[NewCandle] Measuring Half-Cell Charge

[Frederick Sparber]

Some added info.

http://www.terrific-scientific.co.uk/Topics/Corrosion/Explain/Corrosion-6.htm

"However, other metals do not oxidise in this way. For example, you
may think that aluminium does not corrode, as we see unprotected
aluminium windows and equipment all around us - and it does not
corrode away like iron and steel.
As we saw in experiment 2(1) - aluminium foil in water will not
corrode, but when salt is in the water the aluminium foil corrodes
rapidly. Why?"

"The answer lies in the way that Aluminium corrodes. Aluminium
corrodes very quickly (actually much more quickly than Iron and
Steel). However, the oxide that forms when aluminium atoms oxidise
does not fall off like the rust on iron, but clings tightly to the
surface of the aluminium. Very quickly, a hard layer of aluminium
oxide covers the metal, and protects the aluminium metal beneath. No
more aluminium can oxidise, as it has been sealed off from the oxygen
and water needed to make the reaction happen.
When salt is added to the water, the powerful Cl- ions attack the
aluminium oxide coating, tearing it from the surface and exposing new
aluminium metal. As soon as this aluminium metal corrodes into
aluminium oxide, it too is stripped from the surface by the Cl- ions.
The natural protection that aluminium gets from its oxide coating is
lost. This is the reason that aluminium cars and equipment will often
corrode badly if they are used in or near the sea.

Copper metal also corrodes in this way, but forms a bright green
coating of oxide which protects the copper from further corrosion.
This is why the Statue of Libery in New York is still looking as good
as the day it was erected in 1886. Had it been made out of Iron it
would have rusted away by now (For example the iron and steel Eiffel
Tower in Paris, erected in 1889, has undergone major replacement and
restoration work to remain standing)."



On 9/8/07, Frederick Sparber <fsparber at gmail.com> wrote:
> Hi Keith, you wrote:
>
> " I would suggest a stainless steel pipe rather than the copper float;
> if you are using coarse carbon there is no need to pack it with
> a ram, but you do need good electrical contact with the pipe
> and copper oxide is poor in that regard. Some kind of
> pressure on the carbon stack will greatly reduce the ohmic
> resistance and improve the circuit also. It might be hard
> to pack the copper float properly because of the shape."
>
> K.
>
> I'm well stocked on vinergar and salt and a copper float, but no
> stainless steel.
>
> If only I could stuff a balloon into the float and inflate it.  :-)
>
> http://www.chem.umn.edu/outreach/Card-SaltVinCopper.html
>
> Fred
>