Dense polycrystalline calcium β″- and β-aluminas: Synthesis, xrd characterization and thermal stability

Techniques for preparing dense polycrystalline Ca β″-alumina ceramic shapes by ion exchange of sintered Li2 O-stabilized Na β″-alumina containing between 5 and 19% of a β-phase have been examined. Preparation of Ca β-alumina by ion exchange has also been investigated. Nearly full exchange of both phases has been achieved in all cases. Both Ca β″- and β-alumina were found to be thermally unstable, transforming above 700°C progressively to a magnetoplumbite phase. X-ray powder diffraction patterns for Ca β″-alumina and for Ca β-alumina are presented. Direct synthesis by solid-state high temperature reactions leads only to the formation of the magnetoplumbite phase, regardless of the precursor materials.