Dennis Miles via EV wrote:
Bill, You are right copper oxide is a "Semi-conductor," and it was used in battery chargers 100 years ago, as rectifiers. But whereas I was a bit strong in calling it an insulator, As it passes current in only one direction, I would not call it a very good conductor either. In my experience only gold does not oxidize. However, gold is expensive.
As usual, it's a complicated subject that doesn't lend itself to oversimplification. But I'll try... :-)
Gold doesn't oxidize at all. That's why it's used for important electrical connections where you don't want any corrosion or oxides to add resistance.
Copper oxide is sort-of-a-conductor (a semi-conductor). You can make diodes with it ("crystal radio" detectors, solar cells, rectifiers for meters or battery charger). As far as EVs are concerned, copper oxide is fragile and easily rubbed or scraped off, and does not quickly form again on a surface. Thus, you can bolt two copper buss bars together and get a good connection despite a little copper oxide in the way.
Silver oxide is much like copper oxide. It doesn't conduct, but scrubs off very easily when connectors are mated. Cheaper than gold, better than copper.
Tin oxide has a lot of these same properties, and forms a lot slower than copper oxide. It's also a lot cheaper than gold or silver. Most bare copper is tin plated for electrical connections because the tin oxide surface is even less trouble for making good connections. Tin oxide is a poor conductor, but gets broken or scrubbed off when you bolt or plug tin plated connections together.
Zinc oxide is good at this, too. Worthless as an electrical conductor; but excellent at protecting the underlyling metal from corrosion. Zinc coating are called "galvanized".
Aluminum oxide is a "whole 'nother thing". It forms almost instantly, is a very good insulator, and is very hard to remove (they make sandpaper out of it). It's worth going to great pains to keep it out of your connections.
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