Adsorption from Neutral Solutions of Sodium Alkyl Phosphonates on Zinc and Its Passivation

Ellipsometry is used to study the adsorption of the sodium salt of decyl phosphonic acid (SDP) on zinc in a borate buffer solution with pH 7.4. It is found that adsorption of SDP is described by the Tyomkin equation on both oxidized and reduced zinc surfaces, and its adsorption activity on the reduced surface is higher. The inhibiting effect the sodium salt of dodecyl phosphonic acid (SDDP) has on zinc is studied in a chloride-containing borate buffer solution with pH 7.4. It is shown that SDDP has better passivating ability than SDP. The passivating effect of SDDP depends on a certain threshold concentration of the inhibitor. Increasing the alkyl phosphonate concentration and the duration of electrode conditioning in the solution enhances the protective properties of films formed when it is present on zinc.