[meteorite-list] Rust on iron meteorites : new method ?
From: Daniel Svensson <daniel_svensson_at_meteoritecentral.com>
Date: Sun Feb 19 10:50:59 2006
Hello Pierre-Marie and list,
I understand why you would like to use green lemon for removing rust, but
why the salt? I think your method might work better if you remove the salt
from the procedure, and add a neutralizing step after the toothbrush
cleaning. Use NaHCO3 if you think NaOH is to dangerous.
I think water is not that dangerous for meteorites as some seems to believe,
it is a very good solvent for cleaning, but make sure to dry specimen
properly afterwards. The corrosive agents in water are dissolved oxygen and
different ions. By using deionized and degased water I think it would be
safe to store a meteorite in water, especially if some amounts of NaOH are
added. This will lower the H+ concentration, which are corrosive ions.
I think it is very good to use NaOH or caustic soda solution for cleaning
for several reasons:
1) Neutralizing acids (both from nature, cleaning/etching and lemons :-)
2) Adding Na+ as a counter ion to Cl- (in order better remove present
chloride ions in meteorite / increasing the solubility of chloride salts)
3) It will kill plants, bacteria and other organisms on the surface and
inside the meteorite. Bacteria might have a big role in rusting process.
4) Removes grease, old oil etc and makes surface feel cleaner
5) Good electrolyte if you want to do electrochemical cleaning
I prefer caustic soda which is 85-100% NaOH but costs in Sweden only about 3
? for 500 g.
G?ran Axelsson: I agree in the bad nature of chloride ions in meteorites,
but I think etching with FeCl3 is not so stupid anyway. Put one meteorite in
1M HNO3 and one in 1M FeCl3 for 10 minutes and later compare the
degradation. I think HNO3 is much more corrosive and normally the time for
etching using FeCl3 is lower compared to HNO3 which makes the exponation
time shorter. The viscousity is also higher in a concentrated FeCl3 solution
which makes penetration through cracks a smaller problem.
>I sometimes de-rust objects with the following
>1. Put green lemon and salt on the rust
>2. Wait for about 30 minutes
>3. With a toothbrush, clean the object
>4. Rinse with distilled water
>I'll be making some tests on rusted Sikhote-Alin I
>have and will tell you the result. The advantage is
>there are no dangerous chemicals to use and that's
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Received on Sun 19 Feb 2006 10:50:54 AM PST