-- The Home Page of the Finishing Industry
23+ years of serious education, promoting Aloha,
& the most fun you can have in metal finishing smiley
    no popups, no spam
on this site
current topics
topic 10204

Film Formation on Lead Cathodes for Sulfuric Acid Anodizing


I am seeing a pink colored, almost copper looking film forming on lead cathodes in my sulfuric acid anodize tank. I use titanium cooling coils in the tank. The film seems to form on the cathodes when I am not using the tank for production. When I start to anodize, the film gradually comes off the lead cathodes and you can see gassing around the cathodes after the film dissappears. I have problems with the anodize coating absorbing a dichromate seal and am wandering if it might be caused by an improper film formation on the anodized surface due to the film I can see on the lead cathodes. The bath concentrations and temperatures of the anodize solution and dichromate seal are within the operating parameters.

Randy Bland
metal finishing - Rockford, Illinois, USA


You are very probably anodizing at least some high copper alloy aluminum. Copper forms a copper sulfate. Your tank probably has a light blue tint to it. The copper is immersion plating on the lead. It is a nonadherent film and appears to "burn off" when current is applied. I always thought that since the lead is negative, that it would plate off. Evidently the hydrogen liberated at the cathode is reacting with it and dissolving it.

James Watts
- Navarre, Florida


I concur with the diagnosis of copper but I'll bet my standard coffee and donut that the majority of copper is coming from your bussing! Change all cathodes and bussing at the tank to aluminum 6063T6. Easy and inexpensive update of an operation.

drew nosti
Drew Nosti, CEF
supporting advertiser
Ladson, South Carolina


I agree the film is copper.

You can either remove the cathodes when they have the film on it and scrub them clean.

Or throw the anodise solution away.

Just a thought but do you check the 'aluminium' content of the anodise solution as this will show some copper content.

Martin Trigg-Hogarth
Martin Trigg-Hogarth
surface treatment shop - Stroud, Glos, England

This public forum has 60,000 threads. If you have a question in mind which seems off topic to this thread, you might prefer to Search the Site

ADD a Comment to THIS thread START a NEW threadView CURRENT TOPICS

Disclaimer: It's not possible to diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations may be deliberately harmful.

  If you need a product/service, please check these Directories:

JobshopsCapital Equip. & Install'nChemicals & Consumables Consult'g, Train'g, SoftwareEnvironmental ComplianceTesting Svcs. & Devices

©1995-2018, Inc., Pine Beach, NJ   -   About   -  Privacy Policy
How Google uses data when you visit this site.