Temporal Aspects of Corrosion Inhibition on Copper, Silver, and Copper-Silver Alloys: an Electrochemical Impedance Spectroscopy Study

Electrochemical impedance spectroscopy (EIS) was utilized to delve into the corrosion inhibition of eutectic Cu-Ag alloy and its components (Cu and Ag) in an aqueous, aerated 0.1 M KNO3 solution. This alloy plays a major role in the water cooling of central processing units in data storage centers. Two organic inhibitors, namely, 1,2,3-benzotriazole (BTA) and 2,5-dimercapto-1,3,4-thiadiazole (DMTD), were utilized in this study. The corrosion inhibition slowly evolved over time as diagnosed by an increase in the charge transfer impedance and the gradual tendency of the Nyquist profiles to arc toward the real axis. This trend was attributed to the gradual formation of organometallic passivation layers. The EIS data underlined the specific affinity of BTA and DMTD toward the Cu and Ag surfaces, respectively. A transition of the double-layer equivalent circuit element from ideal capacitance to a constant phase element was observed for the alloy compared to the pure metals. This was attributed to the heterogeneity induced by Cu-rich and Ag-rich phases in the alloy and by the formed oxides/protective film on the alloy surface. The EIS study demonstrated that both BTA and DMTD can provide sufficient corrosion inhibition to Cu-60Ag alloy with DMTD being significantly more effective.