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Why Did My Titanium Anode Case Turn Purple when Plating Sulfamate Nickel?

I am using sulfamate nickel bath to electroform optical discs. All hardware that I use is titanium, and after a short ramp, I use 100A(~24V) with a cathode surface area of 0.25 ft2.

Recently, an anode case was dumped and cleaned, and to my surprise, it was completely PURPLE inside and out. Since there are 6 baths running on the same solution, I don't think that the problem lies there. It doesn't appear to be burnt. Does anyone have any suggestions for why it turned this color?

Dave Chullino
- Terre Haute, Indiana, USA
2000
publicly reply to Dave Chullino

You have two something weirds. I have never seen titanium that would stand 24 volts anodic in a sulfamate nickel tank. It self destructs starting at about 9 volts or slightly lower. 400 amps per sq ft is an awesome amount of power that normally requires exceptionally turbulent flow to not tree like mad. Lacking any other information, I would have to guess that you somehow anodized the titanium, as deep blue or purple is the color formed in sulfuric acid at about 20 volts.

James Watts
- Navarre, Florida
2000
publicly reply to James Watts

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A. The problem that you have mentioned is puzzling indeed. I have seen purple shades on titanium in conditions when excessive current is passed through it causing it heat up or may be a loose connection that causes the heat buildup. But as Mr. James Watt has mentioned about titanium self destructing at 9 volts, I use it regularly at 18 volts for the last few years. The CD is around 100 amp/sq ft. I think it is the high CD that may have caused it. Nitin Kibe - Pune, India 2000 publicly reply to Nitin Kibe A. I have seen more than one anode basket destroyed by about 9 volts anodic. Being able to go to 18V anodic must have been done with a very low chloride level. If not that, I have no clue. James Watts - Navarre, Florida . publicly reply to James Watts