[meteorite-list] Etching solution

[MexicoDoug]

PS - if you don't have a hood or other exhaust, the methyl alcohol 
could also be dangerous becasue the liver breaks it down into toxins 
and you will inhale some of it.  That's another reason why I use 
ethanol in the oven, and frankly much more important a reason than 
saving a few pennies ;-)  You can consider the residence time of the 
toxins in your system to be as long as a week, so if your are doing 
etxching all day long,and are using methanol nital you definitely need 
a very well ventilated place, and methanol is sneaky worthy of a CSI 
episode of an innocent who done it since the syptoms and critical 
second hit can be stealth and barely naseaous for the first.

I know you didn't ask about methyl alcohol, but its good to see the 4 
common solcvent benefits/liabilities side by side, at least my take on 
it.  Anyway, you can see why ethyl alcohol iis usually preferred.  I 
just checkethe azeotrophes andisopropyl is only 2.3 C above ethanol 
mixtures so its ability to remove water would be very similar in the 
oven, the last thing to look up to decide theoretically approximating 
the penetrating ability as related to the surface tension of the 
alcohol (just a guess) what is the bestest alcohol would be to check 
the surface tension.  I just did and all three alcohols are nearly 4 
times that of water and within 5% o each other, so I would think that 
on penetrating ability they are probably all tied and would argue all 
factors considered ethanol is best since the worst you get is a 
standard hangover in standard use conditions, and to get a freak 
explosion from EtOH mixtures with acid is minimal compared to isopropyl.

Ferric chloride of course doesn't have the toxicity not flammability, 
but it stains like heck and with proper respect for the reagents plus a 
little experience, like everything else the risks are minimized.  
That's another reason to start with dilute nitric which I highly 
recommend until you have the bugs worked out of the etching "assembly 
line", ie, method you find best for your work.

Good luck,

Kindest wshes
Doug.


-----Original Message-----
From: MexicoDoug <mexicodoug at aim.com>
To: meteoritesnorth <meteoritesnorth at hotmail.ca>; Meteorite-list 
<Meteorite-list at meteoritecentral.com>
Sent: Thu, Jan 26, 2012 10:30 pm
Subject: Re: [meteorite-list] Etching solution


Craig,
Let me add (the message actually got away before being finished as I
write piecemeal and then send) that as far as etching it works fine,
but if you look at the series of alcohols, methyl (bp = 65 C), ethyl
(bp = 78 C) and isoproply alcohol (bp = 83 C), methyl alcohol
(methanol) is by far the safest until you get a lot of experience
working with these under a hood.  "Ethyl nital" is mildly flammable in
and Isopropyl nital is pretty dangerous since if can blow up in certain
conditions that aren't difficult to arrange.  Nothing to do with the
etching results which are left to trial and error, but rather the
safety which I should have mentioned.

While all the alcohols work fine, keep in mind two of the factors you
are working with are miscibility/penetrant ability and vapor pressure.
Vapor pressure you can estimate by boiling point - lower bp is a higher
vp.  The higher vp the quicker it will evaporate out, so methanol would
seem to have the advantage, thought it might form some azeotropes and
stay in longer, as could the rest without looking this up (no time at
the moment).

To the series of three common alcohols you could just add water bp =
100 and consider it almost as a continuim and play with the you like
which will influence drying time among other important parameters.  I
use methanol and later rinse with ethanol (cheaper for me), which is
the reverse of good drying practice I would think, but half of the time
I just use the diluted acid at 2 - 3 N.

Hope that was a better answer, sorry for not finishing the first
kindest wishes
Doug


-----Original Message-----
From: Craig Moody <meteoritesnorth at hotmail.ca>
To: mexicodoug <mexicodoug at aim.com>
Sent: Thu, Jan 26, 2012 9:42 pm
Subject: RE: [meteorite-list] Etching solution


Much appreciated Doug, Thank you!  I have lots of 99% around.

Craig 		 	   		

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