INHIBITION-MECHANISM OF SODIUM 3-NORMAL-OCTYLMERCAPTOPROPIONATE FOR IRON CORROSION IN 0.5M NACL SOLUTION

The inhibition mechanism of sodium 3-n-octylmercaptopropionate for iron corrosion in an aerated 0.5 M NaCl solution was investigated by polarization and impedance measurements. More than 80% of the inhibition efficiency was obtained at an inhibitor concentration of 1 x 10(-3) M over the period of 72 h. The x-ray photoelectron spectra showed that the iron surface inhibited with this compound was covered with a layer of ferric and ferrous oxides containing NaCl and a slight amount of the inhibitor. Electron probe microanalysis (EPMA) studies indicated that local corrosion occurred on the iron surface and that the inhibitor and Cl- were concentrated at pits on the surface. It was supposed that this inhibitor suppressed the pit formation by coverage of a reaction product with Fe3+ and the anodic dissolution of iron in the pit by chemisorption of the inhibitor via an oxygen or sulfur atom.