A contribution to the understanding of the synergistic effect of anions for the corrosion inhibition of Fe by amines

Abstract

Synergistic and antagonistic effects of organic or inorganic anions with alkyl or cyclic amines were observed in the corrosion inhibition of Fe in HClO 4. Anions specifically adsorbed on Fe attract amine cations electrostatically into the Helmholtz electrical double layer. If the electron availability of the amines is insufficient, the cationic amines simply cover the anion layer rather than chemisorb directly on the Fe surface. In the case of weak anion adsorption, however, the cations often tend to withdraw the adsorbed anions into the HClO 4. Synergistic adsorption is, therefore, classified into two types plus a mixture of the two : (1) specific co-adsorption of anions and amines, as reported in a previous paper 5; and (2) ionic or physical overlap adsorption of amine cations over the anion-covered Fe surface. In the latter case, increase of amine concentration may cause withdrawal of the anions from the Fe surface into the solution. The surface coverage thus decreases and, as a result, an antagonistic effect should be observed.