Self-propagating high-temperature synthesis of Ce-bearing zirconolite-rich minerals using Ca(NO3)2 as the oxidant

Synroc is recognized as the second generation waste form for the immobilization of high-level radioactive waste (HLW). Zirconolite-rich (CaZrTi 2 O 7 ) Synroc minerals were attempted by self-propagating high-temperature synthesis (SHS) using Fe 2 O 3 , CrO 3 , Ca(NO 3 ) 2 as the oxidants and Ti as the reductant . All designed reactions were ignited and sustained using Ca(NO 3 ) 2 as the oxidant, and zirconolite-rich ceramic matrices were successfully prepared with pyrochlore (Ca 2 Ti 2 O 6 ), perovskite (CaTiO 3 ) and rutile (TiO 2 ) as the minor phases. The sample CN-4, which was designed using Ca(NO 3 ) 2 as the oxidant with TiO 2 /Ti ratio of 7:9, was readily solidified with density of 4.62 g/cm 3 and Vickers hardness of 1052 HV. CeO 2 was successfully stabilized by the CN-4 sample with resultant phase constituent of 2M-CaZrTi 2 O 7 and CaTiO 3 .