At risk of being pedantic, I want to bring out the fact that Galvanic
corrosion is not different in mechanism that "normal" corrosion, it is normal
corrosion accelerated dramatically..
Corrosion involves two chemical reactions, the cathodic, wherein the
electrons are "absorbed"... a so-called electron "sink", usually Oxygen is the
"electron sink".. and the reaction we see, the anodic reaction, where the metals
corrode, turn into salts, and donate electrons to the "electron sink".

These two reactions get in each other's way, and are slowed dramatically,
when they try to occur at the same place.. but if you can separate them, and have
them occur at separated places, as when you have dissimilar metals in
electrical contact with each other, the cathode reaction occurs on the more "noble"
surface, and the anode reaction occurs on the more active surface.  Note, this
rule does not apply when you have an alloy, like Tin/Lead, as the atoms of Tin
and Lead are too close to each other.

Do we all know that this kind of phenomenon was discovered by the Italian
scientist Galvanos, who noticed that when he plugged two different wires into a
frogs legs, and touched them together, the frogs legs jumped!   From this it is
too clear that Italian scientists must have MUCH too much time on their
hands!

Rudy Sedlak
RD Chemical Company

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