CS<inf>2</inf> mediated synthesis of corrosion-inhibiting mercaptobenzothiazole molecule for industrial zinc: Experimental studies and molecular dynamic simulations

Abstract

In this study, 2-mercaptobenzothiazole (MBT) was synthesized from a CS2 mediated formation scheme involving a catalyzed reaction between aminophenyl disulfide with metal sulfide under N2 atmosphere. The formation mechanism of MBT involved the development of a C–S bond under relatively less reaction time and milder thermal conditions, as an alternative route to organic thiols. The tendency of MBT toward Zn-surface adsorption and corrosion inhibition was investigated in chloride-enriched (1 M HCl) acidizing solution. MBT acted as a corrosion inhibitor within this acid medium and this was consistent with molecular adsorption and formation of mercaptobenzothiazole films on Zn substrate. Corrosion investigations were performed using electrochemical impedance spectroscopy and Tafel polarization techniques. Surface analytical techniques, e.g. Scanning Electron Microscopy, Atomic Force Microscopy and X-ray Photoelectron Spectroscopy, were also utilized to probe metal-surface changes as well as adhering corrosion inhibiting MBT films on Zn substrates. Inhibition of Zn corrosion increased with MBT concentration due to formation of passive MBT protective films on the metallic surface; this was consistent with increase in charge transfer resistance (Rct) and reduced magnitudes of corrosion current density (jcorr). Magnitude of Rct up to 156.8, 225.8, 420.7 and 753.5 Ω cm2 were recorded for 0, 100, 300 and 500 ppm MBT while the trend of jcorr reduced in the order: 500 ppm (89 μA cm−2) < 300 ppm (230 μA cm−2) < 100 ppm (340 μA cm−2) < 0 ppm (955 μA cm−2) MBT. The MBT heterocyclic molecular structure may have been the greater edge toward Zn surface adsorption, hence corrosion inhibition. The extent of interfacial interactions between MBT and the Zn layer has also been theoretically investigated by molecular dynamic simulations. Zn corrosion resulted in chloride-induced pits with a predominantly anodic kinetics. Since molecular structure is an important aspect of sustainable corrosion inhibition design, the present study reflects a modern design for alleviating corrosion in industrial metallic Zn.