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Re: Removing Rust [oxalic acid??]

Hi Steven, hi list,

[Steven R. Schoner wrote:]

>The real problem with rusting in meteorites is chlorine.  Rinsing the
>meteorite with water, (tap water) should never be done if any
>of these treatments is used.  For some reason, meteorite irons have
>an affinity for chlorine, and it is chlorine that is the main cause
>of rusting.

[snip]

Steven, thanks for the very useful discussion of the role of chlorine in
promoting rust, and the formula and procedure for removing the villainous
chlorides.

A couple of months ago, during a discussion of rusting problems, someone
recommended boiling (!) irons in de-ionized de-mineralized water, changing
the water several times, and then drying throughly. At first I was
sceptical, but then it occurred to me that this somewhat odd procedure was
probably intended to flush out chlorides, which as you explain are the main
culprits. Both iron chloride and nickel chloride are highly soluble in
water, so this strategy should work just fine, as long as the specimen is
dried carefully afterwards by a soak in alcohol and a stay in a warm oven.
I haven't tried this myself yet.

I have, however, wondered whether there was some better way -- using a
chemical which would react with the chlorides, rather than just trying to
dissolve them and flush them away. This would work better in specimens
which had hairline fractures, for example, as only a tiny amount of
solution would be needed to react with the chlorides, compared to how much
would be needed to dissolve them and flush them away.

It looks like you have hit the nail on the head -- using sodium hydroxide
to react iron and nickel chlorides to sodium chloride. Not that sodium
chloride (common salt) is such a blessing (we all know what sea water does
to iron) but at least it is much less hygroscopic than the chlorides of
iron and nickel -- it has much less tendency to absorb water from the
environment; as long as the specimen stays dry, a little bit of dry salt is
not a real hazard. Of course, it would be a good idea to rinse the specimen
in distilled water after its sodium hydroxide treatment, to get rid of as
much sodium chloride as possible.

Now I want to throw out a question about rust removal. After adding a very
rusty Toluca to my collection recently, I did an Internet search for "rust
removal" and came up with lots of hits for "Naval Jelly" and "oxalic acid".
I wondered which was better, and whether either would remove rust without
affecting the unoxided iron and nickel. Today I stumbled onto a thorough
discussion of removing rust from antiques at:

http://www.gold-kiser.com/project2+.htm

Well worth taking a look at. Look especially at the comments on Naval Jelly
and oxalic acid. It turns out that Naval Jelly (a trademark of Loctite) is
phosphoric acid, and judging from Dan's experiences with Ospho, could best
be avoided. Darryl also indicates that Naval Jelly definitely DOES attack
the iron. The antiques restorer comments negatively on Naval Jelly's
aggressive properties, and recommends oxalic acid instead, going into some
detail about how to use it. I have the impression that it has little if any
effect on the base metal. Does anyone with a chemistry background have a
professional opinion about this? Or about what effect oxalic acid would
have on common inclusions (sulphides, phosphides, graphite)? What would it
do to the oxide fusion crust (magnetite?) of a fall that was recent enough
that the crust was only slightly rusted? (Not an issue with my Toluca --
fusion crust was already past tense long ago!)

Am I maybe better off just to go after it with a wire brush, followed by a
chloride neutralizing soak?

Best wishes to all from sunny (at last!) Amsterdam,

Piper R.W. Hollier


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