Investigating the effect of particle size on microstructure, mechanical properties and electrical conductivity of sodium beta-alumina ceramics

The microstructure control of sodium beta-alumina electrolyte used in the manufacture of sodium sulfur batteries is important for obtaining appropriate mechanical and ionic conductivity properties. In this research, the effect of particle size of sodium beta-alumina powder on the final microstructure and properties of this ceramic has been investigated. For this purpose, solid-state-synthesized sodium beta-alumina powder was milled by attrition milling for 30 min, 2, 6, and 10 hours. The results showed that the milling time had a significant effect on the powder particle size and consequently on the condensation behavior, microstructure, and finally on the fracture strength and ionic conductivity of sodium beta-alumina electrolyte. By increasing the milling time from 30 minutes to 6 hours and reducing the average particle size of the powder from about 2 to 0.7 microns, the resulting powder condensation behavior improved due to increased sintering diving force, resulting in increased fracture strength and ionic conductivity of up to 65% and 100%, at high temperatures. With increasing the milling time to 10 hours, due to the development of non-uniform microstructure, a decrease in the mechanical and electrical properties of sodium beta-alumina ceramic was observed. The results of this study also showed a linear relationship between the fracture strength and the density of the samples can be established.