On Mon, 17 May 2004 05:29:09 GMT, "Dan White"
posted:


"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)?

I guess it might be some sort of hydrated "complex". Like most ionic
species in aqueous solution. Our understanding of "complexes" seems to
coincide, although that's possibly and artifact of the age of our
chemistry learning (me ~ 45 years

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?

That's the nub, I suspect, and why it is purportedly different from a
similar acetate "complex".

2. You have to admit that the NaCl is greatly accelerating the reaction
rate.

I can't disagree with you here, (never having tried it), but have
difficulty in explaining it to myself. I just hate salt!! It has
screwed up masses of our ag land and costs society squillions in
damage to just about everything. If it can be avoided, I will avoid
it. I once had a car at the beach where the radiator fell apart on the
outside (all the fins disappeared) while the inside was perfect.

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.

Well no, but then copper is a different kettle of fish, being on the
other side of hydrogen in the electrochemical reactivity series.
Next time my wife asks me to get rid of some rust stains, and I have
no CLR (another weak organic acid sold for the purpose of removing
lime deposits and rust stains) I will try acetic acid with NaCl and
without. Stop watch and clip board at the ready!

I think we are both
interested in the same thing, but maybe are looking at it from different
standpoints.

Or fairly similar standpoints. I see the downside of introducing salt
to rusted metal, having lived near the beach for a long time.