Kinetic properties of the passive film on copper in the presence of sulfate-reducing bacteria

Copper specimens were exposed to Sulfate-Reducing Bacteria (SRB) for 10 months under the conditions corresponding to the final disposal of high-level nuclear waste. In-situ electrochemical impedance spectroscopy (EIS) measurements were carried out to characterize the surface-environment interface after various times of exposure. The EIS results are interpreted in terms of the Point Defect Model (PDM), in order to obtain kinetic information on the formation of the Cu₂S passive film. The standard rate constant and the rate constants for the surface reactions revealed that the Cu₂S layer is a p-type semiconductor. The diffusion constant for cation vacancies in the barrier layer and the average bulk cation vacancy concentration in the barrier layer were found to be on the orders of 10−¹³ cm²·s⁻¹ and 10²² cm⁻³, respectively, i.e., both slightly higher than reported in literature for corresponding electrochemically developed Cu₂S layers. The electric field strength was approximately 3·10⁵ Vcm−¹ at all measurement points. These results are presented and discussed in this work in the light of storage of high-level nuclear waste.