Comparison of inhibition performance of thiadiazole derivatives containing sulfhydryl groups: Experimental and theoretical calculations

Corrosion inhibitors could significantly reduce the corrosion effect of seawater on carbon steels, which were widely used in seawater cooling systems and seawater desalination systems. The corrosion inhibition properties of 1,3,4-thiediazole (TD) and 2-mercapto-1,3,4-thiadiazole (MTD) and their relationship with molecular structures were systematically studied by experimental and theoretical methods. TD and MTD were composite corrosion inhibitors with the higher proportion of cathodic corrosion inhibition, and their corrosion inhibition was based on the enlarged resistance of the electrochemical dissolution reaction of the iron. Their coverage on the surface of carbon steel and the negative movement of the potential they caused would promote each other and formed the stable adsorption. The mercaptol extended the distribution range of the negative electrostatic potential of MTD, reduced the spatial steric resistance of coordination and the energy gap of the frontier molecular orbitals, and raised the number of coordination transfer electrons, which made MTD exhibited superior corrosion inhibition performance than TD. The adsorption behavior of MTD was in line with the characteristics of Langmuir adsorption and was the combination of physical adsorption and chemical adsorption. Its adsorption form was laminated adsorption, and it was conducive to the formation of feedback bonds, which led to high stability of adsorption.