Copper "Trees" on Aluminum
This is an example of copper trees growing on a small particle of aluminum foil in an oil filled large transformer
bushing. Electromotive substitution can occur where ever metal ions are mobile.
Transmitted Crossed Circular Polarized Light and Darkfield Reflected Light Illumination
Copper trees will grow on a small fragment of aluminum in bushing oil when copper is taken into solution in the oil.
Copper will plate the aluminum if only very low levels of copper are present.
Significance in the Environment:
This indicates that the oil is corrosive to copper and that some of the copper compounds formed are soluble in the oil.
The reddish color of the copper stands out in sharp contrast to the white of the aluminum. Even in low concentrations the copper plating out
on the aluminum will be easily visible.