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Electrode corrosion in anodizing bath

After a period of two weeks off (as a service period), I found out that in one of the two anodizing baths, the cathode electrodes were oxidized and dissolved. The concentration was 120 g/l H2SO4 and 4-4.5 g/l Al. The working concentration is 180-190 g/l H2SO4 and 5-5.5 g/l Al. I'm thinking of a ÄE^^{potential difference} change or short-circuit at the rectifier or both. There was no positive work electrode (aluminium) attached to the bath, but there was a water leak into the bath from the positive head's cooling spiral. What do you think happened?

Thanks
Vasilis K. Makkas
EUROPA PROFIL ALUMINIUM - Athens, Greece
2006

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Hello Vasilas. Are you using aluminum cathodes or lead cathodes (or something else)? Sorry, I don't know what you mean by "AE change". Why do you call the cooling spiral, "the positive head's". Is this cooling coil metallic, and is it not electrically isolated?

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2006

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2006

Hello Ted,
The electrodes are made from aluminum, and I did not write AE but potential difference (wrong language pack -- my mistake!). At the point that the aluminum is grabbed to the positive head-vise we have attached a cooling spiral because of the temperature that appears there, so I was not meant the bath's cooling suspension. Probably I had to make it clear from the beginning. I'm not sure but I think that there is an electrical isolation for the cooling coil that you mention -- at least THERE has to be!

     

Thank you very much for your time and I hope that I made you understand of the parameters
Vasilis K. Makkas
EUROPA PROFIL - Athens, Greece

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I strongly suspect that an electrical leakage current was the problem. It is possible that although the cathode is negative when the line is running, when there is no work in the tank the cathode is actually positive to a cooling coil or some other item in the tank. I don't think I'd suspect any chemical leaking from the cooling system to corrode aluminum.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2006