Galvanic corrosion of Y-Ba-Cu-O superconductors by gold and aluminium

Cuprate-based high-Tc superconductors have formal Cu(II)/Cu(III) mixed valency states signifying the presence of a highly oxidised species, either Cu(III) or, more probably a complex peroxide (Cu(II)-O)-. This contributes to their environmental instability and it is now clear that degradation of oxide superconductors proceeds not only by chemical reactions but also by electrochemical reduction of the oxidised species present. For example, YBa2Cu3O7-x is thermodynamically unstable in the presence of water and oxygen is slowly evolved from aqueous solutions. Given the high oxidation potential of the superconductor further reactions, notably oxidation of contact metals, are likely. The authors report measurements of the rates of electrochemical corrosion of gold and aluminium by YBa2Cu3O7-x, which is also the first confirmation that gold is susceptible to galvanic corrosion. In 0.6 M NaCl solution, measured galvanic currents were consistent with rapid corrosion rates of about 0.5 mu m/day and 30 mu m/day for gold and aluminium, respectively.