Investigation of the Inhibiting Effect of Cerium Ions on the CorrosionBehavior of OC404 Stainless Steel in Sulfuric Acid Medium

The inhibiting effect of Ce ions, introduced in the form of Ce(SO4)2, on the corrosion electrochemical behavior of stainless steel OC404, has been studied in sulfuric acid corrosion medium (0.05 M H2SO4). On the basis of the obtained data on the values of the density of the corrosion current (icorr), evaluated using the dependences E-lgi, both in inhibited and uninhibited corrosion medium, the degree of corrosion protection in the presence of the inhibitor was calculated, as well as the fraction of surface coverage (Q) the electrode surface with inhibitor. These studies were carried out with samples of non-treated thermally steel (SS) and thermally treated steel (SSt.t.). The cathodic reaction of reduction of the oxidative component of the medium Ce was found to be the basic driving force of the conjugated anodic process, leading to a transition of SSt.t. from active into passive state. Thereupon an option is created to form an efficient protective film of phase type on the SSt.t. surface reaching a degree of inhibition efficiency of about 98 %. In order to elucidate the nature of the inhibiting action of cerium ions the influence of the value of the equilibrium oxidation-reduction potential of the Ce/Ce ion pair was investigated as well as that of the exchange current of the oxidation-reduction process upon the processes of passivation of the studied steel. The obtained results give the reason to classify the cerium ions as cathode type of inhibitor having oxidative action.

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