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Anodizing of titanium: Type II alkaline vs. Type I decorative?



An ongoing discussion from 1998 through 2014 . . .

(1998)

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

Any advice would be appreciated.

J.H. Pennings
TNO Institute of Industrial Technology - Netherlands


(1998)

A. See AMS 2488 [link by ed. to spec at TechStreet] - the anodizing is performed in an alkaline solution of pH >= 13. Unlike anodizing aluminum, the colour is not uniform and not controllable (almost). Depending on the alloy (and solution?!), we are getting yellow to blue through grey appearance.
Max

Max Stein
captive metal finisher - Montreal, Québec, Canada


(2007)

Q. Alkaline Anodizing of Titanium Ti-6AL-4V. I am looking for the exact bath solution for what I have been told is a type II anodize per AMS2488D.

I understand that it is >=13 pH and that the temperature is controlled to +/-2 F and that voltage is the controlled characteristic, but WHAT is the chemical?

Vicki Dominguez
medical device industry - Huntington, Indiana


June 2, 2008

A. Hi, Vicki. I know it's strange and you'll say "how can that possibly be?", but ...

... even though the alkaline anodizing process is covered by AMS spec ...

... some of the details of the alkaline anodizing process are trade secrets. You have to figure out these details for yourself, or you have to retain a consultant who will give them to you; you won't find them in the literature or in public forums. Sorry, and admittedly it makes little sense, but there it is :-)

Regards,

Ted Mooney   Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



(1998)

! With titanium in a bath of trisodium phosphate [linked by editor to product info at Amazon] you get the most beautiful color of blue imaginable. All you need to do is to immerse the part, turn on the current and voilà , bright blue. Not gray but close?

Dave Fairbourn
- Sandy, Utah


(1998)

A. Thanks Dave. To minimize confusion, though, we need to tell the readers that there are two general types of titanium anodizing. The "alkaline anodizing" that Max speaks of is a heavy, wear-resistant, anti-galling surface for engineering applications. The acid or neutral anodizing you are describing is a very thin very colorful diffraction coloration for decorative jewelry and similar applications.

Ted Mooney, finishing.com   Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(1998)

A. A true grey from TSP (trisodium phosphate [linked by editor to product info at Amazon]) is not probable.

Brown, blue, silver, yellow, purple and green are possible at voltages up to 200. There are several different shades possible for each. Precise color requires precise voltage control. It anodizes nearly instantly. Surface prep makes a significant difference in the luster or look of the product. Does not need any further protection after anodize.

From 10% to 3% solutions are recommended.

James Watts
- Navarre, Florida


(1999)

Q. A magazine called Xtreme R/C Cars will publish an article on titanium anodizing in an upcoming issue. Sorry I don't know what month, but issue 4.9 I think. I am interested in titanium & alum anodizing, and would like to obtain a red color. Any info is greatly appreciated.

David Thomason
Glendale, Arizona


(1999)

A. The color red is not possible with titanium anodizing nor is black. Apparently neither exists in the spectrum created by the oxide layer formed on the surface. The color exists only as reflected light.

Dennis Rand
- Plymouth, Massachusetts


September 2014

A. Hi. Red "ish" or at least pinkish is possible, but all of the colors are low saturation pastels, not bright and vivid reds because of the source of the coloration. The anodized coating is actually translucent, almost transparent, and it is more "clear" than any particular color.

What actually happens is that when light hits the component, part of the light reflects off the surface of the anodized coating, and some of it penetrates the coating and reflects off of the non-anodized base of the component and back through the coating again. The result is that the portion of light that travelled through the coating travels further and is out of sync and the two reflected waves "interfere", canceling out some of the colors from the white light, leaving these pastel tones. Depending on what voltage was applied, the coating thickness varies, and thus the color.

Regards,

Ted Mooney, finishing.com   Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(2000)

Q. I am anodizing a 6al-4v titanium medical device blue, yellow & green. These parts are subjected to 250 °F steam autoclaving for sterilization. Some of the parts after two cycles of autoclaving (40 min/cycle)are beginning to change to the next color. (yellow - magenta, blue-clear). This is only happening in a few parts but I need help into why it is happening and how to stop it. If anyone has suggestions I would appreciate the help.

Jim Johnson, Sr.Design Eng.
- carlsbad, California


(2001)

adv.
We can produce and reproduce stable and controllable colors for titanium anodizing. Technology is ready for licensing.

6 colors of anodized titanium

You can see shades available on our web site. Black color can be obtained also, but this is a different technology.

anna_berkovich
Anna Berkovich
Russamer Labs
 
Pittsburgh, Pennsylvania



(2006)

Q. Dear Sirs,
I am a manufacturer of Orthopedic Implants made of S.S. 316L and Ti-6AL-4V ELI. I am looking for Anodize per AMS 2488 [link by ed. to spec at TechStreet]c Type I Colors (Pink, Gold and Green).

It will of great help to me if you can tell me the procedure for it.

Thank you.

Lokesh Jokiani
- Delhi, India


(2006)

Q. I am new to the anodizing process and am having problems anodizing titanium green. The pieces are about 2 and a half inches long and are a half inch wide. When I anodize these pieces in other colors I have very little to no problems. I was wondering if this could be environmentally affected (humidity) or is this a normal problem for larger pieces.

Terry Donnalson
hobbyist - Lititz, Pennsylvania

Bioscience and Bioengineering of Titanium Materials


May 2, 2008 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Dear sir,
I try to anodize titanium size 1" x 4" to pink and green color by use TSP and Borax but the color not pure, for pink color will have light blue and green color will have yellow. And it not shiny like gold,purple or blue that I do the same method. What solution I have to use for high voltage anodized and more method I should do?
Thank you and very best regards.
Thita M. ( from Thailand )

Thitaree Manosittisak
- Bangkok, Thailand


December 7, 2008

Q. We can do titanium anodising Green, Blue, Purple, silver, etc.
But yellow and black is nitride treatment, not anodising.
We need help of anodising red for titanium, as we now have pink color, but not red.

Fun Hsu
titanium - Ningbo, China

The Encyclopedia of Jewelry-Making Techniques


September 2014

Hello Fun. If you understand where the color comes from, as described above, you understand why pink is relatively easy and a bright red will not be possible. However, James Watts suggests that surface preparation is very important; and it seems to me that if the surface is highly polished and thus highly reflective before anodizing, you should get somewhat more vivid colors.

Regards,

Ted Mooney, finishing.com   Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


February 12, 2009

Q. Hi,

I wonder if someone could instruct me as to what solution is best to achieve an anodized silver finish on 6AL-4AV grade 5 titanium.

I would also appreciate information on setup and procedure i.e. precleaning procedure, anode/cathode ratio, suitable materials for cathode and jigs. I also need information on voltage/time and amps.

I would be very appreciate if anyone could provide this kind of information.

Simon Metaxas
- Birmingham, west midlands, United Kingdom


August 17, 2009

Q. We are doing golden, blue, pink, green, and yellow -- but how to do black colour?

manoj pavasiya
- Bombay, India


April 27, 2012

A. I see several comments pertaining to Grade II Titanium and obtaining green color.

Grade II in volume on racks can be vexing.
A common defect is a failure to obtain even color
Color can have a 'Ghosty" appearance when viewed inclined and under a bright light.

A coupon anodized, resulting in an uneven green color. When measured, the oxide thickness is uniform over the coupon.

Theories are, a change while anodizing of the um/Volt applied, and/or the um/second.

According to theory; these changes result in an anodized layer of mixed Titanium Oxide of TiO2, TIO3----X

Another theory is a change in cubic structure; i.e., anatase to rutile.
I call it The Grade II Blues.

Jon Quirt
- Minneapolis, Minnesota



May 31, 2012

Q. I am doing Ti-6AL-4V type II anodizing, but a few days ago during the process, the parts got a pink color and then the type II anodizing process stops in the parts but not in the titanium racks.

Tatiana Rios
medical instruments - Medellin, Colombia


June 2, 2012

A. Type II titanium anodizing will have uniform gray color. Some companies produce anodized parts covered by "fur" that require additional removal step. We produce hard anti-galling coating clean and ready for use. There is a possibility to grow the coating very thick for application where dialectic surface is required.

The color anodizing is always thin, and can serve mostly for color coding. The uniformity and consistency of color anodizing depend only on initial surface activation. This step can be conducted either electroless or under electrical current in a separate tank. Both methods are fine. As soon as the titanium surface is ready, it does not matter what anodizing solution you select for the final coloring. It can be oxalic acid or sodium wolframat or similar solutions available from the vendors. Be sure to final rinse the colored parts in diluted alkali solution, in order to prevent colors fading.

anna_berkovich Anna Berkovich
Russamer Labs
Pittsburgh, Pennsylvania



Why can't I achieve reliable green titanium anodizing?

September 17, 2014

Q. I am currently using sulfuric acid and sodium tungstate as my solution in my anodize tank. I get green sporadically. Need help on getting it all the time. My rectifier is 0-100 volts. I was getting it at 86.5 volts but now I am all the way up into the 90 volt range and I keep losing green. Need help.

Penni Higgens
- Perkiomenville, Pennsylvania, USA


October 2014

Hi Penni. Jon Quirt has specifically discussed the particular problem of green anodizing above and, although he doesn't offer an exact answer, he does offer food for thought. So the discussion will probably be more enthusiastically re-addressed if you try to incorporate his previous response into your question.

Also, please see letter 7926, "Anodizing titanium to green color -- Q&A's". Good luck.

Regards,

Ted Mooney, finishing.com   Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Can't obtain light grey in titanium anodizing

October 3, 2014

Q. Hi, we are doing anodizing on medical device implants, and we do type II, and achieve all the colors except Light Gray titanium-like colour Kindly help us for this.
We are doing thicker hard gray colour already.

Awaiting your prompt reply,

Regards
Raju

Raju Patel
- Ahmedabad India


October 2014

Hi cousin Raju. Penni is standing in line ahead of you, also awaiting a prompt reply to a problem that you imply that you've already solved. Can you offer her any tips while we await an expert who can help you? Thanks!

Regards,

Ted Mooney, finishing.com   Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


October 9, 2014

Grey type II anodizing for color or for hard surface quality - these are completely two different processes.

Grey color can be obtained in sulfuric acid. This process is easy and fast. Customers for disposable medical parts are quite happy with such anodizing.

Grey hard titanium anodizing 2488 type II is more complicated, requires proprietary conditions. Some companies advertise their equipment and chemicals for hard titanium anodizing. However in reality they hardly produce reliable and repeatable coating on more than one titanium part.

Concerning green coloring - anodizing green goes on high voltage (starting 70V). In order to reach this voltage without gassing, titanium surface must be free of iron (from cutting tools), and must be heavy saturated by fluorides. Saturation can be conducted either by electroless method, or under electrical current is special proprietary solutions. Some titanium alloy are not prepared well for coloring by standard electroless methods, and require careful preparation in electrolytical bath. Such bath does both -- removes remaining of iron, and loads titanium with fluorides.

adv.
Contact us for more information.

anna_berkovich Anna Berkovich
Russamer Labs
Pittsburgh, Pennsylvania


September 29, 2014

Hola, la mayoria de los anodizadores de titanio utilizan soluciones acidas, pero nosotros estamos utilizando soluciones alcalinas, el color del anodizado es mas firme pero esta desfasado con cerca de d0s volts, por ejemplo para el azul con acido es de 18 volts, mientras que con solucion alcalina es de 20 volts, con soluciones alcalinas es mas lento el anodizado y lo puedes controlar mejor.

victor solis neri
- guadalajara, jalisco, mexico

----
Ed. note: Hola Victor. ¡Gracias!
We appreciate your response, but we've found that if most of the readers and the site moderator don't understand the messages, the forum just doesn't work. I wish I knew Spanish, but I don't. I can basically understand your posting, and I thank you for it, but I can't pretend to actually understand Spanish :-(
Please try to post in English. Thanks again!



January 17, 2015

A. Type I anodizing is color spectrum processing on titanium.
Type II anodizing is the hard coat process on titanium.
Implant alloys are mainly Ti6Al4V material specifications. The process is listed under AMS 2488 I believe.

Type II Ti hard coat processing is very much proprietary in both process and chemistry parameters. Takes a bit of patience and research but it can easily enough be figured out. I put together two different bath chemistries that produce high production numbers of high quality product. I can process many pieces at the same time with no shade variance in the grey coating. Most OEM's are looking for a lustrous dark grey in the final finish.
If you anodize then you already know that green is the hardest spectrum to maintain repeatability on. Different chemistries produce different colors ant different voltages. My green spectrum hits between 92 and 95 volts before I go into pinks. Hot pink as well. Blue ghosting or spots I think is the biggest issues with the greens. Teals are within a very small voltage parameter and have nothing to do with the blue problem in green. Oxide growth is uniform so surface roughness can play a factor in higher voltage colors. Shorter etch times can leave the surface too smooth to achieve the perceived green color over the entire substrate. Too rough of a substrate can cause interference in light refraction because the peaks and valleys are too far apart for an even refraction. The oxides created are still uniform in thickness which creates highs and lows in the oxide finish causing the interference or crossing of rays that may appear as spotting or ghosting. Maintaining close tolerances in chemistry and voltage parameters is very important in achieving green repeatability. I run several shades of every color to include green. Organic and inorganic oxide removal before the color tank is a major player in high voltage green. Most cleaners will not remove the organic contaminant of the oxide formed due to heat created in the milling processes of the part. I process implant geometries so etch removal of the contaminants can cause undersized critical dimensions. My etch rates are slower so pre-cleaners and deoxidizers are a must before etching even begins.
I believe the grey color you are looking for in type I Ti color anodizing is called grey green. I run that color quite often. In my chemistries, it's found between silver and seafoam. Cold baths create better colors!

Brad Arnold
Medical device surface finishing - Memphis, Tennessee, USA

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