wrote in message
...
On Thu, 27 Oct 2011 07:51:16 -0400, "Jim Wilkins"
wrote:
....

I read both several times. Interesting. I can sort of see the pitting
type of corrosion more than the crevice type. I am not sure that it is
the whole explanation. Some of the considerations that puzzle me a

1) Why would a weak local battery not be swamped by a 2.5A current
passing through the whole system?
2) Why are the pits, if they develop as described in the article, so
deep and apparently so uniform in shape (I enlarged the photo - most
of them seem comma shaped)?
3) Why does one not see similar phenomenon with brass? There I am
removing copper from zinc. One would have thought that local batteries
would if anything be "stronger".

There are other considerations derived from the previous experience of
similar pits developing under a resist. However, I am not even sure
this is the same phenomenon. The pits sure look similar.

I am going to run a few test and see what gives.

Michael Koblic,
Campbell River, BC

The undergrad chemistry courses skimmed lightly over a very wide field of
industrial applications. They told us we weren't really chemists yet, but
when (if) we got a job in industry we knew enough theory to understand the
explanations, many of which were proprietary trade secrets. Electrochemistry
is particularly secretive about the details that make one battery better
than another. It's still black art, or FM as we say in electronics.

I did check other references. Do you really want to dive into the theory of
redox potential?

jsw