[meteorite-list] Re: Etching Compounds (Double Standard)

From: MexicoDoug_at_aol.com <MexicoDoug_at_meteoritecentral.com>
Date: Mon Sep 13 12:55:02 2004
Message-ID: <11FF090D.46F265AA.0BFED528_at_aol.com>

Hola Veiocity,

I just wanted to comment on the etching project you have gotten into. I haven't looked at the chemistry going on with the Ferric chloride solution you bought, and hopefully will do that if for no other reason than to walk through what other side reactions are going on for my own benefit. My iron chemistry is somewhat "rusty" :)

So while I may still need to get enlightened a bit on the subject, I wanted to raise the following issues:

Commercial FeCl3 solution is probably saturated at w/w about 50% water in approx. 0.1 molar HCl (hydrochloric acid). I think the solution you are buying is such an acidified saturated solution.

So, for all the pain being taken in the concentrated HNO3 (nitric acid) process and nearly pure ethanol, it would seem we are dealing with a major league double standard when comparing the two etching procedures, since the FeCl3 is simply an acidified aqueous solution.

And depending on who you buy it from - whether they use distilled water and "clean" HCl when made in bulk, "cheap", is worth checking what you get for your money. I don't know what other nasty ions could be floating in there. A true comparison would be to compare with buying FeCl3 crystals (very very hydroscopic if memory serves), reagent grade HCl, your own distilled water and the same good straight grain alcohol. Not the premixed Margarita at Radio Shaq.

Now, whether it works initially is not at issue FeCl3 etching solution straight from the bottle should work fine, without heating it and here at 28 centigrade is happens in one minute. Then you have your pure grain alcohol ready and rinse it in several baths and then soak it for an hour or so and rinse a couple of times again.

My suspicion is that the 1 molar solution of nitric acid in distilled water you suggested from the start might be just as "good". If you follow the alcohol rinsing procedures, and perhaps better, if it is reagent grade instead of from the big vat of low grade PC board etching solution. And the nitric doesn't seem to darken the metal as much as the FeCl3, so there personal preference comes into play.

No one has yet to come out and say the FeCl3 process doesn't work, BUT: many people complain about rusting etched slices and then sometimes just leave it at chance or the specimen itself. This in the case of both HNO3 and FeCl3 methods. Then people have been heard saying - I have had no problem with FeCl3 etching and it is five years later now.

So whether you have problems or not probably will depend on all of the above concerns plus a little luck on you specimen composition and history. If you are having fun etching the large TKW commercial irons, you probably can enjoy your own experimentation more than anything at this point.

Oh, the people that discuss using HF (hydrofluoric acid) for etching and discussing its dangers, it is extremely nasty stuff when anhydrous. I couldn't read the link provided, but can add that an operatory accidentally opened a valve at our production plant when I worked in the fied and it reduced him to a pile of human jelly, a very sad time for the friend, family and not to mention hot water for the company. But aqueous HF is a reagent of choice used for etching -- glass, and widely used for this purpose with the appropriate precautions.

It is purported that a madame Voodoo lady in N. Orleans invented the HF based potion for meetinghers, labeling it "Love Potion No. 9", and some innocent 60's meteorite collector mistakenly took it and kissed all of the his meteorites in sight, later turning into a mindless hippy dude. The unfinished bottle remained in the unnamed Police station after he went after a policewoman who apparently slipped some in her pockets. It was rescued with the help of several listmembers. The hippy then sold the rest to Adam, but speaking for myself that will be Etching 201, and I don't think I'll be needing any soon.

While no doubt you will take all the appropriate precautions, don't forget to use glasses (or saftey glasses would be the way to go). A bit of HCl in the eyeball immediately washed won't do too much damage, but nitric and HF will.

Hope this is somewhat helpful...nitol'ly.

Saludos
Doug


VeIocity_at_aol.com escribe:

Okay, now I know that I can't procure concentrated nitric acid without being employed by an institution of higher learning---unless I want to lie to the suppliers and tell them I'm a Professor of Inorganic Chemistry at Anthrax University or something. I'm no good at lying.

So, following somebody's sage advice, I just bopped down to Radio Shack and picked up a pint of etching solution for about five bucks. Ferric Chloride, but I'm not sure what concentration. I assume that, even at full strength, FeCl3 requires more reaction time than does Nitrol. Anybody have experience with FeCl3, or give me an idea of how long I should allow it to react? BTW, I'm plan to use it on Campo and Canyon Diablo.

VeIocity
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Received on Mon 13 Sep 2004 12:54:51 PM PDT