Hot pressing of lithia-stabilized β″-alumina

Fine-grained (< 5μm), dense (3.26–3.27 g/cm³), and strong (> 200 MN/m²) polycrystalline β″-alumina (lithia-stabilized) ceramics can be fabricated by vacuum hot-pressing at temperatures ≥ 1330°C and pressures between 28 and 41 MN/m². By suitable low temperature annealing (< 1400°C), a fine-grained, high strength β″ alumina body can be fabricated with a low resistance (< 5 ohm-cm at 300°C) to sodium ion conduction. The relatively high sodium ion resistivities (6–11 ohm-cm) obtained directly after hot-pressing are caused by an incomplete phase conversion to β″-alumina during densification and not to a small grain size. Low temperature annealing can promote phase conversion and yet prevent any significant grain growth. The high strength ceramics produced by hot-pressing can serve as the standard to be achieved in conventional sintering.