aluminium foil and food stored in metal cans !!

Hi,

can anyone explain to me why (as per the instructions on the box) you should not use aluminium foil to cover food stored in metal cans? I need to understand the chemical reaction, and would appreciate any help/advice or simply point me at a good book.

Regards,johnson

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Even I had this doubt...Very

Even I had this doubt...Very informative question..Thanks for all who has given suggestion...

Thanks,
Precision Engineers (http://www.mpe-ltd.co.uk/)

If the food is already in a metal can... What's the use of putting it into another?

I think it might be a precaution to galvanic corosion (putting two different types of metals in contact). Same reason they did away with aluminum wires in houses, as they shorted at the brass contact on the plug causing fires. The "more precious metal" acts as the cathode, and eats away at the anode metal. Metals corrode to easily =/ Oxides are much more stable :wink:

Usually they do except silver, gold, mercury, palladium and platinum.

http://www.engineersedge.com/galvanic_capatability.htm

http://www.corrosion-club.com/galvseries.htm

ANY dissimilar metal including precious metals. Unless your talking about oxidation, in which cause, those elements are unstable as oxides, correct

Well, gold and silver can't even be corroded by hydrochloric acid.

Ag will slowly react with HCl and Au will dissolve in a Cl atmosphere if H2O is present; vanadium and tungsten are just about as resistant to HCl as Au.

As martin pointed out, your noble metals WILL react with stuff. Nothing is completely unreactive. When I measure at elevated temperatures (200 C to 1500 C), silver can only be used up to about 700-800C (unless I'm using a reducing atmosphere). Even then, Ag has a strong tendancy to diffuse into my samples. This is one of the problems found in IC chips that are switching from Cu to Ag printed patterns. The Ag tends to diffuse all over the place wrecking the transitors etc. Ag is especially mobile when a voltage is appiled.

Most of the time I just stick to Pt wires/paste. Pt does not oxidize, diffuse, or react in any other way with my materials (and it has a predictable temperature-vs-resistivity relationship). In other words, if i were to use silver, the Ag may form some compound only a couple nanometers thick between the current collector and sample that is completely unconductive. This effectively ruins the experiment, and without alot of time and money, I would never be able to detect the layer.

I thought the same way about noble metals until i started working with them and studying them. You may not physically see a reaction, but on a microscopic level, they can be corroding, diffusing, oxidizing, and/or dissolving. The whole reason Aluminum metal does not corrode like a piece of iron, is because of an Al2O3 layer on the surface, that protects against further oxidation....and its only a few angstroms thick unless the part is "anodized" in which case the Al2O3 layer has been growth to a much greater thickness.

There are even some Aluminum alloys that "age harden" themselves. Over the course of weeks/months/years, the part will increase its strength (special applications for alloys of this nature such as aircraft rivits). You could sit there for weeks watching it, and you would never guess the sample is reacting, but it is!

There is more than meets the eye

They had even made Krypton fluoride, so what can't they make?

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