Interfacial Na⁺ Transport in the Beta Alumina/Propylene Carbonate System

Na⁺ transport across a polycrystalline β‐alumina/propylene carbonate interface has been studied at 23°C as a function of current density from 1.0 to 6600 μA/cm² under dry and hydrated conditions. Constant current transient analysis from 10⁻⁷ to 10² sec was used to distinguish interfacial and bulk resistivity components during ion entry into and exit from β‐alumina. The resistance associated with Na⁺ exit increases significantly after exposure of the β‐alumina to water vapor. Interfacial current/voltage relationships for dry and hydrated samples are nonlinear but qualitatively similar. Na⁺ entry phenomena are obscured by a steadily increasing interfacial resistance which accompanies ion transport into the β‐alumina, a process reversed by extended electrolysis out of the interface. The results suggest that interfacial transport involves an adsorbed intermediate state and is influenced by an equilibrium between adsorbed and substituted into the β‐alumina.