ELECTROCHEMICAL-BEHAVIOR OF THE SUPERCONDUCTOR YBA2CU3O7-X IN SOLUTIONS CONTAINING VARIOUS ANIONS

YBa2Cu3O7-x exhibits high open circuit potentials in aqueous solution over a range of pH with oxygen evolution, and reduction of the superco nductor, respectively the anodic and cathodic reactions. Potentiodynam ic polarization measurements in solutions buffered at pH 4.6 and 9.2 i ndicate that the Tafel slopes for these two reactions are 120 and 180 mV decade-1 respectively. The anodic Tafel slope is consistent with ox ygen evolution involving a rate-limiting one-electron transfer step. T he higher value of the cathodic Tafel slope suggests that the cathodic process is partially diffusion-limited. Addition of Cl-, SO42- and F- ions to the electrolytes indicate that solution pH, film formation on the superconductor surface, the solubility of degradation products an d complexing of ions in solution play important roles in the corrosion behaviour of YBa2Cu3O7-x. In particular, additions of sulphate ion an d fluoride ion significantly reduce the rate of degradation of YBa2Cu3 O7-x.