was a flame fest going on over the tendency
of alcohol, specifically methanol, to corrode metals. Some
asserted that you could toss a chunk of aluminum foil into some
methanol and it would rapidly be consumed. Others asserted that
that there was little problem from corrosion (I was in this group).
I conducted an experiment for a few months to see who was right.
The short term (couple of months answer) was that both sides had
some truth and some hyperbole. Metals corroded, but less than
they did in plain water, for the metals tested. I also cited some
references that tended to support that conclusion.
After a few months, I stopped posting about it, since little had
changed; but promised a follow-up if anything significant showed up.
Time passes, and attention wanders... the rack of test tubes gathers
dust in the back corner of my desk (behind the monitor, under the
duck pictures ...). Well, the day comes when it's time to clean
up the desk and toss out the trash. I find the test rack again ...
This will be my last posting on this particular experiment since
I will be cleaning up the apparatus and tossing out the leftovers.
What has a year shown? Not much more than 2 months did. The general
conclusion still stands. The distilled water controls corroded more
than the methanol samples. The acidified 80% methanol/ 20% water/ 1%
acetic acid samples were next. The 80% methanol/ 20% water followed,
and the least corrosive were the straight methanol test samples.
Yes, methanol will corrode metals. Yes, methanol is less corrosive
than plain water, and to some extent acts as a protectant when mixed
with water. No, methanol is not The Great Metal Destroyer.
The final data: (all samples dated 5/90)
Some samples dried out. I guess that some rubber corks were
not seated well enough for 1 year of neglect ... If this is
ever tried again, I'd recommend a check every so often ...
(I could of sworn I'd checked them just a quarter ago :-)
Aluminum foil
methanol
Slight surface corrosion with some pitting. One hole
of about pinhead size at a corner/crease.
MeOH/H2O
Dried out. Left a white powery dust on the surface of
a uniformly corroded thined out sample. (The sample
is fragile now, and very thin.)
Zinc
methanol
Bright shiny sample. No visible evidence of corrosion.
The liquid is a light golden yellow color. Kind of like
medium light pee.
MeOH/H2O
Sample is intact, with a light powdery white deposit on
the bottom of the test tube and some light white deposit
on the sample. There are some occasional 'cancers' of
white deposit on the surface of the sample. Like white
powdery zits... Liquid is clear, i.e. no color.
MeOH/H2O/acetic acid
About 1/3 of the liquid evaporated. Liquid is clear.
The sample looks almost exactly like the MeOH/H2O sample,
but with heavier deposits on it and on the test tube.
Distilled water
A little worse than the acidified methanol water mix.
The liquid is a milkey white. The deposits are a bit
more powdery and look about the same or maybe slightly
more copious. Overall, not significantly different from
acidified sample.
Iron nail
methanol
Sample dried out. Slight redish deposit on the bottom
of the test tube. The nail has a few rust spots on it.
Looks about like a nail that has been left in a wet place
for a little while (2 days?) and just started to rust a
little.
Brass plated iron picture hanger hook
methanol
Sample dried out. Slight deposit on the bottom of the
test tube. Sample looks, overall, in great shape.
This could be due to drying out, but there is only one
small rust spot on the sample.
MeOH/H2O
About 3/4 of the liquid evaporated, but the sample is
still covered by liquid. There is an about 3/16 inch
flocculent red deposit on the bottom of the test tube.
Sample has a couple of small sized red rust flowers on
the surface. Liquid is clear.
MeOH/H2O/acetic acid
There is about 1/2 inch of dark red/brown varigated
flocculent deposit on the bottom of the test tube.
The brass plate is visibly peeling from the sample.
The upper two inches of the liquid covered area of
the test tube has an opaque deposit of 'dried blood'
colored stuff. The rubber cork has a mushroomed end
where something has made is swell. No other sample
has any change in the rubber cork. The surface of
the sample that has no plating has a very rusty look.
Something unusual happend in this sample ...
Distilled water
There is a dense 1/4 inch deposit of squash yellow
powder on the bottom of the test tube. The liquid
is a cloudy yellow. The sample has significant spots
of black/rusty areas. This sample is in between the
the MeOH/H2O sample and the acidified sample.
Carburetor chunk
MeOH/H2O
Liquid is clear and clean. There is a very slight
deposit of white specks on the bottom of the test
tube. There are a few (3 or 4) dusty white patches
on the surface, but they don't show up any more on
the broken edge than on the finished surface. Seems
like they have formed on spots that may have a small
contaminant on/in the sample? This stuff has very
little reaction to the liquid.
Conclusions:
Electrolytic couples in an acidified methanol/water solution
seem to be real loosers. Water is almost as bad, though I
didn't test acidified water vs. acidified MeOH.
Water is far worse than pure methanol with the metals tested.
Keep water out of your methanol fuel if at all possible ...
Keep acid contaminants out of your methanol fuel.
A test should be done with the methanol changed every day
for a year (rather than just letting it sit for a year) since
there is undoubtedly some effect on the reaction from having
the reaction products accumulate in the liquid.
If you can plumb water without getting corrosion, then you
can plumb methanol. It's different than plumbing for water
or for gasoline, but it isn't an earth shattering problem...
The chunk of carburetor I used was one of the more resistant
samples tested, but if it was in a carburetor with other
metal fittings making an electrolytic couple, who knows...
Well, there you have it. The almost conclusive almost scientific
test of the corrosive effects of methanol on typical metals.
So who's going to make the first plastic/nylon carburetor? And
what about fuel injectors?...
--
E. Michael Smith e...@apple.COM
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