A comparative study on copper corrosion originated by formic and acetic acid vapours

The copper corrosion rate and products originated by the action of formic and acetic acid vapours at a 100% relative humidity were studied. Copper specimens were exposed to formic and acetic acid vapours for a period of 21 days. Five formic and acetic acid vapour concentrations (10, 50, 100, 200 and 300 ppm) were tested. Copper corrosion rates of up to 1300 mg m−2 d−1 (mmd) for formic acid and up to 2300 mmd for acetic acid were measured using a gravimetric method. The corrosion-product layers were characterised using electrochemical, X-ray powder diffraction and scanning electron microscopy techniques. Some of the compounds identified were: cuprite (Cu2O), for both acids; cupric hydroxide monohydrate (Cu(OH)2 ·H2O) and copper formate tetrahydrate (Cu(HCOO)2 · 4H2O), for formic acid; and copper acetate dihydrate (Cu(CH3COO)2 · 2H2O) and copper hydroxide acetate dihydrate (Cu4(OH)(CH3COO)7 · 2H2O), for acetic acid.