Dual-purpose pyrazine-based corrosion inhibitor for acid cleaning of carbon steel and nickel resist in 1 M HCl at 60 °C

Two of the challenges facing the effective application of organic corrosion inhibitor systems for practical industrial acid cleaning are the elevated temperature of operation (up to 60 o C) and the need to simultaneously protect a variety of metallic equipment during a single operation. An inhibitor system that delivers high efficiency under these conditions will save huge revenue and time for many industries and boost the scientific literature. We present a pyrazine dicarboxylic acid + KI inhibitor system capable of simultaneously protecting carbon steel and nickel resist with > 80 % and > 90 %, respectively, during acid cleaning in 1 M HCl at 60 oC. Electrochemical impedance spectroscopy and potentiodynamic polarization agreed with weight loss measurements that the inhibition mechanism is slightly cathodic on carbon steel but anodic on nickel resist. Scanning electron microscopy characterization showed that inhibitor system minimized grain boundary attack that leads to surface microstructural destruction of both alloys. Density functional theory and Monte Carlo simulations confirmed that the nitrogen atoms in the pyrazine moiety, and the oxygen atoms in the carboxylate group, create the linkages between the inhibitor system and the substrates, whereby nickel atoms in nickel resist boost substrate-inhibitor interaction. The ability for these centers to become protonated in the acid solution further enhanced the inhibition efficiency in the presence of iodide anions.