Letter 13432

Etching titanium without Hydrofluoric acid  

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Hi. I am a Masters student in Chemical Engineering. I am working with the Titanium alloys especially Ti-6Al-4V. Earlier I used 50% Hydrofluoric acid to etch Ti-6Al-4V, but now I wanted to replace it with some other etchant because of its hazardous nature. Can anyone suggest an Etchant which does not involve HF acid.

Praveen Reddy K Depa
- Kingston, Rhode Island

Try replacing the hydrofluoric acid with Ammonium Bifluoride

Gene Packman
- Syosset, New York

Try oxalic acid as an alternative. It must be fairly concentrated, and used at an elevated temperature, but it does a very nice job of etching the surface of titanium. You will make titanium oxalate as a by product, which should be disposed of as required.

Tom Baker
wastewater treatment specialist - Warminster, PA

See Letter 13456.

Trevor Crichton R&D practical scientist - UK

I recall an expired patent describing the use of hydrogen peroxide with ETDA, usually at about 50 deg C. Etching is slow.

Ammonium fluoride or bifluoride is also slow since the dissociation constant of NH₄F is 5 orders lower than that of HF. Some ammonium fluoride based etchants use the addition of nitric acid -- that just bumps the fluoride ion concentration as well as providing an oxidizing agent and lowering the pH. One can argue the safety hazard of this mixture may be worse than using HF. The danger in HF is really the fluoride ions which are easily absorbed through the skin and forms insoluble fluorides of calcium. Care should also be used when handling ammonium fluoride.

Ian Yee
- Austin, Texas

For etching ti6al4v 10% HF, 5% HNO₃ and 92% H₂O with 10-20 sec immersion etching is the best way from my experience.

Venugopal K. A.
- India

This a is a query to Mr. Tom Baker who suggested using oxalic acid to etch titanium: Do you know of any way to extract the titanium oxalate from the oxalic acid solution after etching? We need titanium oxalate for an experiment and it doesn't seem to be commercially available.

William B Hankins
gov't - Menlo Park, California

The use of Ammonium Bifluoride (ABF) in place of Hydrofluoric Acid can be deceptively dangerous as, in H₂O, the ABF will cleave a hydrogen fluoride molecule creating hydrofluoric acid. . . the concentration of HF acid will be proportionate to the amount of ABF in solution and the ratio (20/57) of molecular weights. This is not a safe solution as many have been burned, some seriously with ABF solutions.

Mike Berg
fluoride chemicals - St Louis, Missouri

Try ammonium hydroxide, hydrogen peroxide, and water. Use volumes of 1:1:5. Maybe too vigorous if so then add additional water. Worked on removing titanium from evaporation systems.

Tim Dennis
ceramics - Bloomdale, Ohio

I would be extremely cautious in using ammonium bifluoride as a substitute for HF since, upon solublizing, it springs an HF molecule. The resulting HF concentration will be ~1/3 of the original Ammonium Bifluoride concentration.

Also, if using ammonium fluoride (AF) in an acid medium (ie HCL) the H+ ions will convert the fluoride to HF. This is common technology used in oil-well regeneration (in silica media)as AF and HCl are simultaneously pumped "down hole" with the evolution of HF in a safer (down hole) environment.

Mike Berg
fluoride chemicals - St Louis, Missouri

Reducing acids such as HCl and H2SO4 can be used as well as oxalic acid to etch titanium. Usually, you'll need elevated temperatures say 80~100 degrees C and fairly strong acid concentrations.They have the advantage of being much faster than oxalic.

Barry Martin
- Concord, Ohio, USA

We have successfully tried the hot sulphuric acid (temperature - 125 degree celsius) with a spoon of ammonium persulphate during every cleaning /etching step to remove the titanium.

ANUPAM SHARMA
- Delhi, India

If using HCL and H2SO4 to etch titanium, could Mr.Barry Martin suggest the etching time, etchant concentration, and etching procedure? We need the information.

Leo Wu
- Taipei, Taewan

Hi, i'm MOHIT DUDANI from CHENNAI, INDIA. Am trying to figue out the effect of acid treatment on titanium. Working presently with HF, H2SO4 and HCL acids. Can anyone please give me info on the effects of each acid on titanium and concentration used?

Mohit T. Dudani
student - Chennai, Tamil Nadu, India

Hello, Mohit. You are working with these acids on titanium so please briefly summarize what you are learning from your own experiments. That way it is much more likely that someone will share their findings with you. And they'll have a clearer picture of what your issues are too. Thanks.

Ted Mooney, P.E.  finishing.com Brick, New Jersey

Has anyone evaluated off the shelf products like Semco Pasa-Jell 107 or Turco 5578L. I am trying to etch titanium for bonding but having trouble finding a supplier for small quantities...

Jeff Lammers
- Melbourne, FL

Ed. note: sorry, Jeff, but the anonymity of the internet means that most times we print an inquiry asking for evaluations of brand-name products, shills start trying to post using fictitious names. Comparing brands is just a bad topic for the internet :-)

I recently started an assignment with the Center to assist in a project regarding removal of titanium from a HF/HNO3 chemical milling bath. I am particularly interested in learning about titanium chemistry in this environment to understand the various complexes that can form. Any information to lead me to this information would be very much appreciated.
Dick Poduska

Richard Poduska
- Rochester, NY, USA

I was hoping that Tom Baker could give some more details on etching with oxalic acid. My company uses a 10% oxalic acid solution and applies 12V DC current for 30-40 seconds (at room temp.) with results good enough to measure weld penetration on 300 series and 17-4 SS as well as MP35N. Using these settings for Ti, I get a copper-like surface with no indication of the weld nugget for penetration measurements. Are there any recommendations as to how I can improve my etching using oxalic acid at room temp?

Our company is not set up for major chemical handling, so I am looking for something that can be applied fairly easily with minimal equipment (room temp solutions ideal!). As such, hydroflouric acid is simply out of the question for our facility.

Brian Girouard
Mechanical Engineer - Burlington, MA USA