Anodizing titanium: amps, concentration, contamination, setup, problems

A. Hi Mark.

Probably not. ⇩

Titanium is anodized for one of two basic reasons"

• For decorative purposes like jewelry, titanium is anodized in a conductive solution like trisodium phosphate or phosphoric acid, even Coca-Cola. A very thin, transparent, layer forms on it which comprises a partial-wavelength interference coating. It can be done in thicknesses which will yield most colors of the rainbow, or it can offer iridescent oil-slick coloration if the thickness of the coating is variable. I imagine that it should be doable in a sulfuric acid aluminum anodizing solution, although I'm not familiar with it, but most colors probably require higher voltages than your anodizing rectifiers offer. Please search the site for "anodizing of titanium" for such facts and figures.

• For wear resistance and anti-galling, titanium is anodized per AMS 2487 and AMS 2488, which call for anodizing in a strongly alkaline solution, not acid.

Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.

Ed. note: Please see below for better answers from Willie and Rachel  🙂

A. Some readers say they've done it in Coca Cola, but dilute phosphoric acid or trisodium phosphate ⇦ on eBay or Amazon [affil link] is simpler and more repeatable; plus, using an opaque brown electrolyte instead of a clear one complicates the operation. It is obviously possible in sulfuric acid anodizing solution as we often see titanium racks for aluminum anodizing that become blue or purple, but I don't recall anyone posting that they've used an aluminum anodizing tank for titanium anodizing.

Goran Budija in topic 73/08 thinks 30 volts will be enough for blue. Jeremy Wyatt says 20 volts in topic 79/26, Paul Vernon says 28 volts on the page you are viewing. All say the grade of titanium and other operating parameters will affect the exact numbers. Several people call this "the first blue", implying that as you go to higher voltages and thicknesses, the color spectrum repeats and there will be a 2nd blue at some greater thickness where blue wavelengths once again get constructive interference while other wavelengths suffer destructive interference.

Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.

A. Mark

In practice, you should be able anodize titanium using the same bath as for aluminum. You'll be limited by your rectifier with respect to the colors you can obtain. Check your specification(s) for any restrictions.

A. Hi Mark!
At my previous job I used to run Blue Titanium to a GE spec in one of my Al hardcoat tanks. Can't remember which specification it was. We were quite transparent that it was a shared tank; GE and assorted Nadcap / AS9100 auditors were all fine with it provided that parts passed hydrogen pickup testing and the tank parameters within the Spec were met. All you need to remember is to add Ti testing to your maintenance schedule and keep it under 10 ppm. With the bulk of the work in that tank being Aluminum, our normal decants for Aluminum control were more than enough to maintain low Ti.

Ed. note: Thanks for the voices of experience, Willie and Rachel. I for one learned something new  🙂

A. Data for 6-4 Ti is not going to be the same as CP Ti. It also will not anodize as well because you are looking at 10% alloy. The aluminum will anodize at a much lower voltage than the Ti and will look different than the Ti. I think the Vanadium will not react or will dissolve. In short, I think you will get funky looking anodized parts.

You can get a how to do it manual from Reactive Metals Studio, Inc. in clarksdale , AZ

Jim

A. Ti6-4 surgical instruments are routinely anodized for color coding. The first blue color appears around 28 V. The exact relationship between color and voltage will vary with each setup. You will have to experiment. If you are using titanium clips to hold the work, the anodized layer on the clip will need to be removed mechanically or in a dilute (5%) HF solution (handle with care) between each run.

A. Search for "Titanium Anodization Color Spectrum" on your search engine of choice to find some great pictures that make the concept of first and second blue clear.
Some sites show approximate voltages to achieve each color - depending on tank make-up.
Speaking from experience, the colors on the EDC Specialties website line up pretty well with the results from using an anodize tank at around 300 g/l sulfuric acid.

(courtesy of EDC Specialties)

A. I have experience with anodizing small parts in titanium (commercially pure grade 1 and Ti 6Al 4V) and niobium, but nothing as large as your part. The current densities that I use vary from about 5 amps per square inch to less than an amp per square inch. I suggest that you start out on the lower range to avoid accidentally etching the piece. I use a solution of 3-5% by weight trisodium phosphate ⇦ on eBay or Amazon [affil link] in water. Keep the solution below 80 °F. I get more vivid colors on the 6-4 than the cp titanium, probably because it seems to take a higher finish easier. If you do not already have a suitable tank, you might try anodizing the piece with a brush saturated with the solution connected to the positive lead and the piece grounded to complete the circuit. You could use a painter's brush with the metal ferrule wired to the lead and then insulate the handle for safety. Artists use this technique to paint on sheets of Titanium.

A. Hi Dan,

If you're a hobbyist with a few small parts, there are simple kits. Or you can buy a power supply, some stainless steel for an anode, and a few beakers [beakers on eBay or Amazon [affil link] or plastic vats of some sort. The chemical can simply be TSP/trisodium phosphate ⇦ on eBay or Amazon [affil link] .

But I'm afraid it takes more info to properly answer that question. An anodizing line for an aircraft manufacturer might cost $5 million and still be considered an economical installation.

Luck & Regards,

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

A. It takes from 0 - 240 volts to get the variety of colors. Exact voltage control is mandatory to reproduce the same color. It will work on castings, but not quite as well. It is not as bad as aluminum or zinc castings to treat. Going from a hot rinse to a cold rinse a few times before you start will tend to fill the pores with water rather than chemicals, so there will be less bleeding when you finish.

A. You can get a kaleidoscope of colors when anodizing titanium. Solutions of various electrolytes are used: sulfuric acid, phosphoric acid, sodium hydroxide, ... As stated above, the voltage and time applied as well as electrolyte concentration will determine the color produced.

Titanium anodizing is one of those finishing processes that very closely approaches "art"; it takes a lot of leg-work, tank work, trial and error. There are some very good finishing houses that have perfected the process in terms of color matching, etc... Your alloy is a common one and should present no special problem to anodize.

A. I doubt if you will ever anodize with that strong of an acid solution. Try using a 7% trisodium phosphate ⇦ on eBay or Amazon [affil link] in distilled water and you will have enough amperage to anodize and not exceed the shutdown amperage. This will also allow you to get to your 100 volts. A plus, it is totally non hazardous. Reason, it is less conductive. What you have now is the crude equivalent of a dead short.

A. Titanium can be anodized according the voltage in sulfuric acid, the same as aluminium , and the colour may go blue to violet to yellow around 40 volts.

Once I used styrofoam in methyl ethyl ketone ⇦ on eBay or Amazon [affil link] to mask and it worked.

WHY DON'T YOU USE STENCIL ETCHING, IT MAY WORK (BUT NEVER TRIED).

GOOD LUCK AND GOD BLESS

A. There are two quite different types of titanium anodizing, Michael. There is a decorative anodizing used on jewelry that produces thin refractive films in attractive colors, which is usually done from solutions of mild acid, or TSP [trisodium phosphate ⇦ on eBay or Amazon [affil link] ]. And there is a heavy anodizing done from an alkaline bath for the purpose of making the surface less susceptible to galling; this is often done to spec AMS 2487 or 2488.

If you can tell us a bit more about what you want to anodize and why, we can probably help you narrow it down to which type you are looking for.

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

A. Michael,
You'll find many knowledgeable and kind people that take their time answering letters here. But regardless of how much help you may receive through this forum, without previous experience, it'll never be enough to set up a good level industrial operation almost from zero. It may appear very simple but involves years of hands-on and theoretical knowledge. I recommend you to hire a consultant.

A. Hi Nathan. Your question relates to one of those weird situations in the metal finishing world where a spec gives some requirements for the processing solution but not enough of them. Nowhere in my library of finishing books do I find anodizing of titanium mentioned, and AMS 2488 doesn't tell you what solution to use or how to do this process ... that is a trade secret :-(

I believe that Tiodize was once the only well known company offering the process, although a number of other shops offer it now, and a few consultants can help you. But successful AMS 2488 titanium anodizing involves tricks and solution compositions that are not yet generic knowledge. Sorry, but you have to either farm it out, or retain a consultant who knows how to do it, or do a painstaking gleaning of snippets of info from a computerized literature search and develop it independently.

Regards,

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

A. Rinse water cleanliness is my first thought. Are you using tap or DI for rinses? Are your rinses flowing or recirculating, and does the operator spray the parts down as they leave the rinse tanks? What is your limit for rinse cleanliness? Are there potential sources of contamination from either inorganic substances (such as drag-in from prior chemical tanks) or hydrocarbons (such as cutting fluid haze in the air from equipment nearby)?

If airborne hydrocarbon contaminants are an issue, they can also affect chemical tanks. I have personally seen this in desmut and anodize tanks, as our shop shares a building with a large machine shop, and we have to do more frequent tank changes as a result. The presence of scorched-looking, greasy dark brown or black residue at the waterline of your anodize tanks would be one indicator of hydrocarbon contamination.

A. Hello Jean. It sounds like no problem to me.

By the way, those warnings you refer to were in regard to anodizing of aluminum with SS attached, not titanium with SS attached. Aluminum anodizing is done in very corrosive sulfuric acid. I don't know what would happen if you immersed an assembly of titanium and stainless steel in a titanium anodizing bath; it might depend on what electrolyte you use.

Luck & Regards,

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