From:          Carl Sullivan 
Subject:       Ta Etch
Date:          Tue, 16 Jul 96 11:35:45 PDT
To:            MEMS@ISI.EDU
Reply-to:      mems@isi.edu

Hello,

Can anyone suggest a good "grain boundary etchant" for Tantalum?  Does anyone
have any experience with etching Ta to expose the grain boundaries?  Sorry in
advance if this is a trivial question.
Thanks
Carl

____________________________________________

Carl,

I would suggest consulting the ASM Metals Handbook Vol 9 Ninth
Edition entitled "Metallography and Microstructures".  There are
several suggested etchants for tantalum and tantalum alloys.  In the
past, I have had good luck with a mixture of Nitric Acid,
hydrofluoric acid and water based on the ASTM 161 or ASTM 209 cited
in this handbook.  You will have to adjust the levels of each
ingredient to achieve the desired etching effect.  Note that in some
cases, the etching occurs very slowly initially and then the etching
rate accelerates rapidly.  Be careful.  Godo luck!

Howard Last
Materials Engineer
Naval Surface Warfare Center
Indian Head Division
4140e@uwdesign.ih.navy.mil