EFFECT OF CARBON-DIOXIDE ON THE REACTION OF YBA2CU3O6.5-VAPOR(X WITH WATER)

The influence of carbon dioxide on the reaction between YBa2Cu3O6.5+x powder and air saturated with water vapour was studied. Superconductor powder samples were exposed to air that was saturated with water vapo ur which (a) was free of CO2, (b) was saturated with CO2, and (c) cont ained ambient levels of CO2. In another experiment, the effect of pure , dry CO2 (1 atmosphere partial pressure) was studied. The time variat ions of sample weight, oxygen content and X-ray diffraction (XRD) spec trum were determined. In water-saturated air, the rate of decrease of the oxygen content in YBa2Cu3O6.5+x decreased with increasing partial pressure of CO2. XRD was used to identify the reaction products. Highe r partial pressures of CO2 favour the formation of a barrier layer (Ba CO3) which inhibits the reaction of the underlying YBa2Cu3O6.5+x with water vapour. Very little decrease in oxygen content occurred on expos ure of YBa2Cu3O6.5+x to pure, dry CO2.