Employing electrochemical frequency modulation for studying corrosion and corrosion inhibition of copper in sodium chloride solutions

The inhibition effect of 2-carboxymethylthio-4-(p-methoxyphenyl)-6-oxo-1,6-dihy-dropyrimidine-5-carbonitrile (CPD) towards the corrosion of copper was studied in aerated stagnant 3.5% NaCl at 25 °C using ac techniques include electrochemical frequency modulation and electrochemical impedance spectroscopy as well as potentiodynamic polarization measurements. Corrosion rates determined using electrochemical frequency modulation (EFM) which measures the non-linear behaviour of a corroding system are compared with corrosion rates obtained from traditional electrochemical techniques and show good agreement. Data obtained from EIS were analyzed to model the corrosion inhibition process through equivalent circuit. Polarization measurements showed that CPD acts as mixed-type inhibitor. The inhibition efficiency increases with an increase in the concentration of CPD. The adsorption of the inhibitor on the copper surface in the sodium chloride solution was found to obey Langmuir’s adsorption isotherm. A mixed inhibition mechanism is proposed for the inhibitive effects of CPD as revealed by potentiodynamic polarization technique.