Effect of Divalent Cations in Langmuir-Blodgett Films on the Protection of Copper against Corrosion

Abstract

Langmuir-Blodgett films (LB) of hydroxamic amphiphiles were used as coating barriers on metal surface against corrosion. Two long-chain hydroxamic acids [CH3(CH2)16CONHOH] monolayers in the presence of some divalent cations (Ca2+, Mg2+, and Cu2+) have been studied at different pH of the subphase. The monolayer was characterized by surface pressure-area isotherms and visualized by Brewster angle microscope (BAM). Compact Langmuir layers were deposited on copper surface, where the modified surfaces were characterized by contact angle measurement as well as by electrochemical techniques. The morphology of LB coated copper surface was visualized by atomic force microscopy (AFM). The coated copper surfaces were tested in corrosive media at acidic and neutral pH. The results show that the multi-molecular LB films of hydroxamic acid salts form good barriers against copper corrosion. The comparison of these results with copper coated by LB layers without divalent cations shows that the presence of divalent cations in the subphase increases the copper corrosion inhibition. The octadecanoyl hydroxamic acid (C18N) results in better and more stable monolayer with cations in the subphase.