INFLUENCE OF BICARBONATE IONS ON THE STABILITY OF PREPASSIVE LAYERS FORMED ON COPPER IN CARBONATE BICARBONATE BUFFERS

The dissolution and passivation of polycrystalline copper (Cu) electro des in carbonate (CO32-)-bicarbonate (HCO3-) solutions covering wide r anges of pH and electrolyte compositions were studied at 25 degrees C, The influences of the CO32--HCO3- concentration ratio and hydrodynami c conditions on electrodissolution of the base metal, on formation of prepassivating and passivating surface layers, and on chemical dissolu tion of the prepassive films were considered, Results obtained with a rotating disc electrode allowed the competing reactions related to the active-to-passive transition to be distinguished through the effects of potential scan rate and electrode rotation speed on the electrochem ical behavior of the system at fixed concentrations of CO32- or HCO3-. Data were discussed on the basis of the interactions between HCO3- an d Cu(II) oxide and hydroxide anodic products in the prepassive surface layer.