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The corrosion of a copper electrode in a 5% HCl solution is analyzed using impedance data recorded at the corrosion potential. A straight line is observed at high frequencies, attributed to a diffusion process in the film covering the copper surface. This line curls down towards the real axis at intermediate frequencies, drawing a depressed quarter lemmiscate. The impedance plot is completed by a second straight line at very low frequencies.

The copper corrosion products originated by the action of formic, acetic and propionic acid vapors at a 100% relative humidity were studied for a period of 21 days. Five formic, acetic and propionic vapor concentrations (10, 50, 100, 200 and 300 ppm) were tested. The corrosion-product layers were characterized using electrochemical methods. Some of the compounds identified were: cuprite (Cu2O), for the three acids; cupric hydroxide monohydrate (Cu(OH)2*H2O) and copper formate tetrahydrate (Cu(HCOO)2*4H2O), for formic acid; copper acetate dihydrate (Cu(CH3COO)2*2H2O) and copper hydroxide acetate dihydrate (Cu4(OH)(CH3COO)7*2H2O), for acetic acid; and copper propionate (Cu4(OH)(CH3CH2COO)7*2H2O) for propionic acid.