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Unexpected copper plating effects

Hi,

Out of curiosity, I set up a basic copper plating arrangement, 200g copper sulphate ⇦ this on eBay or Amazon [affil links] (root killer), 30 ml sulfuric (acid drain cleaner ⇦ this on eBay or Amazon [affil links] ), and .1g salt all mixed with deionized water to make 1 liter. I also added 1/2 ml of glycerine (polyethylene glycol I believe) thinking that this might work as brightener. The anode was copper pipe. It worked pretty well for my simple purposes, but I noticed a couple of unexpected things that I hoped others might be able to shed light on.

1) the copper pipe anode turned dark brown after operation, whereas I expected it to turn a bright copper color as it dissolved. Any idea why?

2) a loose white film formed on the anode (over the brown copper) Any idea what it might be?

3) I did most plating at a voltage under 1/2 volt, but when I tried more I got a lot of loose grains forming. In the most extreme case, I dipped an inch or so of wire in as cathode and passed a couple of amps through. in minutes it formed a pencil thick coating that was loosely attached with color ranging from black to deep rust to copper color. The coating easily came off as a loose granular paste. I presume it is mostly copper crystals (though it did not look like clean bright copper). Any idea what this is?

Thanks for any thoughts.

Eric Slighton
hobbyist - San Francisco, California
2004

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You need to have more similar areas for the anode and cathode. It sounds as if the current density on the copper anode was too low, resulting in poor dissolution of the copper and the anode was too high, resulting in "burning". When the cathodic current is too high, you can get poor adhesion. Ideally you should also make sure the cathode is chemically clean; to do this you should give it a good scrub with chalk, followed by a dip in 10% caustic soda ⇦liquid caustic soda in bulk on Amazon [affil link] solution and then a two minte dip in 10% sulfuric acid. Good rinsing is essential. As a general guide, copper should be plated at about 25-40A/ft2.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2004