Picric Acid in the Met Lab? 1

[dbooker630]

I seem to recall a few threads on this topic but I'm not sure. I recently was audited by our safety person who was shocked when I told him I had picric acid in the lab. Reportedly use of the compound was banned in our company labs.

Anyway, I don't have the solid form but rather a 1% aqueous solution which I understand does not have the explosive properties that the crystal form does. When I use the solution I wipe the bottle top with due care before replacing the cap. So I have challenged the safety person on my continued use of the solution, as it would also be costly to dispose of this product with the current regs.

My question is, what are other metallurgists using to replace picric? Most of the time on routine lab work I use 2% Nital but there always is that difficult heat treat problem that pops up once in a while where picric is a good analytical aid. Thanks for your help.

 

[arunmrao]

Picral is a good etchant and I have never had issues handling it.Of course I am not from USA!!

 

[TVP]

Your safety person is overly cautious. Picric acid is very useful for etching a variety of metals like steel and magnesium, and proper precautions can be easily implemented to maintain a safe work environment. Check out ASTM E 2014 Standard Guide on Metallography Laboratory Safety or the following link from Buehler for more information:

http://www.buehler.com/technical_information/Buehler Book/laboratory_safety.pdf

 

[JLSeagull]

I searched the standards for TRINITROPHENOL and Picric. A couple of old Army standards that used picric were deleted, other standards were withdrawn. The only two active standards pertained to liquid chromatography to detect picric acid in air and one on wine.

Check your methods that use picric and update with the current versions.

 

[NickE]

JLSeagull -- There is no way to replace the Picric Acid in Picral Etchant (or in Viella's Reagent). There are times when only Picral or Viella's will do. To be properly supplied Met-Lab's must have Picric Acid.

 

[redpicker]

While the dangers of Picric acid are real, IMO they are overblown (and misdirected). I've used the stuff for over 25 years and, in my younger days, even tried to get an exothermic reaction out of it. I have been told, as a dehydrated metal salt, it can form a contact explosive, which I do not doubt. But, using the procedures you mention, you should not have a problem with explosion.

I don't seem to hear anyone ever mention the health risks of the stuff, however. It can be directly absorbed by the skin and builds up in the liver. Not good to be around. I am definitly much more concerned about the health risks over the explosion risks. But, with careful handling, neither risk is all that great.

As far as I know, there is no substitute, although you might want to search out a metallography board to see what they would have to say. I'm like you, I'll use nital first, but picral can reveal a whole lot that nital won't.

rp

 

[unclesyd]

Like any other chemical if used properly there is no problem.
Our group fought the same battle several times. It wasn't only Picric Acid but almost every other etchant in the cabinet. Every time the safety department added a new person they went on tare to get rid of hazardous chemicals, especially in the Metallurgical Lab since we weren't traditional chemists or technicians.

Early on I always liked to point them to the Medical Department to check their storage cabinet. There were several gallon bottles of Picric Acid solution used to treat burns, especially chemical burns from Hexamethylene Diamine, a very strong organic base.
I still have a first aid kit from the the 50's that has several ampules of 1% Picric Acid in Alcohol, a general antiseptic at the time.

 

[dbooker630]

Thanks to all for your responses. I've got some more ammunition now.