Do you mean the 'P-2' sulfuric acid-ferric sulfate etch used as a pretreatment for adhesive bonding of aluminum, as given in paragraph 7.4.2.2 of ASTM D2651, 'Standard Guide for Preparation of Metal Surfaces for Adhesive Bonding?'
http://www.astm.org/cgi-bin/SoftCart.exe/DATABASE.CART/REDLINE_PAGES/D2651.htm?L+mystore+ffte0991

The P-2 etch is usually used as a hex. chromium-free alternative to the FPL etch (Sulfuric Acid/Sodium Dichromate).  There are proprietary etches, also, as well as (unsealed) anodize pretreatments.

What are you trying to do?

Looking for the cleaning process for titanium before adhesion process similar to MIL-HDBK-691D, Pages 144-146, Para 5.3.XXXXXXX

Have seen reference to P2 etch, but can't see the similarity of the two processes. The part dwg calls for phosphate-fluoride method IAW hdbk mentioned,

I don't think the dentist office would want to do my product cleaning....LOL

Appreciate the help. No vendors have any substitute method.

Thanks, Everett

Boeing has switched to a SOL-GEL treatment for Titanium.

The proprietary Data is:
BSPS-07-001 SOL–GEL COATING FOR TITANIUM BONDING
BSMS-25-001 SOL-GEL Coating for Metal Bonding

The commercial product is SOL-GEL  AC 130.
Google search SOL-GEL and you can find info.
Can't give you the Boeing Data.

Very simply, the part is Grit Blasted, and SOL-GEL is applied similar to an Alodine application.
Then an Adhesive Bonding Primer is applied and the part is bonded like normal.
We have been using it very successfully.
And the EPA loves us for it. (No pickling fluid to mess with)

Thanks, I'll look into it as you suggest.