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Corrosion rate |
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Run off |
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adherent |
Basic copper salts
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Copper carbonates |
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Copper oxides |
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Because of the increase in thickness of the outer oxide layers (patina protective layer), there is a continuous reduction in the effects of the atmosphere, so that the formation of oxides caused by the oxidation of metallic copper gradually becomes slower. Rain, snow, wind and air constituents have a slow weathering effect on the oxide layers. However, this loss is constantly balanced out by the formation of new oxides.
The corrosion rate is made up of two parts: the adherent and the weathered basic copper salts, copper carbonates and copper oxides (patina). Therefore, the corrosion rate cannot be used to assess the input of copper into the environment. It only serves to calculate the useful life of metal roofing.
Improvements in the air quality – in the last 20 years the concentration of sulphur dioxide in the atmosphere has dropped by a factor of 4 – lead to a considerably lower rate of corrosion than stated in less up-to-date literature.
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