Copper corrosion inhibition in O 2-saturated H 2SO 4 solutions

Abstract

Corrosion inhibition of copper in O 2-saturated 0.50 M H 2SO 4 solutions by four selected amino acids, namely glycine (Gly), alanine (Ala), valine (Val), or tyrosine (Tyr), was studied using Tafel polarization, linear polarization, impedance, and electrochemical frequency modulation (EFM) at 30 °C. Protection efficiencies of almost 98% and 91% were obtained with 50 mM Tyr and Gly, respectively. On the other hand, Ala and Val reached only about 75%. Corrosion rates determined by the Tafel extrapolation method were in good agreement with those obtained by EFM and an independent chemical (i.e., non-electrochemical) method. The chemical method of confirmation of the corrosion rates involved determination of the dissolved Cu 2+, using ICP-AES (inductively coupled plasma atomic emission spectrometry) method of chemical analysis. Nyquist plots exhibited a high frequency depressed semicircle followed by a straight line portion (Warburg diffusion tail) in the low-frequency region. The impedance data were interpreted according to two suitable equivalent circuits. The kinetics of dissolved O 2 reduction and hydrogen evolution reactions on copper surface were also studied in O 2-saturated 0.50 M H 2SO 4 solutions using polarization measurements combined with the rotating disc electrode (RDE). The Koutecky–Levich plot indicated that the dissolved O 2 reduction at the copper electrode was an apparent 4-electron process.