Abstract
The effects of pH and chloride concentration on the electrochemical corrosion of copper in aqueous sodium chloride (NaCl) media were studied at the micro scale using a microcapillary droplet cell and at the macro scale using a conventional large scale cell. Using an experimental design strategy, electrochemical response surface models of copper versus pH and NaCl concentration were constructed with the minimum number of experiments required. Results show that the electrochemical behavior of copper under corrosive media shows significant differences between the micro and macro scale experiments. At the micro scale, the pit initiation of copper occurs at more negative potentials for high NaCl concentrations and alkaline pH values. Also, the micro scale potentiostatic measurements indicate higher stabilised passive currents at high NaCl concentrations and low (acidic) pH values. At the macro scale, the pH is shown to have a greater influence on the corrosion potential. The chloride concentration is the most significant factor in the passive current case while at the micro scale the effect of these two factors on the passive current was found to be the same. The surface morphology of the formed patina on the corroded copper in both micro and macro systems reveal a more significant role of the chloride concentration on the structure and the grain size of the patinas. Finally, micro and macro electrochemical impedance spectroscopy of copper at various NaCl concentrations and pH values demonstrates a different behavior of copper after several potentiodynamic polarization cycles.
Highlights
It is known that the corrosion mechanism of copper is strongly dependent on the presence of chloride ions
This study investigates the electrochemical corrosion of copper in macro and micro systems in various NaCl solutions
An experimental design strategy known as central composite design (CCD) was implemented to minimize the number of experiments required, and determine which variable has the greater influence on the corrosion of copper
Summary
It is known that the corrosion mechanism of copper is strongly dependent on the presence of chloride ions. Probe electrochemical techniques, using microcapillary cells or micro-electrodes, show key differences compared with macro scale systems, affirming the suitability of these techniques to electroanalytical applications and kinetic studies [24,25,26,27,28,29,30]. An experimental design strategy known as central composite design (CCD) was implemented to minimize the number of experiments required, and determine which variable (pH or NaCl concentration) has the greater influence on the corrosion of copper. This design strategy was able to reveal correlations between the pH and NaCl concentration
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