Corrosion inhibition of copper in aerated 0.5 M sulfuric acid by indole-2-carboxylic acid

The inhibiting action of indole-2-carboxylic acid (C9H7NO2) on the corrosion of commercial copper in aerated 0.5 M sulfuric acid (H2SO4) has been investigated in the temperature range from 25 degrees C to 55 degrees C by weight loss, potentiodynamic and analytical tests, and the determination of double-layer capacitance. The results have revealed a good inhibitor efficiency, up to 98% in the concentration rangefrom 1 x 10(-4) M to 4 x 10(-3) M. Indole-2-carboxylic acid has been found to act as a mixed inhibitor. The kinetics of Cu+ and Cu2+ formation that followed in 72 h of gravimetric testing shows that indole-2-carboxylic acid probably affects the corrosion reaction mechanism through complexes with cuprous ions. The corrosion rates determined through weight-loss measurements are much higher than those obtained with potentiodynamic tests. This is in accord with other researchers who have found limitations to the extrapolation of polarization curves (and to the theory of mixed potentials) in the determination of corrosion rates. The adsorptive behavior of indole-2-carboxylic acid also has been investigated in a wide potential range (-900 mV to 200 mV with regard to corrosion potential [E-corr]).