Inhibition of copper corrosion by isatin in aerated 0.5 M H2SO4

The corrosion inhibition of commercial copper by means of isatin was studied in aerated 0.5 M H₂SO₄ in the temperature range 25-55 °C using weight-loss, potentiodynamic and spectrophotometric tests, and determination of double layer capacitance. Inhibition efficiencies up to 94% in the concentration range of 1×10⁻⁴-7.5×10⁻³ M of isatin were obtained. The corrosion rates estimated with weight-loss measurements were higher than those correspondingly determined with the potentiodynamic test, especially at higher concentrations of inhibitor. This is in accord with other researches that have pointed out the limitation of the Tafel line extrapolation method in the determination of corrosion rates. The kinetics of cuprous and cupric ion formation and UV-visible spectra support the formation hypothesis of a complex between copper and isatin. The adsorptive behaviour of isatin on copper 0.5 M H₂SO₄ was also investigated.