Porous Pots to Clean Chrome Plating

A. Porous pots do exactly the same thing, and function in exactly the same way, as membranes. Now, if only I really understood how membranes work, I'd be getting somewhere

You put a cathode in the pot, and an anode around the outside, and it oxidizes trivalent chrome back to hex chrome, while simultaneously attracting the iron and other metallic contaminants. I understand that chromic acid remains an anion while the other metals are cations. Exactly what the membrane or pot does for the electrode process I don't claim to fully understand, but I presume that hex chrome can't pass through while the cations can.

A. We had a chatroom discussion about this a while back, and it turns out that the AESF sponsored a research project on porous pots. Email them (www.nasf.org) and ask for a copy of the report. The scientists spent some time in the report explaining the mechanism, and had data about the pore size and anode and cathode ratios that are important to the proper operation.

A. Check the December 1977 issue of "Plating and Surface Finishing" (AESF trade journal). You will find an excellent article about porous pots, how they work, and tips on usage.

Ed. note: Thanks, Jeff!

A. You do not say whose pots they are or what size they are or the total amount of trivalent you are trying to convert in what time period. Also , how new are they. The pores can plug up and efficiency drops way off. I suspect that your reaction with the plastic is generating a lot more trivalent than you think. An obvious solution is to go to more pots if three is not enough. On chrome plating tanks, we just used the plating solution in the pot and dumped it when it was slimy. You may have to dump the inside more often than you are doing now.

What does the vendor of the pot have to say?

A. Not knowing how high your tri-chrome has reached my suggestion would be to increase your sulfuric to 30%. 15% maintains your opt range once it's reached however 30% will help you to begin to lower your tri chrome.

A. I seriously doubt if you can make one cheaper than you can buy a rudimentary model (from suppliers who make this product).

A. If you really want a cheap system go to your garden centre and get a flower pot - not the plastic type but a proper old ceramic type. Thoroughly wash it with acid and alkali cleaners and leave it in soak for a few days, regularly changing the water. Stick a rubber bung in the drain hole and hey presto - a cheap porous pot. I have used one for a divided cell in a small plating bath using trivalent chromium without any major problems. I don't know how long the pot will withstand the process, but in the short term it worked. Don't tell the membrane manufacturers though, they may corner the market for flower pots and upset us gardeners!

A. Dear Jonathan,

I heard that other than porous-pot system, in Northern America & Canada even Europe nowadays a lot of Hard Chrome Platers are using sort of Ion-Exchange technology to reduce Fe content in their Hard Chrome solution to maintain the efficiency, roughness, waste water treatment cost, etc.

Might be you can contact your chemicals or machinery supplier in your city/country.

Good luck

Best regards,

A. Hi Greg. Certainly a glazed pot could not work, but Trevor says an ordinary clay flower pot can serve as a membrane for an experiment if it holds up to the chrome plating solution. Please google "porous pot for chrome plating" and consider purchasing a commercial system for the purpose.

We don't know where you heard about ceramic pots for removing tramp metals from the chrome tank, so we don't know what you are aware of and what you're not. But please follow the links on this page as a starting point then get back to us with detailed questions. It's an electrolytic filtering process, not just an ordinary filtering process. Good luck.

Regards,