Volume 5, number 1 I, 12 MATERIALS LETTERS October 1987 POTENTIODYNAMIC POLARIZATION BEHAVIOR OF YBazCu30,_, SUPERCONDUCTOR R.S. BHATTACHARYA, Yuan-Fu YU and A.K. RAI L%S zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Universal Energy Sysrems, Inc., 4401 Dayton-Xenia Road, Dayton, OH 45432, USA Received I7 August 1987 Aqueous corrosion behavior of YBa&u,O,_, superconductor was studied in 1 M H,SO, and 0.1 N NaCl solutions by the potentiodynamic polarization technique. The corrosion rate was found to be higher in I M HSO, than in 0.1 N NaCl solutions. In comparison to pure Cu, YBa#.Zu,O,_ r is more stable in these solutions. The discovery of high-temperature (90-100 K) superconductivity [ 1,2] in copper-containing oxides has sparked widespread speculations about their commercial applications. The possible application areas are in electronics and electricity, including computers, power transmission, transportation and medicine. Some applications of these new materials will be critically dependent on their stability to cor- rosive aqueous environments. In general, ceramics are insulators with better corrosion resistance prop- erties than metals. However, these new ceramic su- perconductors are conducting at room temperature having resistivities on the order of 5-l 5 rnfi cm. In terms of corrosion, it has been reported that the ma- terial is sensitive to water and carbon dioxide. It is, therefore, important to study the stability of this new class of materials in various environments. We have performed preliminary studies of corro- sion behavior of YBaZCu307~1 superconductor in aqueous acidic and alkaline solutions using the po- tentiodynamic polarization technique. The specimens were prepared by mixing BaCO,, YzO, and CuO powders in proper ratio. The mixed powder was first ball milled and then clacined at 950°C for 2 days. After calcination, the powder was grinded again and formed into pellets by mechani- cally pressing in a 1 inch stainless-steel die. The spec- imens were sintered under flowing oxygen gas at 965°C for 6 h and then slowly cooled to 300°C over a 12 h period. The powder X-ray diffraction of the samples exhibited identical pattern to that reported in the literature. The temperature dependence of the resistivity was measured and showed a sharp tran- sition at 91 K. The samples were polished with 600 grit SIC paper followed by 3 urn diamond paste on nylon and finally on colloidal silica microcloth (MastermitTM) and then cleaned by acetone and dried by blowing dry nitrogen. Electrochemical experiments were performed with a PARC model 332 tm softcorr corrosion software in conjuction with a PARC model 173 potentiostat/ galvanostat in solutions of 0.1 N NaCl and 1 M H,SO, at 25°C. The cell was left open to the at- mosphere, and no previous purging of 0, was at- tempted. All potentials reported throughout this paper are with respect to a saturated calomel elec- trode (SCE). Scans were always started at a cathodic potential of - 100 to -200 mV with respect to zyxwvutsrqpo E,,,, and continued until the potential reached to about 2500 mV at a scan rate of 1 mV/s. We have run pure Cu in the same solutions for a comparison with YBa2Cu307~n since Cu is the major metallic con- stituent of the compound and also because of the fact that it might replace Cu in electrical circuits as in- terconnects. The potential scan for Cu was run up to 1500 mV because of much higher dissolution rate of Cu in these solutions as compared to that of YBa2Cu@-x. In the case of YBa2Cu307_x samples, an area of 4.906 cm* was exposed to the solution whereas for Cu samples, the exposed area was 0.07 cm*. Several measurements were made to ensure the reproducibility of the electrochemical measure- 0167-577x/87/$ 03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division) 429