Why does sugar corrode aluminum?
Edward Zotti
the water that they can later cut into shapes using a cookie cutter. I poured
the very hot mixture into an aluminum baking pan and as I did so remembered a
warning I had heard 30 years ago as a Boy Scout--never put sugary drinks into
your aluminum canteen or you'll damage the metal. What a silly old wives' tale
THAT was, I thought. As I carried the tray to the fridge, my daughter cried
out, "Daddy, you're making Jell-O drops!" Sure enough, Jell-O was leaking out
the bottom of the tray. I took it to the sink, poured the mixture into a
stainless steel tray, then examined the aluminum pan. There were numerous pits
on the bottom and sides, one of which was an astonishing eighth-inch in
diameter. What in the hell happened? And why doesn't it ALWAYS happen? We've
had sugary frosting in that pan before, and I remember baking some sort of
apple crumble cake in it that had a ton of sugar in it. The pan discolored but
didn't pit. Is there something else about raspberry Jell-O that causes
corrosion in combination with sugar? Or am I wrong to blame sugar and it's
something else entirely? -Ed
H. Milton Peek
: Recently I was making "jigglers" for my kids--basically Jell-O with one third
IMHO it's almost certainly __n o t __ sugar, but some additive that
reacts with aluminum and aluminum oxide to produce a soluble salt. While
I don't know the composition of raspberry jello -- for sure -- I can just
guess it's analogous to dissolving other deposits in pans and glass by
using citric acid or various citrate compounds. Sorry, but my chemistry
is more than 40 yrs old, and I haven't kept up with what's in foods these
days.
Milton Peek
Jerzy Giziewicz
It is not unknown additive present in jello and raspberry flavour has
nothing to do with the corrosion of aluminum. Check the label - there is
plenty of citric acid (or somethimes tartaric acid) present in the mix.
This hot jello solution is acidic and fairly aggressive. BTW, do not use
aluminum pots for preparation any food which is acidic or requires some
viniger, citric juice, or naturally is reach in acids.
Regards ..... Jurek
Gregory Bloom
> : Is there something else about raspberry Jell-O that causes
> : corrosion in combination with sugar? Or am I wrong to blame sugar and it's
> : something else entirely? -Ed
>
> IMHO it's almost certainly __n o t __ sugar, but some additive that
> reacts with aluminum and aluminum oxide to produce a soluble salt. While
> I don't know the composition of raspberry jello -- for sure -- I can just
> guess it's analogous to dissolving other deposits in pans and glass by
> using citric acid or various citrate compounds.
Aluminum is an extremely powerful reducing agent. Indeed, if it were not
for the way the hexagonal crystalline structure of Aluminum Oxide neatly covers
the surface of Aluminum with a protective coating, Aluminum would spontaneously
burst into flames on exposure to the Oxygen in the air. It is this nifty oxide
coating, by the way, that makes aluminum wire so dangerous - the points of
contact can become oxidized to the point where the resistance increases and
it gets hot. This is why Al wiring was banned. Anyhow, the reason your Jello
pan dissolved wasn't the sugar, but some oxidizing ingredient such as acid.
If you're of an experimental bent, drop some Al foil in sugar water and some
in vinegar (or orange juice, or the ever-popular Ketchup) and see what happens.
Gregory Bloom g...@evolving.com (303)689-1226(vox) (303)689-1399(fax)
Evolving Systems, 8000 East Maplewood Avenue, Englewood, CO 80111 (rox)
Jack Treger
GB>contact can become oxidized to the point where the resistance increases and
GB>it gets hot. This is why Al wiring was banned. Anyhow, the reason your Jel
GB>pan dissolved wasn't the sugar, but some oxidizing ingredient such as acid.
GB>If you're of an experimental bent, drop some Al foil in sugar water and some
GB>in vinegar (or orange juice, or the ever-popular Ketchup) and see what
GB>happens.
That's also why it is suggested not to use Al pans to cook tomato
sauces or other acidic foods, in order to avoid solubilizing and
ingesting Al. Though, I don't know if the medical community has
definitively linked Al ingestion to any disease.
---
* SLMR 2.1a * ##################################
H. Milton Peek
That sugar doesn't corrode aluminum seems to be evident every day from
the fact that soft drinks -- many of which have high sugar concentrations
-- are "bottled" in aluminum cans.
Milton Peek
John D. Sutter
>
>That sugar doesn't corrode aluminum seems to be evident every day from
>the fact that soft drinks -- many of which have high sugar concentrations
>-- are "bottled" in aluminum cans.
> Milton Peek
>
The cans might be aluminum but they're coated with a thin layer of
some polymer internally. The acids in soft drinks would make pretty
short work of the cans otherwise..
-- John
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Barbara O'Keeffe
: -- John
Especially if you remember that both Coke and Pepsi have pHs of about 2.5!
--
*** Barbara O'Keeffe email: boke...@nova.gmi.edu
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in soft drinks bottled in aluminum cans? It's easy enough to have a water-
resistant polymer coating the inside, but how often is the coating process
incomplete?
Sugars, and in fact any glycol, will corrode aluminum. Aluminum hydroxide
Al(OH)3 is sparingly soluble in water, because the Lewis acid Al(3+) will
coordinate to an OH attached to another aluminum, so that you get in effect
an insoluble polymer. Aluminum metal is sufficiently electropositive that it
"ought" to react with H2O to give hydrogen gas. It doesn't do this because,
just like magnesium metal, it gets coated with a very thin layer of insoluble
hydroxide or oxide. Now any reaction which forms a ring involves less loss of
entropy and so is favored (assuming no ring strain, of course). This is why
adding 2 HOCH2CH2OH to a weakly acidic solution of B(OH)3 in H2O produces a
rise in acidity ---> (-OCH2CH2O-)2B(-) H3O(+) Sugars, which have also -OH
groups on neighboring carbons, can do this too .The reaction with Al(3+) is
less favorable, I think, than with boron, but is still effective enough to remo
ve the protective oxide/hydroxide layer .
Tyronaut
>That sugar doesn't corrode aluminum seems to be evident every day from
>the fact that soft drinks -- many of which have high sugar concentrations
>-- are "bottled" in aluminum cans.
> Milton Peek
That is correct, but if you break a can so that you can see (and touch) the
inside surface, you'll notice that it's got a polymer coating.
Victor
Akira Kawasaki
writes:
(snip)
> That's also why it is suggested not to use Al pans to cook tomato
> sauces or other acidic foods, in order to avoid solubilizing and
> ingesting Al. Though, I don't know if the medical community has
> definitively linked Al ingestion to any disease.
>
There seems to be a growing suspicion that Altzheimer's Disease (did I
remember to spell it right?) is connected to a build up of aluminum in
the brain. AK
greg franks
<g...@evolving.com> wrote:
>It is this nifty oxide
> coating, by the way, that makes aluminum wire so dangerous - the points of
> contact can become oxidized to the point where the resistance increases and
> it gets hot. This is why Al wiring was banned.
i do not understand what you just said. as resistance increases, the
current decreases so it is not going to get hotter.
thermal runaway is when so much current is going thru a resistor than
it heats up. as it heats up, the resistance decreases which makes the
current higher which makes it get heater which makes it descrease in
resistance... until it is red hot and burns in two.
i thought that Al wiring was banned because over years the Al
lost its shape where the connectors were screwed down on and
caused arching.
--
greg....@msfc.nasa.gov standard disclaimers
DON'T BLAME ME, I VOTED FOR THE "OLD ELVIS" STAMP!
Thomas S. Zemanian
greg....@msfc.nasa.gov (greg franks) wrote:
> In article <3glj8s$j...@citadel.evolving.com>, Gregory Bloom
> <g...@evolving.com> wrote:
>
> >It is this nifty oxide
> > coating, by the way, that makes aluminum wire so dangerous - the points of
> > contact can become oxidized to the point where the resistance increases and
> > it gets hot. This is why Al wiring was banned.
>
> i do not understand what you just said. as resistance increases, the
> current decreases so it is not going to get hotter.
> thermal runaway is when so much current is going thru a resistor than
> it heats up. as it heats up, the resistance decreases which makes the
> current higher which makes it get heater which makes it descrease in
> resistance... until it is red hot and burns in two.
>
> i thought that Al wiring was banned because over years the Al
> lost its shape where the connectors were screwed down on and
> caused arching.
>
I don't know the reasons for banning Al wire, but Greg Bloom is correct.
Although the increase in resistance causes a decrease in current, one must
also bear in mind that there is a load reactance in series with the
contact. As the resistance of the contact is increased, more of the
voltage drop takes place across the contact. Think of a resistive voltage
divider, and imagine what happens as you change one of the resistances.
--Tom
--
The opinions expressed herein are mine and mine alone. Keep your filthy
hands off 'em!
Tony Buckland
>i do not understand what you just said. as resistance increases, the
>current decreases so it is not going to get hotter.
No: power = current * the _square_ of the resistance. And that
power will be dissipated mostly as heat.
Tony Buckland
><g...@evolving.com> wrote:
|>It is this nifty oxide
|> coating, by the way, that makes aluminum wire so dangerous - the points of
|> contact can become oxidized to the point where the resistance increases and
|> it gets hot. This is why Al wiring was banned.
The way I heard it, the problem was aluminum wire breaking under
the normal stresses involved in installation and repair. Copper
can be bent many more times before it fractures enough to create
a hot spot.