Using Indole to Inhibit Copper Corrosion in Aerated 0.5 M Sulfuric Acid

Inhibition of copper corrosion in aerated 0.5 M sulfuric acid (H₂SO₄) solutions containing various concentrations of indole was studied in the temperature range from 25°C to 55°C using potentiodynamic curve, weight-loss, and analytical methods. Indole shifted corrosion potentials toward more noble values (i.e., it had a stronger influence on the copper dissolution reaction than on the cathodic oxygen reduction). Indole probably affected the corrosion reaction mechanism through complexes with cuprous ions. At 25°C, 35°C, and 45°C, the adsorption behavior of indole followed Frumkin’s isotherm. At 55°C, it followed that of Langmuir. The standard free energies of adsorption (ΔG°_(ads)) were –21.6 kJ/mol, –18.3 kJ/mol, –22.1 kJ/mol, and –27.9 kJ/mol, respectively.