PRODUCTION AND CHARACTERIZATION OF POLYCRYSTALLINE (NA, CA)BETA''-ALUMINA

Polycrystalline (Na, Ca) beta"-aluminas with different calcium contents were produced from commercial Na beta"-alumina (Ceramatec Inc.) by ion exchange in suitable mixtures of NaNO3 and Ca(NO3)2. The extent of crack and pore formation could be reduced by increasing the calcium content gradually from one equilibrium concentration in the solid electrolyte to the next - higher one. The equilibrium distribution curve was determined for the polycrystalline materials and compared with measurements on single crystals. Thermogravimetric measurements were made on fully-exchanged samples. The curves of the specific conductivity versus the extent of exchange suggest that the Na+ ion is the conducting species in a wide range of soda content. The transition to the predominant conduction by the Ca2+ ion occurs in a relatively narrow region at high extents of exchange,