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h12721
10-10-2007, 10:03 PM
This is big “Off Topic” but metal is involved.
The Moderators may remove if not suited.
To all the Chemist and Scientist.
I did bake an apple cake. Made yeast dough and used apple slices on top. All went well and after it cooled down I covered the whole cake with aluminum foil. The one the girls have in the Kitchen on a Roll. I covered just the top, not air tight.
Now comes the good part. After three days the aluminum foil was full of Pin Holes. Just there where it lay on the apples slices, How come?
Any explanation?
Hilmar

dp
10-10-2007, 10:06 PM
Bi-metalic corrosion. The pie serves as an electrolyte and the pie tin and the aluminum foil act as a short-circuited battery. The foil gives up it's molecules in the process. Doesn't sound very healthy.

Al Messer
10-10-2007, 10:18 PM
Apples are acidic. They will turn a shiny Carbon Steel knife blade a lovely shade of Blue/Black if it is not thoroughly washed after paring an Apple.

Fasttrack
10-10-2007, 11:24 PM
Yeah it doesn't even need the pie tin as the cathode. An oxidation reducion reaction can happen with the acid. Basically the aluminum is oxidized and the hydrogen is reduced and you form hydrogen gas and corroded aluminum.


<edit> someone should have caught me sooner - i mixed up the cathode and annode!

tattoomike68
10-11-2007, 12:11 AM
Go to McDonalds, get a coke, drop a penny in and see it in about 4 days if you can find a speck of it at all.

You can chemical mill with coca cola, I kid you not.

Paul Alciatore
10-11-2007, 12:13 AM
Yes, Coke makes a good battery acid. And we drink it.

oldtiffie
10-11-2007, 12:22 AM
Yes, Coke makes a good battery acid. And we drink it.

And you can clean "pennies" with it and even use it as soldering flux!!!

tattoomike68
10-11-2007, 12:28 AM
Yes, Coke makes a good battery acid. And we drink it.

No more rum and coke for me its tequila sunrises from now on.

Fasttrack
10-11-2007, 01:20 AM
aww cokes good for you - cleans your insides, shines 'em right up!

Weston Bye
10-11-2007, 06:15 AM
I remember a line from a TV commercial (advert) from my distant childhood: "Mary's stomach acid burned a hole in this handkerchief."

Hydrochloric acid - something that we are advised to wash off immediately if we get it on our skin.

Benesesso
10-11-2007, 06:59 AM
>"The one the girls have in the Kitchen on a Roll. I covered just the top, not air tight.
Now comes the good part. After three days the aluminum foil was full of Pin Holes. Just there where it lay on the apples slices, How come?
Any explanation?
Hilmar"<

Hmmm, this calls for an investigation!

First, why did the pie last 3 days? Didn't it taste good? Are you a good cook?

Second, I think the girl you rolled in the kitchen used a toothpick to punch the holes. Did you leave her unsatisfied, frustrated and horny?

Third, apples contain malic acid. This is a weak acid and only slightly corrosive to aluminum, but it could be the culprit if the girl didn't do it.

Fourth, corrosion occurs at anode sites, so a steel/tin pie pan would be the cathode---if it were involved.

Any pictures of the pie, foil, and of course, the girl?

andy_b
10-11-2007, 09:25 AM
your cake ate into the aluminum the same way tomatoes do (that's one reason not to use aluminum pots to cook tomato sauce or cover leftovers with aluminum foil if they have tomatoes in them). as others mentioned, it is not the healthiest thing to have your food contaminated by aluminum, it is suspected as one of the contributing factors in Alzheimer's. about the only thing my wife and i use aluminum foil for these days is to line the bottom of the oven.

andy b.

Fasttrack
10-11-2007, 12:03 PM
Incidently, the standard reduction potential for aluminum at room temperature in an acidic solution (i.e. where the cathode is the hydronium ion) is -1.66 volts. I would consider that to be fairly corrosive. The reason it doesnt get eaten up right away is because the acidic solution is so dilute ... and i suspect that the aluminum foil isn't pure aluminum ...

stuntrunt
10-11-2007, 02:33 PM
Was the cake sweeter on the third day? If it was, thanks for the good tip...
Theres no better taste than that of a cigarette you handrolled after working copper or silver...Wel maybe the taste of a wine or port that sat in a crystal decanter for some time ;)

Alistair Hosie
10-11-2007, 02:44 PM
Yes John Stevenson drinks battery acid all the time hence the unblemished complexion. He used to be a model you know !!!! He was in two famous tv adverts one for hemorrhoid cream and one for S A S balaclava's .:D Alistair

oldtiffie
10-11-2007, 03:58 PM
Deleted by author.

h12721
10-11-2007, 10:28 PM
OK guys,
I just disconnected my self from The Power Company.
Cake plate on bottom apple cake in the middle Aluminum Foil on top>
Bingo, instant 1.66 Volt battery. So 1.66 X100= 166 Volt .Now I have to buy a DC motor for my lathe. But wait, every three days I have to bake 100 cakes. Na forget it. Then there will be no time for the lathe.

But Thanks for the replays and answers.
Hilmar

Fasttrack
10-11-2007, 10:43 PM
Well before someone else jumps in to correct me, -1.66 volts is the standard reduction potential between hydrogen ions in solution and aluminum atoms. So the actual voltage produced at a given temperature and a certain concentration is given by the nernst equation, but you also have to include a time variable with the concentrations, since they change as you use up the h+ ions. So you'd need even more than 100 ... :D

Benesesso
10-11-2007, 11:16 PM
Corrosion rates can be measured by current but not voltage. E merely indicates the potential for corrosion. Alum. can survive fairly well in nitric acid, but HCL and NaOH will readily disolve it.

Fasttrack
10-12-2007, 12:26 AM
Right - but as the ox-redox reaction continues the voltages change as the concentrations change.


The reason it doesn't disolve in nitric acid is because nitric acid is an oxidizer as well - so the aluminum forms a pretty thick aluminum oxide coating that protects it from further attack.

Your Old Dog
10-12-2007, 06:29 AM
Have you thought about "BAM", as in punching it up a little and using stainless steel heat treating wrap?