"Sandy" wrote in message
...
On Mon, 17 May 2004 04:44:41 GMT, "Dan White"
posted:


"Unknown" wrote in message
.. .
On Fri, 14 May 2004 16:30:02 GMT, "Dan White"
wrote:

,;
,;"Charles Erskine" wrote in message
e.com...
,; More than you probably wanted to know:
,;
,; http://yarchive.net/metal/rust_remove.html
,;
,; snip
,;
,;This is the post I pasted in this thread originally to try and
answer
the
,;original question.

OK I missed your original post. I wrote the article you refer to. I am
a chemist and do know what is happening in this procedure so let's
start fresh.

What is it that needs more clarification on this topic? You ask the
questions and I will try to give a reasonable explanation.

I had a feeling you were the same person as the original post I pasted.
Sandy had the original question and I was trying to help. The only thing
I
still don't understand is exactly what the "complex" is that drives the
Fe203 to dissociate and reform this complex with Cl-. Is it some kind of
hydrated Fe complexed with Cl-?

thanks,
dwhite


Thanks Dan, that's my question exactly.
I can't see the difference between a ferric chloride complex and a
ferric acetate complex. The thing that drives the reaction in my
understanding is 6H+ + Fe2O3 -- 2Fe+++ + 3H2O
That formation of water is what moves the reaction to the right.
For me, salt is just going to cause problems down the line when it
sets up corrosion cells in the fine interstices of the previous rust
pitting. Unless someone can show that it is invaluable in the
derusting process with weak acids, I would advise to stay well away
from it. As I said, I far prefer mechanical derusting with a non-polar
solvent (kerosene or CRC) for anything valuable. YMMV

Just 2 comments:

1. It may just be that my chemistry was so long ago, but I'm not sure of the
usage of the term "complex" in this context. Are we calling an FeCl3
molecule a complex (I didn't think so)? My recollection is that a complex
had more to do with Van der Walls forces attracting surrounding molecules
such as the solvent to the ion or molecule in question, as if it were
chelated or sequestered. What is the complex that results from the
rust-chloride reaction?

2. You have to admit that the NaCl is greatly accelerating the reaction
rate. Just do like I mentioned and sprinkle salt on a copper pan wetted
with vinegar. You will see the fastest reaction where the salt is. It
seems you are looking at this from the standpoint that salt does nothing,
and are challenging someone to prove otherwise. I think we are both
interested in the same thing, but maybe are looking at it from different
standpoints.

regards,
dwhite