Sodium-rich solid state reaction synthesis of sodium tri-titanate for AMTEC application

Abstract

Alkali-Metal-Thermal-Electric-Converter systems (AMTEC-systems) pose a promising approach for energy conversion, e.g. from waste heat. Central components are a gas-tight ion-conductive solid membrane and an enclosed porous electrode. The presented study covers an adapted synthesis routine for single-phase sodium-tritanate (Na2Ti3O7) and its assessment as an alternative AMTEC-membrane-material. In contrast to the conventional stoichiometric solid state reaction between sodium carbonate and titania, the adapted synthesis reaction was performed with sodium excess. Up to 900 °C, the as-synthesised material evinced both, a constant thermal expansion behaviour over various thermal cycles and an expected electric conductivity. More important, phase stability either in pure state as well as in contact with a potential electrode material (La0.8Sr0.2)0.98MnO3 was demonstrated by long term exposure at 900 °C over 240 h. According to those findings the synthesised Na2Ti3O7 is considered to be an alternative membrane-material for AMTEC-application.

Keywords

• Alkali metal
• Sodium titanate
• Electrochemical impedance spectroscopy
• Chemical stability
• Thermal expansion