Effect of temperature on formation of murataite and murataite-pyrochlore ceramics

摘要

Processes of phases formation in the ceramic mixtures with basic compositions (wt.%) 10 CaO, 10 MnO, 5 Al_2O_3,5 Fe_2O_3, 55 TiO_2, 5 ZrO_2,10 UO_2 (M1) and 8 CaO, 8 MnO, 4 Al_2O_3, 4 Fe_2O_3, 20 Gd_2O_3, 44 TiO_2, 4 ZrO_2, 8 UO_2 (M4) were studied using X-ray diffraction, scanning and transmission electron microscopy. The batches were milled, compacted in pellets at 200 MPa, and heat-treated in a resistive furnace at 1100℃, 1300℃, 1400℃, and 1500℃ as well as melted in a cold crucible at ～1600 ℃. Reactions in the mixtures heat-treated at 1100 C were not completed and samples contained significant amount of unreacted and intermediate (altered rutile, cubic oxide solid solution, perovskite) phases. Within the temperature range 1100-1300℃ reactions are mainly completed and ceramics sintered at 1300℃ are composed of major murataite and minor rutile (M1) or major murataite and pyrochlore and minor zirconolite and perovskite (M4). However full homogenization at 1300℃ has not been reached yet and to obtain the ceramics with uniform compositions of the phases sintering at 1400℃ or melting at 1500-1600℃ were required. In the ceramic sample Ml two murataite varieties with five- (murataite-5C) and eight-fold (mu-rataite-8C) fluorite-type unit cells were found. The sample M4 is composed of pyrochlore, murataite-8C and zircqnolite-3O. In the sample Ml murataite-5C is enriched with U and Ca and depleted with iron group elements as compared to murataite-8C. Fraction of murataite-5C concentrates about 80% of total U and about 70% of Mn+Fe (corrosion products). Waste elements partitioning among the phases in the M4 sample depends significantly on temperature of heat-treatment.