The synthesis of beta-alumina using the rapid heat resin-gel method

Abstract

Beta-alumina is a ceramic oxide that exhibits high conductivity of sodium ions, this plays a fundamental role allowing beta-alumina to be used as solid Na+ conducting electrolyte membrane that separates a sodium anode and a cathode of either sulphur or metal halide in high energy density batteries. Traditionally, high dense sodium betaalumina solid electrolyte has been made by solid-state reactions. The effect of using a novel route to synthesise beta-alumina was investigated. Samples of magnesium stabilised sodium β and β” alumina composites were prepared by resin-gel pyrolysis using non-stoichiometric amounts of metal nitrates and citric acid. A series of composites (Al11-xMgO16)(Na1+xO) of different compositions 0.45 ≤ x ≤ 0.65 were synthesised. Molecular weight of the polyethylene glycol (PEG) used in the synthesis of composites was varied. The post-treated composite was calcined at several temperatures (700-1500°C). Variable temperature powder X-Ray diffraction showed phase changes that occur from 30-926°C. However, there was an additional phase change at 1100-1200°C to convert the composite to either β or β” alumina. The post-treated composite was sintered into 20 mm discs using spark plasma sintering and characterised. The characterisation techniques used in this study was electron probe micro-analysis, energy dispersive X-Ray spectroscopy, scanning electron microscopy, thermogravimetric analysis, powder X-Ray diffraction, and variable temperature powder X-Ray diffraction. The results confirmed that resin-gel synthesis could produce a composite that could be converted into beta-alumina. The morphologies formed in the experimental composites also were favourable for strengthening the beta-alumina sintered bodies.