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Anodizing Titanium: electrolyte formula

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A. When anodizing titanium with a DC power supply, both citric acid and sulfuric acid can be used as electrolytes. Here are some of the benefits and disadvantages of using each:

Citric Acid:

- Citric acid is a weaker acid than sulfuric acid, which means it is less aggressive and easier to handle.
- Citric acid is non-toxic, biodegradable, and environmentally friendly.
- Citric acid produces a smoother and more uniform oxide layer than sulfuric acid.
- Citric acid is less likely to cause hydrogen embrittlement in the titanium.

- Citric acid is less efficient at anodizing titanium than sulfuric acid, which means it may take longer to achieve the desired oxide layer thickness.
- Citric acid may not work as well on certain titanium alloys.
- Citric acid may require higher voltages than sulfuric acid to achieve the desired oxide layer thickness.

Sulfuric Acid:

- Sulfuric acid is a strong acid, which means it is more efficient at anodizing titanium and can achieve the desired oxide layer thickness more quickly.
- sulfuric acid [affil link] is readily available and relatively inexpensive.

- Sulfuric acid is highly corrosive and requires special handling and safety precautions.
- Sulfuric acid can be toxic and harmful to the environment if not handled properly.
- Sulfuric acid can produce a rougher and less uniform oxide layer than citric acid.
- Sulfuric acid is more likely to cause hydrogen embrittlement in the titanium.

J Sal
- Tucson Arizona
May 21, 2023

Ed. note: Your e-mail address is bouncing.

A. From experience performing sulfuric anodizing of Ti to a very specific Prime standard (frozen tech plan), it can be done in a normal hardcoat anodize tank, using a pretty standard (=rather vintage) rectifier.
Presence of an aluminum anodizing burn-prevention additive (anodal EE, aa-200, etc) at the low end of manufacturer tech sheet recs does not seem to impact the success of the process whatsoever. I've successfully pushed through jobs with both, and with neither. Maintain Chloride in the ano tank <10ppm and have a pre & post process test specimen sent out for comparative Hydrogen Pickup testing.

As long as Aluminum is kept close to the normal 10 ppm target for aluminum anodizing, and Ti and Cl- contamination is low, the process will be fine. Hydrogen embrittlement should not be a given. If you see high H+ uptake on your test specimens, consider the immersion time / temp / strength of your caustic etch/clean prep step. This is a more likely suspect in this process.

Rachel Mackintosh
- Greenfield, Vermont
June 9, 2023

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Q. I want to anodize titanium using an alkaline anodizing bath. Who can give use the formulation of an alkaline anodizing bath. I want to get a gray coating.

Please help me.

UFF - Volta Redonda/RJ, Brazil

Ed. note: Since 1989 we've strived to build a legacy of aloha & camaraderie incompatible with anonymity; everyone is welcome to read anonymously, but is asked to use their real name & town when posting :-)

A. What is the application you have for the grey finish on the titanium parts? When I used to anodize titanium parts I used a supersaturated bath of trisodium phosphate [affil link]. The grey comes with too much current density and occurs when the process starts to break down. The grey I got was always by accident and it seemed to etch the surface requiring re-polishing of the piece and then re-anodizing. If you are looking for a visually pleasing shiny grey color as seen on some jewelry it is most likely niobium instead of titanium. I obtained this grey by heating the niobium with a torch and then lightly polishing with jeweler's rouge (polishing/buffing compound) [affil link]. With more information I might be able to give you better answers.

Good luck.

Howard Bailey
- Dresden, Germany

Thanks Mr. Bailey -- I think you are describing decorative anodizing of titanium, which is done from acid baths or TSP baths.

I suspect that the alkaline anodizing that Thamara is seeking is for engineering purposes (reduction of tendency to gall). Although it's covered by spec AMS 2488 [affil link], the shops who know how to do it keep quite mum; the formulation is not generic info yet :-(

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

Q. Does anyone know where I can get technical information on anodizing Titanium?

Ray Handwerker
- Marlboro, New Jersey

A. I remember a recent discussion on titanium anodizing right here on finishing.com but you could also consult the Metal Finishing Guidebook or any other standard surface finishing manual. A simple method of titanium anodizing involves a solution of sodium hydroxide and is very easy to perform. There are other electrolytes that can be used also. Good luck.

Megan Pellenz
Megan Pellenz
- Syracuse, New York

Q. Does anyone know how to chemically process two different type of surfaces on a small component. On this small component, one part is highly polished and the other part is a rough acid-etched surface. The transition is precise and immediate.

Dr. Norman Kwan
biomed. implants -. St. John's, Newfoundland, Canada

A. Polish and then mask off the polished part and etch the part that is to be rough. The shape of the part will partially determine the type of masking. You might consider masking and abrasive blasting the part that is to be rough. Process will depend on what you are calling "rough" and what the base metal is.

James Watts
- Navarre, Florida

A. Consider reviewing the following U.S. Patents: 3,959,091; 3,989,876 and U.S. Statutory Invention Registration H1207. Each of these articles discusses various methods for chromic acid anodizing of titanium.

Blair Smith
aerospace - Windsor Locks, Connecticut

Q. I am interested in what electrolyte is used to anodize titanium for subsequent adhesive bonding.

Paul Stransky
- Putnam, Connecticut
February 29, 2008

A. Depends what you want out of the bond. If it is structural then you may like to look at an alkaline system such as AMS 2488 [affil link]. If it is simply to get things to adhere you could consider sulphuric acid anodising, gives a very thin blue coating, nanometers thick.

You may consider other methods as well, such as wet abrasive blasting the surface or alkaline peroxide oxidation. The wet blast will not give a durable bond for hot or humid conditions, nor will the sulphuric acid anodising. If bonding for operations in hot and/or humid conditions you do need either alkaline anodising or alkaline peroxide oxidation.

Brian Terry
Aerospace - Yeovil, Somerset, UK

A. I have had success using a fluoride phosphate and using a chem film coating to improve adhesion for aerospace paint on titanium.

Jim Dedmon
- Ventura, California

Q. I am working in a scientific Iraqi center, becoming interested in surface engineering especially in anodizing process, so my question is: to anodize pure titanium, what is the effective procedures used? How can we decide what are the optimum requirements to pre-anodizing treatment. Thanks

Dr. Shrok Abdullah
Ministry of Science and Technology - Baghdad, Iraq
March 13, 2009

A. Hi, Dr. Shrok. A good starting point is probably AMS 2488 [affil link]. Unfortunately it won't tell you everything; alkaline anodizing of titanium isn't generic info yet. Good luck.


Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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