EMF Measurements of Sodium Activity in Sodium Amalgam with Beta-Alumina

Beta-alumina,2 nominal formula Na20"11A1203, has been used as a refractory material for decades (1, 2). Recently, Ford Motor Company has used it for de-veloping a sodium-sulfur battery system (3, 4). Emf measurements have been performed with beta-alumina to test for behavior as a solid electrolyte for measuring sodium activity in amalgams and to test the assumption that the conductivity of beta-alumina is ionic in nature. The latter is in contrast o potas-sium ferrite (5), an isomorphous compound of beta-alumina, for which the electrical conductivity is par-tially electronic and partial ly ionic. Emf measure-ments such as this can indicate if the electronic on-ductivity is high enough in a practical sense to cause interference with electrochemical measurements