Abstract
“Ant-nest” corrosion is a specific type of premature failure of copper tubes used in air-conditioning units causing the loss of refrigerant liquid and consequent environmental pollution. It is known that attack requires the simultaneous presence of moisture, oxygen, and a corrodent, usually formic acid. This type of corrosion occurs in thin-walled copper pipes, especially when copper is deoxidized high residual phosphorus. A study has been made of the copper corrosion products formed by the action of formic acid vapor for exposure at 100% relative humidity and under thermal cycling. The corrosion-product layer was characterized using X-ray diffraction (XRD). The identified compounds were cuprite , copper hydroxide hydrate , copper hydroxyformate [Cu(OH)(HCOO)], anhydrous copper formate , copper formate dihydrate , and copper formate tetrahydrate . Tentatively, the latter phase is described in relation with ant-nest corrosion in this paper. A kinetic study of the solid crystalline phases formed on copper has been performed using XRD patterns and the compound ratio has been compared over exposure time.
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