Dense polycrystalline strontium β′'- and β-alumina: Synthesis, XRD characterization and thermal stability

Dense polycrystalline ceramic tubes of strontium β′'- and β-alumina were prepared by ion exchange of sintered tubes of Li2O-stabilized Na β′'-alumina and of Na β-alumina at 585 ± 5°C in a molten eutectic mixture of SrCl2Sr(NO3)2. X-ray powder diffraction patterns are presented. The thermal stability of the materials was studied at temperatures up to 1550°C. Both Sr β′'- and β-alumina were found to be more stable than other M2+ substituted isomorphs. Sr β′'-alumina appears to be stable to at least 1100°C, but its stability decreases with an increasing β-phase content in the starting material. It transforms first to a β-alumina phase (<1250°C) and then gradually to a magnetoplumbite phase. Unstabilized Sr β-alumina starts to transform to a magnetoplumbite structure above 1000°C.