[meteorite-list] Rust on iron meteorites : new method ?

[Göran Axelsson]

Hello list,

I'm writing this as a collective answer to this thread and some other 
earlier threads and contains one half replies, one half ideas and one 
half ramblings.... I'm a physicist, not a mathematician.

I'm always surprised whenever a new recip for protecting meteorites from 
rust appears and it contains chlorine ions. Why do you propose to use 
salt? That is usually a short road to rust in cars just as in meteorites 
(lawrencite).

The NaOH method has nothing to do with neutralising acids. It is a way 
to heightening the PH value in the solution and to passivate the surface 
of the iron to prevent rusting. Usually Iron resists rusting very good 
at higher PH values.

Chloride ions works as a catalyst for the reaction of turning iron, 
water and oxygen into iron hydroxides and oxides and isn't consumed in 
the process. If you remove the chlorine ions then you have slowed down 
the process a great deal and if you remove water then it will move at a 
geological timescale.

If you only remove the water then it will also be a very slow process as 
the chlorine ions is locked up as a salt whenever it dries up.

But ferrous chloride (I've heard about people using it to etch 
meteorites, sounds stupid to me) as a salt is very attracted to water. 
In an atmosphere with just a bit higher humidity it will start absorbing 
water and soon you have a drop of rusty water instead of a grain of 
ferrous chloride. This is what I guess the drops of red water on Marcin 
Cimalas Nantan contains together with iron hydroxides.

The only method that I really believe in for meteorite protection in the 
long run is to remove the chlorine. By lookin on a similar area where 
chlorine ions is a big problem we can learn a trick or two.
Archeologists are recovering iron artefacts that have been lying in salt 
water for hundreds of years without any major damage. This is the case 
if there is no oxygen present, but once recovered the rusting process 
starts.
The way marine archeological finds are treated sounds to me the right 
way to go. Basically they use electrolytical treatment to drive the 
chlorine ions out of fractures in the metal. The bath is a waterbath in 
deionised water with NaOH added. This water is changed a number of times 
and the levels of chlorine ions are measured. In the beginning it isn't 
important to use deionised water but in the end it affects the end result.
A complete treatment usually takes from a month to half a year and 
longer for bigger artifacts.

A simpler method used is sometimes just to do the same process but 
without any electricity. This works on the principle that all ions moves 
randomly in a liquid so eventually most chloride ions will end up in the 
liquid. Without the electricity to push the ions in the right direction 
this will take a much longer time.
This method is the one that I think sounds most like the alcohole and 
NaOH method used on meteorites.

I have a really rusty Nantan that I plan to test the electrolytical 
method on but I haven't started yet.

As a side note, I've heard about silica gel used for keeping the air dry 
inside cabinets. This is a good idea but with a warning. The silica gel 
consists of a mineral called zeolite, it's the mineral worlds sponge and 
absorbs water inside holes in the crystal structure. The water is not 
chemically bound to the zeolite which means that if any part of it 
touches a meteorite, the water is free to use for chemical reactions (rust).

Well, as I promised, not so much coherence, more or less free ramblings. 
Please, correct me if I'm wrong as this is a discussion list. 
Disclaimer, I'm no chemist, I'm a physicist.

And in the end, I don't want to eat in a bakery where they use NaOH, 
then it is no more Buckleboo, only boo hoo...

  ;-)

Regards, Göran

Pelé Pierre-Marie wrote:

>Hello,
>
>I sometimes de-rust objects with the following
>solution :
>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
>5. Dry
>
>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
>pretty fast.
>
>Best regards,
>
>Pierre-Marie PELE
>www.meteor-center.com
>
>
>  
>