On Wed, 19 May 2004 20:27:09 GMT, "Dan White"
posted:
First of all let me say that my interest in this thread, started by Sandy,
Nope, I merely interjected my question about the need for salt into an
already existing thread. But I see what you mean.
was caused by my own questioning of why salt helped clean copper pots with
vinegar. Months ago I poured vinegar on a copper pot and it did nothing.
Then I sprinkled salt on, and the oxides just wiped away.
Wiped away with a cloth? The salt may have been acting as a scourer?
Copper is the other side of hydrogen in the electrochemical reactivity
table, so perhaps there is some difference here with iron?
I figure whatever
mechanism was working there is probably not that different from what happens
with iron.
Except for what I said above.
So on with my not-so-scientifically-controlled test:
I didn't have any rusted nails, but I did find two old 1.25 lb free weights.
These are 4" in diameter with a 1" hole for the barbell to go through. The
annular region between this hole and the outer edge of the weight was
recessed and could hold maybe a tablespoon worth of liquid, possibly more.
The annular region was embossed with the manufacturer's name and the weight.
Each weight was rusted moderately and had about the same amount of rust.
This means that there is more rust than you could casually remove, but not
so much that the weight had deep pits.
I poured vinegar into both, and then added an excess of salt to one of them.
Within hours, both were effervescing slightly. (They had bubbles collecting
on the surface). Note that this was done in contact with air, and with
plenty of surface area. After 48 hours I poured the liquid out of each into
test tube like containers. What I observe is that the vinegar/salt sample
was a light yellowish/orange color, and contained a fair amount of black
flecks and little chunks, in addition to some very small black particles.
On the other hand, the vinegar/no salt solution was a deep red color, very
different from the vinegar/salt sample. It had no flecks or chunks of black
material, but did have a fair amount of very fine, small black particles.
In both cases, black material built up on the edges of the liquid, and also
on some of the submerged surfaces.
I cleaned the weights by hand
Now this is perhaps the most important step and you have not
elaborated. How did you clean these things? The salt crystals can act
as a scourer, so if you wiped them with a rag....
and observed that the rust was gone from both,
but the vinegar/salt weight looked SLIGHTLY cleaner. I then used a brass
brush to clean them up further. After drying them out, it appears that the
vinegar/salt weight is a little brighter looking. The vinegar only weight
looks darker, as if there is dark material caught up in the fine pits and
crevices of the weight.
Could be that more of the orange rust had dissolved leaving the black
magnetite (Fe3O4), and the salt and vinegar dissolved less of this
orange rust leaving it appearing lighter. Both my examples seem
minutely more orange (lighter colour) than the non treated parts of
the nails.
Overall I'd say that there is a definite difference between the two as one
liquid was light yellow or orange, and the other was deep red. The
vinegar/salt weight also looked a little cleaner, but it is a very slight
difference. It could be that these old weights just looked a little
different from the start.
What caused the red color in one and not the other? Is the iron chloride
complex colorless, while FeCl3 is red?
I would guess that they are the same colour, containing the same
coloured ion Fe+++, but I'm not sure. I'm not even sure that this iron
chloride complex exists, as my question as to what happens to all that
excess Na+ was never answered.
My vinegar-only is definitely effervescing slightly more than the salt
and vinegar as seen this morning by swirling the bubbles away and
looking again in ten minutes for new bubbles to form.
Previously, effervescence appeared roughly similar and quite slight.
Sorry for being long-winded. Hope this spurs some ideas.
dwhite
PS. I might add clean water to each next to see if there is any difference
in corrosion rate as postulated by Sandy.
My reading suggests that the salt-treated article will rust more, even
if left dry. This is the problem, as the salt in the minute pits will
attract atmospheric moisture and act as electrolyte in minute
electrochemical cells. This will happen more in some alloys than
others.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
My experiment was with very rusted nails.
The vinegar only solution is brown(orange) and the salt and vinegar is
pale yellow. Effervescence is still going ever more strongly (though
still quite weak) at 46 hours. There seems to be more black specks
floating in the salted version. This may have been due to an original
difference in the nails. Both have a few rust particles on the bottom
of the tumblers.
The nails are imperceptibly different from when I put them in the
solutions -- slightly more yellow where the solutions have acted, but
still very heavily rusted.
I found that salt perhaps inhibits the process slightly, (except,
perhaps, as a scourer when the article is wiped with a rag?)
I worry about that salt in the rust pits, and so personally would
bever use salt on anything of mine that I valued.
My conclusion is that this procedure is useless for heavily rusted
articles. And salt makes an insignificant difference.
A wire brush and/or electrolysis might be a better way to go.
Thanks for an interesting exchange, Dan.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dan:
I have
some rusted metal soaking for about 36 hours now. I'll stop it Wed
afternoon and see what I get. I'll let you know, fwiw.
Sandy:
I'm now getting a bit of effervescence in mine. Carbonates dissolving,
I guess. That's a more promising sign, but 28 hours shows very little
cleaning. Not long ago, I stuck a very rusted hose clamp
(hydraulically applied) in vinegar in the hope that it would fall
apart. What it did do was to make the non-rusted chromed areas nice
and shiny. As there was still a lot of metal left, and not all rust as
it originally seemed, it required 3000 rpm of an 8" alumina wheel 
My impression so far is that the salt impedes the derusting process.
I have read in places that salt is added to vinegar as a mild abrasive
when rubbing a rusted item clean. This is a very different process
than the one claimed in this thread.
Sandy:
That salt and vinegar are useless for derusting rusty tools?
Pretty much, I would contend, so far.
That Charlie was being a whinging busybody by complaining about our
discussion?
Yep, see my reponse to Jim.
"Jim Wilson" wrote in message
k.net...
Sandy wrote...
Jim Wilson posted:
Hyperbole, perhaps?
Nope, comparative. Cf dropping a rock on your foot
Ok, perhaps more complex than dropping a rock on your foot, but that
doesn't say a whole lot, does it? (G)
My conclusion so far is that using vinegar to clean off rust is a
waste of bloody time
It certainly is if you watch it. (G)
In the context of whining that our discussion was OT for this
forum.
Otherwise, what was the aim of his message?
That wasn't the context. He started by disagreeing with your
assertion
that "What we need explaining is why the presence of sodium chloride
in
the vinegar is advantageous." He noted that "we" non-chemist
woodworkers
do not need that explained at all. We need only know whether it
works,
not why.
Indeed, even a correct, lucid, and perfectly presented explanation
would
be of limited utility to the majority, although it might well be
interesting to many of us. An inconclusive, jargon-filled technical
debate would have to have considerably less utility, wouldn't you
agree?
Only afterward did he observe that the thread had wandered into OT
territory, and even then he did not suggest aborting the thread, but
rather that the subject line should have been altered.
Don't get me wrong -- personally, I am quite interested in the
discussion, and have been following the thread closely, but
obviously I
do have a penchant for useless academic debate :-). I interjected
because
I felt your take on Charlie's post was wrong, and that the points he
was
really trying to make were valid, to wit: 1) most readers of this NG
neither need nor want to understand this stuff, and 2) the thread
has
drifted off topic for this NG. I still want to hear it.
Jim