The Replacement of Titanium by Zirconium in Ceramics for Plutonium Immobilization

Zirconates and titanates, based on the nominal baseline composition developed for the Plutonium Immobilization Project, have been prepared with and without process impurities. The titanates form pyrochlore as the major phase and the zirconates form a defect-fluorite. Very little, if any, of each impurity is accommodated in the defect-fluorite with powellite, kimzeyite, a spinel and a silicate glass appearing as extra phases in this ceramic. In the titanate ceramics the pyrochlore incorporates more impurities, with the remainder forming zirconolite and a small amount of silicate glass. At extreme 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 appreciably