Electrochemistry of corrosion mitigation of brasses by azoles in basic medium

The article describes the corrosion inhibition effects of four metal cations (Al, Sn, Pb, Mn) as dopants and five azoles as outer protective layers on pure copper and four brass alloys in borate buffer at pH 10.4. The electrochemical behavior of the four doped brasses, i.e., CuZnAl, CuZnSn, CuZnPb and CuZnMn was investigated using cyclic voltammetry (CV), potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy. The corrosion rate (CR) of all the brasses was found slower than that of pure Cu (0.132 mm year(-1)) due to the presence of dopant ions, i.e., CuZnMn had the highest CR, 0.019 mm year(-1) and CuZnAl had the lowest 0.009 mm year(-1). Five azoles, namely benzotriazole, mercaptobenzothiazole (MBT), benzimidazole, mercaptobenzimidazole and thiadiazole, were successfully employed as efficient corrosion retarders for the brasses. Their concentration-dependent corrosion inhibition was attributed to the spontaneous chemisorption on alloy surface following Langmuir isotherm pattern. Among all the inhibitors, MBT showed maximum corrosion inhibition efficiency between 91 and 96% for different brasses. The impedance modulus markedly increased with inhibitor concentration, revealing a protective effect of these corrosion inhibitors and thus complementing the CV and PDP results.