Several aliminium soft drink cans (375 ml and 285 ml) which were
unopened became empty over a period of several months sitting upright
in a cupboard.  On inspection, they were still sealed and did not seem
to have any leaks.  Because they were from different companies, I
doubt it was just a bad batch with tiny holes not visibile to the
naked eye. How would this have happened?

---

Clarification of Question by jharrop-ga on 16 Jun 2006 17:36 PDT

Cans in question are all 4 cans of UDL Vodka Green Apple (4.8%
alc/vol) - they are completely empty. Shelf covered in green sludge!

The cupboard was normal room temperature. Household cleaning fluids
stored in the adjacent cupboard.

I wholly submerged one of the cans in a bucket of water. I couldn't
see any air bubbles escaping to the surface. But i've left it
submerged with a brick on top to hold it down to see whether it fills
over time...will advise results.

Prior to storing in the cupboard, the cans had been in an esky
surrounded by ice.  But they hadn't been frozen to my knowledge.

---

Clarification of Question by jharrop-ga on 18 Jun 2006 04:58 PDT

In response to brix24-ga, i put the cans in the fridge, then in the
tub of hot water.  The first can immediately showed 2 small holes.  A
second can showed a single hole immediately.  The other two cans had
to remain in the water for a minute or so before the air inside heated
sufficiently to give away a hole in each.

In some cans, the hole was on the rim; in others, in a part of the
base not in contact with the shelf.

The Red Bull cans (which were only half empty, and smaller than the
UDL cans) didn't succumb to the fridge then hot water trick.  At least
not in minute or so I submerged them.

---

Clarification of Question by jharrop-ga on 18 Jun 2006 05:00 PDT

The cans were all found to be empty within around 2 months of purchase
from Dan Murphy, which is a large liquor store which presumably turns
over its stock quickly.

---

Clarification of Question by jharrop-ga on 30 Jun 2006 21:36 PDT

Still don't have an entirely convincing answer as to how the tiny
holes came to appear in the 2 brands of can (not here, on to the
question i posted on Yahoo at the same time:
http://answers.yahoo.com/question/?qid=20060616152708AA2Absf  ).

The RedBull and UDL cans have the following in common:
- bought from the same store
- both spent a weekend in the same esky, with a bag of ice which
slowly melted, and some fruit & veg
- both were then stored on the same shelf at room temperature for a month or 2

As far as i can tell, the cans were manufactured by different companies.

We have had exactly the same thing happen. I think there were two
different modes of failure.
1. I believe that acids in the drink attack the aluminum and create
holes which allow the fluid to escape.
2. The drink freezes and bursts the pull tab cap (this is not real
obvious, you must look very closely). Then over a period of time the
fluid evaporates.

I used to work in a country pub and cans of lemonade in particular
seemed to do this a lot. The sugar or whatever seemed to eat through
the aluminium can (you can't see any holes though). A sticky floor
underneath the cartons of cans was usually the result.

You might try this: Get a pan of fairly warm water (not hot enough to
burn your hands); immerse an empty can fully in the water and look for
air escaping due to a slight pressure increase as the can and the air
inside it heat  up.

It's penetration of a potential barrier by a non-classical system. :)

Does it change your health or the taste to have aluminum rotted into your drink?

Shouldn't the aluminium oxide layer prevent this from happening?

I can taste the difference between drinks from an aluminium can and a
glass/plastic bottle. I avoid aluminium cans, I don't like the taste
and they don't have a very long shelf life.
Did the UDL cans have expiry or best before dates on them?

Re: "... UDL cans have expiry or best before dates on them?"

Best consumed before everything leaks out?
(Sorry!)

------
Regarding the temperature experiment: putting an empty can in a
refrigerator for a couple of hours should provide a little greater
pressure difference after the can is immersed in warm water.

Regarding freezing: The 4.3% alcohol should prevent freezing in ice
(but not in a freezer or some ice-salt mixtures). Freezing point of
water: 0 ºC; of 10% alcohol: -4 ºC.
http://www.engineeringtoolbox.com/ethanol-water-d_989.html

Some interesting comments on this thread:
http://ask.metafilter.com/mefi/27765

The cans of lemonade that I know leaked were still in the carton,
bought from the supermarket shelf (not fridge) and never been in the
cool room or freezer.
No idea how old they were. Not a lot a people drank lemonade.

I had some small cans, soft drinks from an aircraft bar that were left
over from an exhibition.

They resided in the back of my fridge for many years
- one day I found that a tomato juice can had done exactly the same as yours

It?s possible that the cans were somewhat defective. Something can
occasionally go wrong, and can manufacturers try to reduce the amount
of aluminum they use, so the aluminum in the cans tends towards the
thinner side.

Even though the drinks you purchased were from different beverage
producers, the cans could have been purchased from the same
manufacturer. If you?re lucky, the cans might have the name of the
manufacturer on them. I just checked two cans sold in the U.S.; one
can from a soft drink had ?REXAM? in small letters on it; another can
with beer didn?t seem to have anything that might be the name of a
manufacturer.

A Google search on REXAM showed that it is a major British can
manufacturer with multiple plants in the U.S. ? they didn?t seem to
have any plants in Australia, though they do have offices there.
?Amcor? was the name of an Australian can manufacturer, and there are
probably other manufacturers.

Aluminum is subject to corrosion in contact with alkaline solutions
and certain metal ions, but I doubt that you exposed the cans to
either of these without knowing it. Some cleaning materials are
alkaline, but then the damage would have been confined to the bottoms
of the cans if the contact were from the storage shelf.

References:

Here is a technical document where a company researched interior
defects in aluminum cans for an unknown manufacturer: (not sure if the
defects led to leaks, though)
http://www.modernmicroscopy.com/main.asp?article=66&page=2

Here is a REXAM site that has links to the steps in producing can:
(plenty of stretching and bending going on)
http://www.rexam.com/sectors/index.asp?pageid=74

Here is a site with some history of can making: (mostly of interest
here because the manufacturers have found ways to get by with less
aluminum)
http://www.cancentral.com/canc/nontext/history.htm

The following two sites just state that aluminum can corrode in the
presence of alkaline materials ? something I?d say was unlikely in
your case:
http://www.efunda.com/materials/alloys/aluminum/aluminum.cfm
http://www.corrosion-doctors.org/MatSelect/corraluminalloys.htm

Hello again, jharrop-ga,

It is possible that the pinholes formed during the time the cans spent
in the esky and they were in contact with water containing materials
that leached from the vegetables and fruit. I can?t say exactly which
materials, but I will mention some possibilities further on. But
first:

=========
The Experiment:

I was able to create small holes in aluminum foil that let the
solution it contained leak out sometime between 24 and 34 hours of
contact. I did not use a strong acid or a strong base (alkaline
material) to do this; however, at least one of the materials used was
active enough to create holes in the aluminum foil. I had previously
looked up materials were corrosive to aluminum and used a combination
of them to try to create holes in the aluminum foil. Without further
experimentation, I can?t say which material(s) was (were) responsible
for the holes; all I wanted to do was to see if something we don?t
regard as very corrosive was able to corrode its way through aluminum
in a day or two.

For a short time, photos of light shining through the holes created in
the aluminum foil are viewable at:

picasaweb.google.com/Al.holes/2006_07_03

(Double-click on any of the three photos to see an enlarged image.)

Here?s what I used: aluminum foil cupped over a small plastic
container, water, some calcium chloride pellets (used in this climate
to melt ice in winter) and some ?not-shiny? copper coins (US pennies).
I noticed that there were some bubbles on the pennies, possibly due to
air being forced out of solution, but possibly (less likely, I
thought) due to hydrogen formation. In any case, after seeing the
water still in the aluminum foil at the 24 hour point, I decided to
add a few drops of vinegar (a weak acid solution), thinking (pure
speculation) that the acid might aid in making the oxidized layer on
the copper coins more available for reduction.

That last sentence got technical, and this paragraph will be also ?
you can skip it if desired. Also, my apologies if you have a technical
background and already know this: Aluminum corrodes by losing
electrons to something else; the something else is ?reduced? in the
process. There is a phenomenon known as galvanic corrosion where
corrosion occurs when the electrons find their way to the ?something
else? using a path from the aluminum through another metal. In this
case, I was trying copper as the other metal, originally hoping that
the electrons would travel to, and be used up by, the layer of
oxidized copper on the tarnished pennies. At the same time, I also had
calcium chloride present as an independent way of corroding aluminum ?
this is obviously not the best of experimental designs (trying several
corrosion methods at the same time), but all I wanted to do is see if
I could create holes in aluminum.

Anyway, soon after adding the vinegar, more bubbles formed (suggesting
hydrogen generation, but that?s getting technical again.) I next
checked the set-up in the morning and saw that all the fluid had
leaked through the aluminum foil overnight. Holding the foil up to
light showed many fine pinholes.

End of experiment.

=========

Factors contributing to the corrosion of aluminum: 

Various web sites identify materials that can corrode aluminum; among
such materials are halides (of which table salt and calcium chloride
are examples). I decided to use calcium chloride since it is both a
halide and was also mentioned by name. Galvanic corrosion was
mentioned in some sites, so I also tried tarnished pennies as an
independent means of corroding the aluminum. The late addition of
vinegar was mostly based on speculation on my part. I would expect
vinegar by itself to have no effect; it?s a weak acid and aluminum
cans are resistant to carbonated drinks, which are fairly acid
themselves.

Stuff in fruits and vegetables:

Some fruits are acidic (relevant if the acid aided the action of
either the calcium chloride or the pennies). The fruits and vegetables
should also contain some calcium ions and some chloride ions ? but in
nowhere near the concentration that I got by using pellets of calcium
chloride. Fruits and vegetables also contain a great variety of other
substances. It is possible that one or more of these could either
accept electrons from the aluminum (that is, corrode the aluminum) or
that one or more would have a high affinity for the aluminum ions
found in the thin layer of protective aluminum oxide; this thin layer
protects the underlying aluminum metal from corrosion but dissolving
it would leave the underlying aluminum open to rapid corrosion.

(I put in copper pennies just in case the cans had sustained contact
with some metal implements.)

In summary, it is possible to dissolve holes in aluminum in a
reasonable period of time without resorting to conditions we
ordinarily regard as extreme. It is possible that there was a reaction
between something(s) from the fruit and vegetables and the aluminum;
but determining that specifically would take some work.

Web site statements on corrosion of aluminum:

?Aluminum owes its excellent corrosion resistance and its usage as one
of the primary metals of commerce to the barrier oxide film that is
bonded strongly to its surface and, that if damaged, re-forms
immediately in most environments. ?

?For aluminum, pitting corrosion is most commonly produced by halide
ions, of which chloride (Cl-) is the most frequently encountered in
service. Pitting of aluminum in halide solutions open to the air
occurs because, in the presence of oxygen, the metal is readily
polarized to its pitting potential.?

http://www.key-to-nonferrous.com/Articles/Article14.htm

----

?Aluminum develops an adherent oxide film in air which gives the metal
its corrosion resistance. Aluminum and aluminum alloys are
satisfactory materials of construction only in those services where
this film can be maintained.
?
?Aluminum is resistant to fresh, brackish or salt waters and is
employed for handling distilled water.
It is extensively used in the food industry because it is non-toxic
and does not taint food. Where they occur, aluminum corrosion
by-products are nontoxic in food and pharmaceutical products, and
nonstaining in the case of color-sensitive compounds such as nylon.
?
?Aluminum may also resist various chemicals, such as many organic
acids (acetic, citric, tartaric, malic, fatty acids).
?
?Salts of strong acids and weak bases, except salts of halogens, have
little effect.
?.
?Corrosives to avoid :
calcium chloride?

http://httd.njuct.edu.cn/MatWeb/mat-envs/aleee.htm

Technical notes: Vinegar is a dilute solution of acetic acid and
should have had no effect by itself. ?Salts of halogens? are the same
as ?halides,? of which calcium chloride is an example.

----

?Aluminum owes its corrosion resistance to the barrier oxide film that
forms immediately in a wide variety of environments. This oxide film
is self-renewing and accidental abrasion or other mechanical damage of
the surface film is rapidly repaired.

?

Chlorides are conducive to pitting and SCC, and aluminum alloys are
very susceptible to under-deposit corrosion by oxygen cell effects,
including accelerated attack under organic matter (sometimes called
"poultice corrosion").

Some other most frequent (and most avoidable) causes of damage to
aluminum structures and equipment are : galvanic corrosion and crevice
corrosion.?

http://httd.njuct.edu.cn/MatWeb/mat-cor/al___ccc.htm

?Under organic matter? is a very general term, but might include fruit
and vegetables under some circumstances.

----

Galvanic corrosion:
?Because of the position of aluminum near the top of the galvanic
series, galvanic coupling is one of the more common and needless
causes for corrosion on aluminum equipment.
Those involved in the design, fabrication, operation, and maintenance
of aluminum hardware should be aware of the corrosion potential
relationship of aluminum with dissimilar metals and within the family
of aluminum alloys.?

http://httd.njuct.edu.cn/MatWeb/mat-cor/al___bim.htm

------

Here is an Amazon site for a cookbook. If you ?search inside this
book? for ?aluminum,? you will find a few of the resulting references
mention a few vegetables that should not be cooked in (non-anodized?)
aluminum cookware because the vegetables? color will change. To me,
this suggests some small reaction with aluminum with those vegetables
at high temperatures.

http://www.amazon.com/gp/reader/0028610067/ref=sib_dp_pt/102-0934030-3993733#