For future stationary energy storage requirements, sodium batteries are potentially suitable candidates owing to their high energy density, proven reliability, high faradaic efficiency and the use of abundant low-cost raw materials. Tubular battery designs require a thin-walled solid electrolyte tube, usually formed from ion-conductive beta″-alumina ceramic. State-of-the-art manufacturing methods, namely isostatic pressing and electrophoretic deposition, contribute a significant proportion of battery cost, and it is desirable to identify a high-volume low-cost process for the ceramic. Extrusion offers the potential for a rapid low-cost, high-volume production process but requires special development for adaptation to the demands of solid electrolyte production. This paper summarizes recent trials on extrusion as a process for producing beta″-alumina ceramic electrolyte tubes.

Microstructural characteristics of a gold-particle (GP)-reinforced glass-ceramic (GC) composite at the GP/GC interface were investigated before and after heat treatment at 900, 1100 and 1300 °C. The interfacial regions between the GP and GC exposed on the fracture surface and relevant chemical reactions were examined. The as-processed GC matrix had a nano-scaled biphasic microstructure, with isolated amorphous leucite phase evenly distributed in the continuous feldspar matrix. After the GP/GC composite was heated at 900 °C, the amorphous leucite phases were transformed into leucite crystalline phases. Au 2 Si and Au 5 Si 2 found at the GP/GC interface proved that chemical reactions had indeed occurred during composite processing. Fracture surface features around the GP and GP/GC interface were further examined after heat treatment at 1100 °C and 1300 °C, showing new compounds were produced during the process. Characterization techniques, including X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM), incorporating X-ray microanalysis using Energy-Dispersive Spectrometry (EDS), were employed to study the GP/GC interface.

Owing to their high refractoriness and slag resistance, high-alumina refractories are widely used in the lining of steelmaking furnaces, glass furnaces and cement rotary kilns in high-temperature industries. The impurities in the raw materials react to form the glass phase, which can melt into liquid at high temperatures. The modulus of rupture of refractories depends intensively on the content and composition of the glass phase. In this work, the cold and hot modulus of rupture for high-alumina bricks were investigated by means of fitting based on different theories. The effect of the glass phase on the modulus of rupture was analyzed by combining the phase composition, morphology of fracture surfaces and porosity for high-alumina refractories.

Beta-to-alpha transformation in cristobalite was examined by means of differential scanning calorimetry (DSC) to address how enthalpy, transformation hysteresis, and transformation onset temperature change upon repeated thermal cycling. Cristobalite powder was repeatedly cycled from 190 – 280 °C and back, cycling through the firstorder displacive transformation between high-temperature, cubic beta-cristobalite and low-temperature, tetragonal alpha-cristobalite. The enthalpy of the transformation did not changewith cycling, but the exothermic beta-to-alpha enthalpy at 1560 ± 27 J/mol was larger than endothermic alpha-to-beta enthalpy at 1260 ± 8 J/mol. Transformation onset temperatures and hysteresis varied systematically with repeated cycling of the transformation. The onset temperature of the beta-to-alpha transformation increased logarithmically with cycling, resulting in reduced undercooling and hysteresis. The onset temperature of the alpha-to-beta transformation decreased logarithmically with cycling, resulting in reduced super-heating and hysteresis. The reduced hysteresis indicates a lowered barrier to transformation. We propose this reduced hysteresis indicates particle refinement through microfracture caused by the -4.9% volume change on the beta-to-alpha transformation. This is supported by the observation of powder size dependence. Powder with particles finer than 38 μmhad no change on cycling, suggesting 38 μm is below the critical minimum size.