Effect of carbon dioxide on the reaction of YBa2Cu3O6.5+x with water vapour

Superconductor powder samples were exposed to air that was saturated with water vapour which (a) was free of CO2, (b) was saturated with CO2, and (c) contained ambient levels of CO2. In another experiment, the effect of pure, dry CO2 (1 atmosphere partial pressure) was studied. The time variations of sample weight, oxygen content and XRD spectrum 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. Higher partial pressures of CO2 favour the formation of a barrier layer (BaCO3) which inhibits the reaction of the underlying YBa2Cu3O6.5+x with water vapour. Very little decrease in oxygen content occurred on exposure of YBa2Cu3O6.5+x to pure, dry CO2. 13 refs.