Subject: Re: Chromic Acid Cleaning Solution
From: rtore00@pop.uky.edu (Professor Robert Toreki)
Date: Dec 18 1996
Newsgroups: sci.chem

In article <32b7839f.557083@news.ucs.mun.ca>
colinc@morgan.ucs.mun.ca (Colin Cameron) writes:

> On Tue, 17 Dec 1996 17:09:03 -0600, Subramani Iyer
> <siyer@bobo.acs.uiuc.edu> wrote:
> 
> >hi netters:
> >
> >Where would I find the recipe for making chromic acid
> >solution for cleaning glassware?  
> 
> A nice alternative is conc H2SO4 + 30% H2O2 (in approx.  3:1 to 4:1
> proportion respectively). It does a great job on those glass frit
> crucible funnels! Be careful though, it spits hot H2SO4, so be sure to
> keep it covered.

     That's going from bad (carcinogen and environmental no-no) to
worse.  Some of the worst lab accidents around have been caused by
using this so-called "piranha solution".  Yes, it cleans glassware
really well, but it also reacts violently with many chemical residues. 
If you do you use this concoction only generate small amounts at a time
and KEEP IT AWAY FROM ORGANIC SOLVENTS.  Do not make the mistake of
mixing this stuff with acetone (as you might accidentally do cleaning
frits).  Treat it with a VERY healthy respect -- cleanup time is when
we tend not to pay attention to things and is therefore when accidents
are most likely to occur.

     "Safer" alternatives are KOH/ethanol as suggested already and
NoChromix (a packet you add to a bottle of sulfuric acid).  Actually,
soap and water removes most stuff.

     I did have a former colleague who regularly used piranha solution
with an added dash of Clorox (5% sodium hypochlorite, i.e. bleach).  I
have to admit that it did clean well.  Plus it gave a really neat
greenish cloud of Cl2 to admire and breathe...

Rob

Subject: Re: Chromic Acid Cleaning Solution
From: colinc@morgan.ucs.mun.ca (Colin Cameron)
Date: Dec 19 1996
Newsgroups: sci.chem

On 18 Dec 1996 14:26:45 GMT, rtore00@pop.uky.edu (Professor Robert
Toreki) wrote:

>     That's going from bad (carcinogen and environmental no-no) to
>worse.  Some of the worst lab accidents around have been caused by
>using this so-called "piranha solution".  Yes, it cleans glassware
>really well, but it also reacts violently with many chemical residues. 
>If you do you use this concoction only generate small amounts at a time
>and KEEP IT AWAY FROM ORGANIC SOLVENTS.  Do not make the mistake of
>mixing this stuff with acetone (as you might accidentally do cleaning
>frits).  Treat it with a VERY healthy respect -- cleanup time is when
>we tend not to pay attention to things and is therefore when accidents
>are most likely to occur.

I agree completely. This cleaning solution is potentially hazardous,
but its high reactivivity with organic residues is something to be
desired (you DO want to get rid of it, right?). I should have
mentioned in my earlier post that using this mixture to clean
glassware soiled with residues containing metal should certainly be
undertaken with extreme caution; they tend to be quite violent
(catalysis, perhaps?). I would never recommend making a bucket of this
stuff, but rather generate it in situ, in a glass funnel for example.
(It works nicely for NMR tubes as well, but extreme caution is again
needed as they tend to spit a lot. Point it away from yourself,
towards someone you dislike if you wish.) However, I would disagree
with your claim that H2SO4+H2O2 is worse than chromic acid as the
latter has environmental concerns in its disposal.

>     "Safer" alternatives are KOH/ethanol as suggested already and
>NoChromix (a packet you add to a bottle of sulfuric acid).  Actually,
>soap and water removes most stuff.

Soap and water is good, and a base bath is better, but sometimes you
need something else to get your beakers whiter than white! :)


------------------------------------------
Colin Cameron  colinc@morgan.ucs.mun.ca
Dept. of Chemistry
Memorial University of Newfoundland
Lab: C-5013  Phone (709) 737-4785
------------------------------------------

From: Sean O'Brien <nobody@nospam.net>
Newsgroups: sci.chem
Subject: Re: Piranha Solution
Date: Tue, 08 Apr 1997 12:43:17 -0500

There are some interesting aspects to this extremely dangerous mixture.
First is the temperature spike.  As you mix acid and water of course
the temperature will increase.  Since 30% H2O2 is 70% H2O this is a
key effect, however if you are using ultrapure H2SO4 and H2O2 the
temperature spike is much lower.  With laboratory grade reagents it
is quite easy to achieve a 170oC solution within 1-2 minutes after
mixing.  However using ultrapure top quality semiconductor grade
reagents the temperature spike is closer to ~90oC.  While this
still is dangerous I would think the cooler solution would be much
less dangerous, the extra 80oC would accelerate reactions from moderate
to explosive.  

Since virtually nobody has access to such ultrapure chemicals piranha
should be considered deadly explosive.  However, it is used with
virtually no ill effects throughout the semiconductor industry.  An
interesting alternative is to bubble O3 into H2SO4 and heat it to about
140oC (since there is no heat of mixing).  This solution will last for
days while a true piranha is dead within 1-2 hours.  While it may still
be as dangerous the requirement of a heater makes a huge difference in
controlling it.

Sean



Peter Culshaw wrote:
> 
> Has anyone had any experience with this stuff, what I especially want to
> know is how dangerous it is, as if we move to use it routinely then less
> technically qualified people may be working with it.
> 
---------1---------2---------3---------4---------5---------6---------7
Sean O'Brien    email: sobrien@spdc.ti.com    Texas Instruments

From: "Rebecca M. Chamberlin" <rlmiller@lanl.gov>
Newsgroups: sci.chem
Subject: Re: Piranha Solution
Date: Tue, 08 Apr 1997 13:05:27 +0000

Sean O'Brien wrote:

> There are some interesting aspects to this extremely dangerous mixture.
(snip)
> Since virtually nobody has access to such ultrapure chemicals piranha
> should be considered deadly explosive.  However, it is used with
> virtually
> no ill effects throughout the semiconductor industry. 

And therein lies the crucial caveat:  IF you are using it under
"production" conditions and you can be CERTAIN that it will NEVER come
into contact with organic solvents, then it is relatively safe.

However, using it in an R&D lab is asking for trouble.  A classic lab
accident with piranha solution occurred at Cornell in 1986 or so.  The
grad students in one lab used to rotate responsibility for cleaning all
of their glass frits by running piranha solution thru them (using "house
vacuum") into a filter flask.  One student made the mistake of leaving a
trace of acetone in the flask.  When the piranha solution hit the
acetone, it went BLAMMO and a million pieces of glass embedded
themselves into her face.  Thank heavens she was wearing her safety
glasses or she would most likely be blind now:  the lenses in her safety
glasses were shattered but still intact in the frames.  The chemistry
department took a photo of the glasses and used it in their "Are you
wearing your safety glasses?" poster for years afterward.  Not
surprisingly, the student decided to leave chemistry after her
hospitalization.  

I will take the liberty of quoting an older post from Rob Toreki

	[[ snip -- see above ]]

Becky

Newsgroups: sci.chem
From: B.Hamilton@irl.cri.nz (Bruce Hamilton)
Subject: Re: Pirahna Solution
Date: Tue, 08 Apr 1997 19:22:18 GMT

Sean O'Brien <nobody@nospam.net> wrote:

>There are some interesting aspects to this extremely dangerous mixture.

[ interesting thermal effects deleted ]

I, and probably many other analytical chemists use a modified version
frequently during Kjeldahl digestions. We add about 0.2-0.5g of organic
sample, 0.8g K2SO4 + small amount of Cu salt, 10 mls of conc. H2SO4 and
cautiously add 3 mls of 30% H2O2 - allowing a few seconds for the 
foaming to subside a bit after each ml or so. We then put the tubes 
straight into a heating block at 390C - it can be quite vigorous, but 
after 30mins most of the organic material has strangely disappeared ;-).

          Bruce Hamilton

From: rtore00@pop.uky.edu (Professor Robert Toreki)
Newsgroups: sci.chem
Subject: Re: Piranha Solution
Date: 9 Apr 1997 14:00:06 GMT

In article <334A4298.C1C@lanl.gov>
"Rebecca M. Chamberlin" <rlmiller@lanl.gov> writes:

(snip)

> However, using it in an R&D lab is asking for trouble.  A classic lab
> accident with piranha solution occurred at Cornell in 1986 or so.  The
> grad students in one lab used to rotate responsibility for cleaning all
> of their glass frits by running piranha solution thru them (using "house
> vacuum") into a filter flask.  One student made the mistake of leaving a
> trace of acetone in the flask.  When the piranha solution hit the
> acetone, it went BLAMMO and a million pieces of glass embedded
> themselves into her face.  Thank heavens she was wearing her safety
> glasses or she would most likely be blind now:  the lenses in her safety
> glasses were shattered but still intact in the frames.  The chemistry
> department took a photo of the glasses and used it in their "Are you
> wearing your safety glasses?" poster for years afterward.  Not
> surprisingly, the student decided to leave chemistry after her
> hospitalization.  

As it appears that Becky, I and others have not quite gotten the point
across, let me drive it home one more time.  While you can usually tell
a conversation among chemists has gotten lame when they start swapping
lab accident stories, it is important that you **understand** that the
risk of using this solution is nowhere near the reward.

What Becky is writing about is 100% true.  I saw it.  It happened.  It
could just as easily happen to you.  Read this and then ask whether a
clean frit is worth this.

I was the first one to get to scene of the above incident.  We heard a
sound like an M-80 (about a quarter stick of dynamite) from two labs
away.  We got there within about 5 seconds to find her on the floor
halfway across the room surrounded by a large pool of blood.  The
filter flask that she was using turned to dust; we never found a
fragment larger than about 2 mm even though it had been wrapped in
heavy black electrical tape.  The metal 3 prong clamp that held the
flask sheared off at the point where it was clamped to the latticework
in the hood.  A row of glass cabinets along one wall were peppered with
holes from the shrapnel.  The lab had one of those 100 mm diameter
glass drainpipes running vertically on the wall opposite the hood
(about 8-10 m away) -- the pipe cracked in the middle ...we believe
that it wasn't from shrapnel, but from the compression wave of the
blast.

The student was wearing rubber gloves, a thick sweater, a lab coat, an
apron and safety glasses at the time of the explosion.  The hood was
down part way and saved her from catching most of it in the face.  The
arm holding the frit caught most of the damage -- the glove was
completely flayed and her arm had several hundred small bits of glass
in it as well as several fairly large lacerations.  She had a wound
about 20 mm in diameter just next to her jugular vein.  At least one
piece of glass went through her cheek. She (and everything else) was
also covered with hydrogen peroxide and sulfuric acid; something that
we didn't realize until much later because we had no way of knowing
what had happened.  I think the bleeding stopped more because she went
into shock than from the pressure were were applying in two different
places.

She spent the next six hours having tiny bits of glass picked out of
her arm, neck and face.  I'm told that you continue to have those work
their way out of your skin for the next several weeks after such an
incident -- that you sweep your good hand across the arm and cut
yourself on the glass sticking out of your own skin.  This student had
some nerve/tendon damage and lost a bit of the motion in one or two of
her fingers; I can't recall if she had any hearing loss or not.  All
things considered, she got off pretty lucky.  And yes, she did leave
the program a short time after.

Now consider this:  10 minutes later and the rest of my research group
would have left for dinner.  She was working ALONE in her laboratory,
"just cleaning up".  Maybe she could have gotten to the phone on her
own...when I got there she was trying to get up, but not very
successfully.  Ever try to stand up in a pool of your own blood and
sulfuric acid on a linoleum floor while dazed and injured?  Me neither,
but it certainly didn't look very easy.  Think about that the next time
you are working a late night alone.

The odd thing here is that if she hadn't been working alone there would
have been many other injuries in that laboratory.  We found one large
chunk of glass imbedded in a bookcase over someone's desk.  If the
owner of the desk had been there he would have caught this fragment
with the back of his neck.  I can not stress enough how **stupid** it
is to put a desk or glovebox opposite a fume hood (or having a desk in
a lab, but that's not always avoidable).  Look around your lab and see
if you have that configuration...it's scary.  And the next time you see
someone without their safety glasses on, help them find a pair or make
them leave.  It is one thing to be an innocent bystander, it is another
to be a stupid bystander.

BTW, the shattered safety glasses Becky is referring to were from a
separate accident at Cornell involving a vacuum line explosion, but
that's another story and I only know it secondhand.  Part of their
rather effective campaign to make you think about safety.

Let me just end with the question I posed at the beginning:  Were a
batch of clean frits really worth all this?

Rob