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Sandy
 
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Default Test Results was Salt and vinegar for rust removal

On Thu, 20 May 2004 09:51:42 +0800, Sandy posted:

Final report on the great Salt and Vinegar test

Before I hoik it all out and consign the tumblers to the dishwasher, I
thought I would describe conditions (About 75 hours, I think)

The salt-and-vinegar solution has just about NO colour to it; it has
NO effervescence; and a black scum on the surface. The nails are no
different from before treatment except that they have gone blacker.
There is a an amount of rust flakes on the bottom.

The "vinegar-only" still has slight effervescence occurring, and is a
strong orange/red colour. The nails are no different except a little
more rusty coloured. There is a similar amount of rust flakes on the
bottom.

As a final twist, I decanted some of the clear orange liquid from the
vinegar-only solution and added excess salt. Lo and behold, a black
precipitate occurred turning the solution almost chocolate brown and
opaque. I will leave this to settle, coz what I'm trying to see is if
this purported ferric chloride complex is less orange than the
straight ferric ion. So far, half an hour, the red colour seems to be
persisting, so unless there is a marked loss of colour, that ferric
chloride complex has not been demonstrated. Although the lack of
colour in the vinegar-salt test could be because no ferric ions have
been formed at all, just black ?magnetite?

My conclusion is that although the vinegar and the salt-and-vinegar
cause some of the loose rust to fall off the very rusty iron, the
treated surface is by no means cleaned. The appearance is not even
perceptibly changed. I can't determine if one works better than the
other, but from the colours of the solution and the rust and the
lesser effervescence, I would conclude the the salt impedes the
dissolution process.

I will rinse these nails and stick them back out in the rain and see
which ones fall apart quicker.








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