Inhibition by CO of the corrosion of Fe, Ni, and their alloys in concentrated HCl solutions

Inhibition by CO of the corrosion of Fe, Ni, and three alloys, containing either Fe and large amounts of Ni (Incoloy 825) or large amounts of Fe (Uniloy-420 and N80 steels) in solutions containing between 7.5% and 28% HCl was studied using potentiodynamic polarization curves, gravimetric tests, and FTIRS. In all cases, but Uniloy-420 in 28% HCl, a clear inhibition of corrosion in the presence of CO in the solution was shown by the gravimetric tests and from cyclic voltammetry, the inhibition being higher in the case of Ni and Ni-containing alloys. CO chemisorbed on Fe and/or Ni atoms present on the alloy surface was identified as the species responsible for corrosion inhibition. The inhibition of corrosion is higher in the cases of Ni and Incoloy 825.

► CO adsorbs on Fe, Ni and Fe- and Ni-containing alloys even in concentrated HCl solutions.
► Adsorption of CO on the surface of these materials has an inhibiting effect on their corrosion.
► The inhibition of corrosion is higher in the case of Ni or Ni-containing alloys.