Phase and structural evolution of zirconolite ceramics prepared by solid-state reaction sintering

Abstract

The evolution of phase assemblage and microstructure of stoichiometric zirconolite (CaZrTi 2 O 7 ) ceramics, prepared by a solid-state reaction sintering route, was systematically investigated as a function of sintering temperature. Using powder XRD and quantitative phase analysis data, it was determined that the formation of zirconolite was a one-step reaction, without formation of intermediate phases. The accompanying fractions of secondary CaTiO 3 and ZrO 2 phases were reduced to approximately 2 wt % each after sintering at 1200 °C, with zirconolite formed as the major phase (> 99 wt%) after reaction at 1300 °C. Notable product densification only occurred at T ≥ 1400 °C, at which it was possible to achieve a relative density of 96.97% which is highly desirable for applications as a nuclear wasteform. The zirconolite-2M polytype structure (space group: C2/c) was formed in all products as expected, confirmed by combined high resolution TEM-ED analyses.