×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Replacement for Picral?

Replacement for Picral?

Replacement for Picral?

(OP)
Someone mentioned on a recent post that their employer does not allow them to have picric acid, and unfortunately I am in the same boat. I work in the failure lab and deal mainly with plain carbon steels. Does anyone have a good recommendation for an etchant that can act similarly to picral? I understand that their is no substitute, but I would like to experiment with alternatives if possible.

RE: Replacement for Picral?

I had to look into this once. The real problem is solid picric acid is explosive if it dries out. Mixed solutions of picral and Villelas are, by definition, not dangerous because they are aqueous. New solutions should be mixed up if you ever see crystalization of picric acid but even in that circumstance they are perfectly safe. I would recommend either having a lab that can manage dry picric (I used a university lab at the time) prepare your reagents for you or buying the smallest quantity of picric acid you can get to make your reagents and safely discarding the picric crystals after you have made the etchants.

I would thus recommend you clarifying the real dangers associated with picric acid to your employer so you can safely use picral.

Aaron Tanzer
www.lehightesting.com

RE: Replacement for Picral?

I concur that dilute picric acid in something like Villela's reagent is relatively safe. However I have seen minute amounts of yellow crystal around the mouth of containers. Good practice is to wipe the cap and container mouth with a wet paper towel or cloth before resealing. It is grinding of dry picric acid powder between cap and bottle upon closing that can cause explosions.

RE: Replacement for Picral?

Why not use Nital instead of Picral?
Also consider mixing only enough Picral for each use.

RE: Replacement for Picral?

Ron,

Nital is the usual etchant for carbon and alloy steels, but it is essentially limited to revealing ferrite grain boundaries and general etching of martensite. Picral attacks the interfaces between ferrite and carbides, so it is useful for etching pearlite, bainite, and other carbide-containing microstructures. It is quite useful for etching dual-phase and multiphase steels, as well as tool steels. Another good application is for resolving weld fusion in steel tubes manufactured by the ERW process.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources