The Replacement of Titanium by Zirconium in Ceramics for Plutonium Immobilization

ABSTRACTZirconates and titanates, based on the nominal baseline composition developed for the Plutonium Immobilization Project (PIP), have been prepared with and without process impurities. The titanates form pyrochlore as the major phase and the zirconates form a defectfluorite. Little, if any, of each impurity is accommodated in the defect-fluorite and powellite, kimzeyite, a spinel and a silicate glass appear as extra phases in this ceramic. In the titanates the pyrochlore incorporates more impurities, with the remainder being accomodated in zirconolite and a small amount of silicate glass. At extremly high levels of impurities, traces of magnetoplumbite, perovskite, and loveringite were found. The defect-fluorite zirconate phase is more radiation damage resistant than the titanate pyrochlore, though the secondary phases in the zirconate will reduce the radiation damage resistance of zirconate monoliths. To produce a dense product the oxide-route zirconate required sintering temperatures of about 1550°C, 200°C higher than that required for the titanate. Silicate impurities reduce the sintering temperatures.