Abstract Green Corrosion
The Heating, Ventilating and Air Conditioning Contractor (HVAC) have been experiencing serious issues associated with the leaks in the copper tube heat exchange coils. Usually these leaks are small but numerous in numbers and most of them are located in the single coil. Several reasons have been accrued to coil leaks. It also includes chlorides from pool chemicals and clothes washing sulphur from tap water, lubricants and nearby industries, and ammonia compounds from cleaners or nearby industries.
The "green rusts” ("fougerite") is an unbalanced iron compound. The rust is formed as the result of copper corrosion. These "green rusts” have the divalent (FeII) and trivalent (FeIII) iron. The composition of “green rust” formed due to chloride is [FeII3 FeIII (OH)8]+ [Cl. H2 O]-. This type of rust is stable when pH is about 7 or 9. Copper turn green after exposure to the atmosphere as the result of reaction with Oxygen. The reaction occurs when water, moisture condensation or rain (having dissolved oxygen)comes in contact with the copper. It is significant to find that when copper exposed to atmosphere its color automatically gets change to dark brown first and then blue after several years. The principle of rusting is same as that of the iron rusting.
Green Corrosion Removal
Ammonia (the solution in water, not gas!) is the best solution available as it forms the soluble, intense blue tetraminecopper(II) complex - [Cu(NH3)4]2+