THERMODYNAMIC MODELING OF CHEMICAL INTERACTIONS BETWEEN CAO-TIO2 CERAMICS AND MOLTEN-SALTS

The mixed-oxide compounds of CaO with TiO2 are of interest in the deve lopment of container vessels for actinide recycling processes in which Ca (dissolved in molten salt) is used to reduce the actinide oxide to actinide metal. The chemical interactions between the mixed-oxide com pounds and molten salt saturated with Ca have been analyzed by applyin g thermodynamic principles. Although the solubility of CaO in molten s alt is suppressed by the formation of mixed oxide with TiO2, thermodyn amic calculations show that corrosion of CaO-TiO2 ceramics by molten C aCl2 or CaCl2-20 mole % CaF2 that contains metallic Ca in solution occ urs by dissolution of the CaO component of the mixed-oxide compounds i n the molten salt and reduction of the TiO2 component by the metallic Ca. The thermodynamic predictions are consistent with the experimental observations. The corrosion products produced and the sequence of the various phases depend upon the activity of the Ca produced in the mol ten salt by reduction reactions. The results of this study show that c eramic materials in the CaO-TiO2 system are not suitable container mat erials for actinide recycling.