Application of Pearson’s principle to interpretation of the duration of the residual protective effect of organic inhibitors as a function of the nature of a metal and anion

Residual inhibition coefficients K t of acidic corrosion by a mixture of an organic inhibitor and an anionic additive for Al, Zn, Fe, and Ni decrease linearly in time; the duration of the residual protective effect depends linearly on the logarithm of the anionic additive concentration in the preadsorption solution. The effect of anions on the values of K t and τ for the studied mixtures is determined by the nature of the metal and anion. It is established on the basis of Pearson’s principle of hard and soft acids that the K t and τ values grow upon an increase in the organic inhibitor concentration in preadsorption solutions, irrespective of the nature of the metal.