WG: [meteorite-list]: Preservation and storage of iron meteorites

From: Jörn Koblitz <koblitz_at_meteoritecentral.com>
Date: Fri Nov 26 06:40:30 2004
Message-ID: <E5E6112EA31FA24CB448E091C6883C0517A716_at_server2000.microfab.de>

Dear Listees,

The problem with rusting of very weathered iron meteorites isn't primarily the oxygen, but the air humidity. Rusting is an electrochemical process, which is dramatically enhanced by the presence of salts withing cracks and grain boundaries of the meteorite. The most problematic salts in this sense are chlorides like NaCl, but other salts like nitrates or sulfates will also enhance corrosion.

A) There are a number of solutions how to get rusting irons STABLE by removing or converting the incorporated salts:

1. the ULTIMATE (but most difficult and expensive!) way is to apply a hydrogen plasma to the meteorite:

In detail: you need a vacuum chamber, a gas bottle of hyrogen, tubing and gas inlet into the chamber, a vacuum pump, an exhaust to pump the hydogen out of the chamber, a microwave magnetron or rf-generator to ignite a plasma. The hydrogen plasma will reduce the iron oxides and the halogens of the salts converted to volatile components (e.g. HCl) which will be pumped off the chamber. The problem with this technique, which was first applied by Vagn Buchwald for the preservation of archological artifacts (e.g. Viking iron swords): it is almost impossible for private collectors to establish! The whole system must be explosion-proof, no presence of oxygen in the chamber, exhaust line to get the hydrogen outward your building, etc. I have done this in the past with rusty Campos and it is working perfectly. These specimens are almost as stable as freshly fallen iron meteorites. The drawback is: all iron oxides present will be converted to metallic iron (black powder)!

2. the SECOND best solution is to draw the salts out of the cracks by applying electrolysis using KOH or NaOH solution (electrochemical cleaning).
This technique is well established and described in detail here: http://nautarch.tamu.edu/class/anth605/File10a.htm#ELECTROCHEMICAL

3. a not-so-good technique is just to place the specimen in a NaOH or KOH solution, because
a) the leaching and convertion of salts in deep cracks is controlled by diffusion processes
b) it is incomplete as the halogen ions are not forced out of the cracks into the solution

B) The best methods of storing corrosion-sensitive specimens are:

1. The ULTIMATE method, but not very practical for collector who often handle their meteorite specimens, is simply to keep the specimen in concentrated KOH or NaOH solution. It will no more rust as the iron is safely passivated due to the very high pH (alkaline) value. Curious: I have seen an iron specimen (don't recall which meteorite it was) on display in a show room of the Geological Museum in Copenhagen, which was kept in such a solution (I guess, Vagn Buchwald did it!). So, if you have very valuable meteorites, this is an "ultima ratio" to preserve it (man, I should have done it with my Admire slice, 10 years ago - now its fallen apart!)

2. The second best method is to keep all humidity away from the specimen (and if you have, you can put it in nitrogen). For myself, I use a professional dry storage box, in which I place my corrosion-sensitive iron an pallasite specimens. I place commercially available desiccant (with cobalt color indicator) in the storage box which has to be changed (and dried in a microwave oven) from time to time. These measures keep the relative humidity down below 20%, which is more-or-less sufficient to prevent rusting.

3. A not so good - or even harmful - method is to apply a polymer coating on the specimens or to place it in a plastic bag, because neither will prevent the humidity (H2O molecules) from permeating through the usually few microns of polymer. The disaster is that, if corrosion has started, it is accelerated by the increasing humidity and acidity within this "micro environment". This method is only feasible, if you add desiccant to the plastic bag. However, you have to change the desiccant very often. Otherwise, it will have the same effect as without desiccant (see above).

Best regards,
J?rn Koblitz / MetBase



> -----Urspr?ngliche Nachricht-----
> Von: Jonathan Gore [mailto:jonathan301_at_earthlink.net]
> Gesendet: Freitag, 26. November 2004 06:45
> Cc: meteorite-list_at_meteoritecentral.com
> Betreff: Re: [meteorite-list] RE: Nice Dronino?
>
>
> Or storing it in oil after the alcohol/NaOH bath?
>
> JKGwilliam wrote:
> > Have any of you who are fighting with rust/decay problems
> with Dronino
> > tried storing with desiccant in an airtight container after
> treating
> > with the alcohol/NaOH bath?
> >
> > I can remember Steve Shoner telling the list about using the
> > alcohol/NaOH solution bath. As best as I can remember, he was the
> > developer of this process and had tested it over a long
> period of time.
> > Two weeks in the bath might not be enough. If the solution becomes
> > discolored, put the specimen in a fresh batch of the solution and
> > remember to stir it gently every day. Some stubborn
> meteorites might
> > take months in the solution to produce the right effects.
> >
> > Maybe Steve can enlighten us one more time on this subject.
> >
> > Best,
> >
> > JKG
> >
> > At 09:23 PM 11/25/2004, Jonathan Gore wrote:
> >
> >> I thought it wasn't a good idea to store meteorites in
> plastic bags. I
> >> would think storing it in a bell jar with the air evacuated would
> >> stabilize it.
> >>
> >> Just a thought....
> >>
> >> Jonathan
> >>
> >> Pekka Savolainen wrote:
> >>
> >>> Nope, as far as I know. This mirror-polished fellow was
> >>> stored in the air-tight plastig-bag, and some 10 months it
> >>> was a real beauty. Then it started to rust very fast, or in
> >>> fact not only to rust, perhaps "boiling" is a good word for
> >>> the process...;-
> >>> The beauty today;
> >>> http://www.dlc.fi/~nuuska/dronino.jpg
> >>> best,
> >>> pekka s
> >>> Jonathan Gore wrote:
> >>>
> >>>> Would storing it in a vacuum work?
> >>>>
> >>>> Pekka Savolainen wrote:
> >>>>
> >>>>>
> >>>>> Well, have tried everything except black magic and woodoo...;-
> >>>>> Dronino is a quite old one, accordindg Verdansky from before
> >>>>> 12:th century. Main part of the pieces was found from the very
> >>>>> wet area, so I suppose, the chlorides are not the only
> problem...,
> >>>>> the meteorite is just too old and have spent too much time in a
> >>>>> wet soil.
> >>>>>
> >>>>> http://www.geokhi.ru/~meteorit/dronino1-e.html
> >>>>>
> >>>>> As I told in my former e-mail, after all tricks my pieces stayed
> >>>>> stable some 8 - 10 months, the pieces without any methods to
> >>>>> stabilizie them couple of weeks, not much longer.
> >>>>>
> >>>>> If some happens to find to way to stabilizate this very
> interresting
> >>>>> meteorite indeed, please, let me know...
> >>>>>
> >>>>> best,
> >>>>>
> >>>>> pekka s
> >>>>>
> >>>>>
> >>>>>
> >>>>> Stephen McMann wrote:
> >>>>>
> >>>>>> Dear Pekka and List,
> >>>>>>
> >>>>>> Has anyone ever tried some of the tried and true iron
> stabilization
> >>>>>> techniques on Dronino, such as a long bath in an
> alcohol and NaOH
> >>>>>> rich
> >>>>>> solution to remove chlorides? On a related subject, I
> guess that I
> >>>>>> may not
> >>>>>> really understand the chemistry behind why some meteorites are
> >>>>>> stable, and
> >>>>>> some are not. Perhaps I will naively ask, "Is it all about
> >>>>>> chlorides?"
> >>>>>>
> >>>>>> Sincerely,
> >>>>>>
> >>>>>> Stephen McMann
> >>>>>>
> >>>>>> -----Original Message-----
> >>>>>> From: Pekka Savolainen [mailto:pekka.savolainen_at_dlc.fi] Sent:
> >>>>>> Thursday, November 25, 2004 5:33 PM
> >>>>>> To: Stephen McMann
> >>>>>> Cc: meteorite-list_at_meteoritecentral.com
> >>>>>> Subject: Re: [meteorite-list] Nice Dronino?
> >>>>>>
> >>>>>>
> >>>>>> They are not stable. The older pieces was slag in a
> few weeks or
> >>>>>> months,
> >>>>>> the new "stable" ones in 8 - 10 months. I have just
> one very thin
> >>>>>> piece not
> >>>>>> distroyed, just because it has a quite heavy lacquer. Fastest
> >>>>>> ruster I have
> >>>>>> ever seen ;-
> >>>>>>
> >>>>>> best,
> >>>>>>
> >>>>>> pekka
> >>>>>>
> >>>>>>
> >>>>>> ______________________________________________
> >>>>>> Meteorite-list mailing list
> >>>>>> Meteorite-list_at_meteoritecentral.com
> >>>>>> http://six.pairlist.net/mailman/listinfo/meteorite-list
> >>>>>>
> >>>>>>
> >>>>
> >>
> >> ______________________________________________
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> >
> >
> >
> >
> >
>
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Received on Fri 26 Nov 2004 06:40:58 AM PST