Whether it’s your smartphone, tablet, laptop, desktop PC, car, boat or even an aeroplane, everywhere with a DC voltage (component), there is corrosion. Brown, black, red, orange, yellow, green and blue buildups around electrical connections. Such as in the picture on the left; the inside of a connection box of an electric motor.
It’s not copper oxide. Copper oxide is brown and form as a patina on the surface of a copperous material. It’s a chemical reaction between the oxygen O2 molecule in the Ri with the copper molecule Cu forming copper(I)oxide.
Instead it is a complex chemical reaction between the copper, oxygen, water, acids, chlorides and salts in the air, with a DC voltage component driving the reaction. The higher this DC voltage component, the faster the reaction takes place. An AC voltage can also contain a DC voltage component, and a chance of galvanic corrosion remains. The chemical reaction turns the copper into various coppersalts. There copper-salts are converted into hydrates and form crystals. The color of these crystals depend on the electron charge which is determined by the chemical makeup percentages of, among many others copper(II)sulfate (pentahydrate), copper(II)hydroxide and copper(II)chloride.
Next time, remove your cell phone battery when you’re out in the rain or have been sweating with your phone in your inside pocket. Had an accident with a cup of coffee and your laptop, remove the battery. Just let liquids drip out and let the rest dry-up in a warm location. When needed, open up your device to remove trapped water under shields and remove sugar et cetera. Or hand over your device with disconnected battery to a local repair shop.
Or in our case, the person who installed the motor should have used dielectric grease on the connection to remove water and damp air from the DC voltage potential.