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

[Ingo Herkstroeter]

Hi Göran!

Thanks for this very interesting informations!

Ingo

 --- Ursprüngliche Nachricht ---
> Von: Göran Axelsson <axelsson at acc.umu.se>
> An: meteorite-list at meteoritecentral.com
> Betreff: Re: [meteorite-list] Rust on iron meteorites : new method ?
> Datum: Sat, 18 Feb 2006 20:13:39 +0100
> 
> 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
> >
> >
> >  
> >
> 
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