Oxygen permeation in bismuth-based materials. Part II: Characterisation of oxygen transfer in bismuth erbium oxide and bismuth calcium oxide ceramic

The¹⁸O/¹⁶O Isotope Exchange Depth Profile technique was applied to BE25 ((Bi₂O₃)_0.75(Er₂O₃)_0.25) and BICAO ((Bi₂O₃)_0.73(CaO)_0.27) dense ceramics to characterise the oxygen transfer in these materials. Pure ceramics, ceramics coated with silver on the surface and 40% silver cermets were investigated. Slow oxygen surface exchange kinetics were confirmed for the pure ceramics whilst the kinetics were improved when silver was painted on the surface. However oxygen permeation fluxes were not improved when a silver paste was painted onto the membrane surface. Permeation was also limited by electronic conduction which is likely to be more limiting than oxygen exchange at the surface of these ceramics. In contrast, fast kinetics of oxygen surface exchange were revealed for cermets.