The effect of steel modifying with zinc oxyethylidenediphosphonate on its passivation in solutions of certain inhibitors

Abstract

It is shown that a solution of zinc complex of 1-hydroxyethane-1,1-diphosphonic acid can be used for modifying the surface of low-carbon steel in order to enhance its passivation by aqueous solutions of other inhibitors (1,2,3-benzotriazole, sodium alkylcarboxylate, and their mixture). The results of accelerated tests of protectability of nanosized passivating coatings are compared. To assess the efficiency of steel protection by electrochemical tests, the difference in pit formation potentials ΔE = E ⁱⁿ_pt − E ^sup_pt are determined from polarization curves in borate buffer solutions containing NaCl in the absence (E ^sup_pt ) and in the presence (E ⁱⁿ_pt ) of the inhibitor. The direct corrosion tests are carried out in cells and in the G-4 humidity chamber (GOST (State Standard) 9.054–75) where the time of the appearance of first indications of corrosion on samples τ_cor serves as the criterion of efficient protection. Three groups of coatings can be distinguished: with weak protectability characterized by ΔE < 0.20 V and τ_cor < 6.25 days; with medium protectability and ΔE = 0.20–0.40 V with τ_cor reaching 9 days; and the with high protecting efficiency and ΔE > 0.40 V where τ_cor can be even longer than 25 days.