Non-Conductive Deposits on Expanded Metal Anodes for Chrome Plating Gravure Rolls
Q. As a commercial gravure printing facility, we chrome plate engraved copper cylinders for use in our presses. These cylinders can be as long as 3 meters. The active anodes in these chrome tanks are expanded metal conforming anodes composed of platinum coated titanium. There are also lead scavenger anodes for maintenance of the trivalent level. One of our divisions has recently experienced plating problems related to non-conductive deposit build-ups on the expanded metal anodes. A portion of the deposit was removed for analysis. Only a portion of the deposit was soluble in boiling aqua-regia. Analysis of the dissolved portion indicated the presence of lead and sulfur. We speculate that the deposit is lead sulfide. We are searching for a method to effectively remove the deposits from the anodes without damaging the platinum coating. Also, do you have any explanation as to the formation of these deposits, and is there a way to prevent or eliminate this problem?
Thank you in advance,Scotty [last name deleted for privacy by Editor]
A quick check of the solubility tables, "CRC Handbook of Chemistry & Physics" [link is to info about book at Amazon], indicates PbS should be readily soluble in most acids, especially aqua regia. My guess is that the insoluble part is one of the Pt oxides that is not soluble in aqua regia.
- Putnam, Connecticut
A. Dear Scotty,
The insoluble particle that you mention can be oxides of platinum.
This can be attributed to several reasons, but the most significant one can be improper coating/adhesion of oxides of platinum on titanium substrates.
With a correct platinized titanium anode I am sure the issue can be sorted out under the assumption that concentration, current density. etc., are all checked and found to be in order.
- Chennai,TN, India
A. If there is lead in solution, you may be depositing lead oxides which can be tenaciously adhered to the anode. Acid plus a light mechanical scrubbing (brushing) may be used carefully so as to minimize effect on platinum. Ideally, check the source of the lead and remove it. I do not know if you are using lead anodes in another section of the process.Barry L. Martin
anodes - Concord, Ohio, USA
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