טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentHayon Joseph
SubjectStudy of Copper Corrosion Processes in Surfactants
Solutions
DepartmentDepartment of Chemistry
Supervisors Professor Emeritus Chaim Yarnitzky (Deceased)
Professor Emeritus Joseph Yahalom


Abstract

The behavior of copper was studied in aqueous borate solution in the presence of surfactant sodium dodecylsulfate (SDS), and sodium dodecylbenzenesulfonate (SDBS) using DC and AC electrochemical techniques as well as surface analysis techniques. It was found that at pH 7 in the absence of surfactants, passivity occurs through the formation of a duplex Cu2O/CuO/Cu(OH)2 structure. However, in the presence of SDS, the results indicate passivity breakdown and severe pitting to the copper surface. The pitting potential (Ep) in the presence of SDS varies with the dodecylsulfate ions (DS-) concentration: Ep= -0.123log[DS]-0.268. The passivity breakdown is attributed to formation of the Cu(DS)2 complex which has also been detected by reflectance Fourier transform infrared spectroscopy.

Electrochemical impedance spectroscopy results show that migration of copper ions within the oxide film to the oxide surface proceeds more readily in the presence of DS- at the potential where passivity breakdown starts to occurs (0.050 V vs. SCE). At pH 7.5 where stable Cu2O oxide is possible no passivity breakdown is observed due to oxidation of Cu2O to CuO rather than to Cu2+. The Pourbaix diagram for copper / SDS is used to explain the different behavior of copper corrosion versus pH.

As opposed to the effect of SDS on the behavior of copper the presence of SDBS at the same conditions contributes to stabilization of the Cu2O oxide film. Cyclic voltammogram, (CV) curves in aqueous solutions show that DBS- ions stabilize Cu+ in a manner to a known corrosion inhibitor Benzotriazole, (BTA).  The inhibition efficiency of SDBS increases with the DBS- ions concentration in the solution up to 70% at 0.5 mM SDBS. Adsorption of DBS- ions on the copper surface obeys the Langmuir adsorption isotherm model, the equilibrium constant was determined to be 3.08*104 M-1. A stable and an arranged barrier film of DBS molecules is formed on the copper surface as was characterized by Fourier transform infrared reflection absorption spectroscopy, (FT-IRAS).