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I wrote:
Maybe I can get a swatch or one of you can do the test (eletromotive potential) and let us know how it comes out.
Well I was at the airport today and got a swatch of carbon cloth from Hal Woodruff. Thanks, Hal. I just finished the test.
I took a cup of filtered tap water and bubbled my breath through it to add CO2 to add carbonic acid just as the atmosphere does. It can also be salty near the sea from sea spray and fog, and it can have nitric acid from NO2 automotive emissions and lightning nitrogen fixation. Be that as it may, I settled mostly for CO2. With about 1 square inch of carbon cloth in the water and about 1 inch of silver wire close to the cloth I measured:
C + 0.025 V – Ag
With 1 inch of copper wire I measured:
C + 0.250 V – Cu
So it would appear that carbon/silver is probably not too much of a problem from a corrosion standpoint and as Shannon just said, the Electrodag coating is between epoxy and paint, so probably not that much contact with the carbon. As Emily Latella said, “Never Mind.”
So that still leaves open the question about the direct environmental impact such as SO2 and direct corrosion between the silver and copper components of the Electrodag coating itself. That electromotive couple is in the ¼ volt region, certainly non-trivial. Electrodag should be able to tell you how well this stuff will hold up in a wet atmosphere. The key here is how well the copper is covered. If copper and silver are simultaneously exposed to moisture, corrosion can be significant. Remember fog, rain, morning dew, etc. If Electrodag can’t answer the question, get a small sample and coat a test coupon, maybe a couple of inches square, complete with paint and a couple of brass bolted on connections about an inch apart, such as an antenna connector ground plane might have. After construction measure the resistance between the bolts – it should be in the ¼ ohm region. Leave outdoors in the weather for a month or so, especially so it gets watered with the lawn and exposed to the sun. Measure again and inspect carefully. Let us know how it came out. I certainly would be interested.
Chas.
LNC2 360JM
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