OPTICAL 2ND-HARMONIC GENERATION AS A PROBE OF SELECTIVE DISSOLUTION OF BRASS

A phenomenological framework is developed to explore the potential of surface second harmonic generation as a diagnostic tool of Zn dissolution from brass. A previously proposed model of selective dissolution is incorporated in this framework and tested experimentally by using a brass electrode (alpha-Cu0.63Zn0.37) in 0.1 M NaClO4. This electrode is subjected to voltage-controlled selective dissolution of its Zn sites, and the morphology of the dissolving surface is monitored with optical second harmonic generation employing two fundamental wavelengths, 1064 and 532 nm. At both wavelengths, the second harmonic intensities exhibit strong correlations with the electrochemical currents for Zn dissolution. These observed correlations are consistent with the theory presented. The results demonstrate how time-resolved information about surface reactions on binary alloys can be obtained with combined electrochemical and second harmonic generation techniques.