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-----Color of anodized titanium is inconsistent
Quickstart:
The 'color' of anodized titanium might be a little confusing to new readers...
If you look at a drop of oil in a puddle, or a CD/DVD you see a rainbow of colors -- but they are not 'real' in the sense that there are no pigments causing them.
Rather, half or so of the light bounces off the top of the oil film, and half or so penetrates the oil film and reflects off the water. White light is a mixture of light of many different wavelengths (red, orange, yellow, green, indigo, violet). The portion of the light that travels just that little bit further by penetrating the oil before reflecting is out of sync with the other portion, and this interference causes some of the colors to be cancelled and others to be amplified.
Titanium can be given a rainbow finish by allowing the thickness of the anodizing to vary, or it can be given a single color by making sure the thickness of the anodizing is constant, which in turn demands stable temperature, voltage, and all areas of the component receiving equal anodizing time.
Q. I am anodizing a sample of titanium, but color is not uniform and oxide layer hardness is very low and color is remove easily -- please help me for anodizing time and sealing.
Shahram Ghahremani- Istanbul, Turkey
2004
A. Hello, Shahram. It will be easier for people to tell you what's wrong if you tell them what you are doing and/or <email pics for posting>
We don't yet know the alloy, whether is acid anodizing or alkaline anodizing, the pretreatment steps, current density, temperature, etc.
Ted Mooney, P.E.
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finishing.com - Pine Beach, New Jersey
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Q. I am anodizing a sample of cp titanium (grade 2) at constant voltage, but color is not uniform (there are many colors on sample) and oxide layer hardness is very low and color is removed easily. Acid or alkaline anodizing, current density or temperature are not important for me, but just I need stable color and adequate surface hardness together. Also I do not know if sealing is necessary? Please help me for time, electrolyte, voltage.
Thanks
Shahram Ghahremany [returning]student university - Istanbul, Turkey
A. Hi again. Sealing is not necessary.
Although you say it is unimportant to you whether you are acid or alkaline anodizing, it's important to realize that there are 2 general types of titanium anodizing: decorative color anodizing and AMS 2488 alkaline anodizing for wear resistance & anti-galling. Topics 19805 and 23507 should be a good start to sorting out exactly what you are seeking and thus what general process you should be running, Shahram.
If you are trying to do decorative color anodizing in a single color, you probably need to reduce the voltage and increase the anodizing time so the thickness of the coating is consistent, because the thickness is what determines the color. Good luck.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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Q. Thanks a lot Ted, but also the color of sample is not uniform (in sulfuric acid bath) . The concentration of electrolyte is 160 gr/lit, do you think it is right? if I change the concentration of electrolyte or time of anodizing , will color be uniform?
Shahram Ghahremani [returning]- Istanbul, Turkey
2004
A. Color in titanium anodizing is extremely dependent on an exact voltage. A typical voltmeter is not precise enough for most needs. They are extremely accurate, but you can not read them close enough. You probably will need to use a proper digital meter to make the voltage reproducible (although no more accurate).
James Watts- Navarre, Florida
A. Hi again. James is probably right, but personally I've never heard of anodizing titanium in strong sulfuric acid. I'm starting to think you may be trying to anodize titanium as if it were aluminum :-(
If I'm right, it sounds like you are picking up stuff that refers to aluminum anodizing, and stuff that refers to alkaline anodizing of titanium while trying to do decorative color anodizing 🙂
Please tell us why you want to anodize it (pretty jewelry, wear reduction in machine parts, biomedical application), what pretreatment you are doing (you can't take oily, fingerprinted titanium and anodize it). If you can tell us what you want to anodize and why, we can hopefully point you to a document which better covers it.
Yes, anodizing time must be held reasonably constant.Good luck!
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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Need project assistance? $100/hr.
Titanium anodizing color uneven
Q. I am getting very uneven titanium parts anodized. The machinist bead blasted the parts and since then the parts won't anodize evenly. The parts look uniform but when we anodize them the color is an uneven mix of purple and blue. I have tried blasting them and re-doing them several times and even sent them to our other building to be anodized and got the same result. The parts are cleaned, then etched in deox, rinsed 3 times, then anodized. We sent the parts out and they came back looking nice and even but I would like to figure out how to fix this problem in the future. I have tried leaving the parts in the deox etch for 30 minutes just to see if there was a change but there was none. Does anyone know what causes this and how the other anodizing company was able to get the parts to look nice?
Dave ABULARACH- Norristown Pennsylvania
February 21, 2020
A. Hi Dave,
Looks like overheating locally. Try to minimize holders exposure to electrolyte, reduce electrolyte temperature, use slow swinging holders and very slowly raise voltage.
Anna Berkovich
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