Thioamide Compounds as Corrosion Inhibitors for Stainless Steel in H2SO4 Solution

The influence of organic compounds on the corrosion of stainless steel in 0.5 M sulfuric acid (H2SO4) was investigated using weight-loss and potentiodynamic polarization techniques, as well as open-cirucuit potential (OCP) measurements. The nature of the film formed and the adsorption mechanism, as well as thermochemical parameters involved, were explored and expounded. This investigation indicated that the inhibition efficiency increases with increasing the concentration of organic compounds. The inhibitors are of the mixed type but dominantly act as anodic in 0.5 M H2SO4. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to characterize the surface and examine the morphology of the Type 304 (UNS S30400) stainless steel under ordinary acid attack with that formed under inhibited conditions. The adsorption of the inhibitors was expressed reasonably by the Langmuir adsorption isotherm. The calculated activation energy and thermodynamic parameters point to a mixed adsorption pattern of inhibitor molecules, with physical adsorption as the dominant mode.