Thermal Characterization of Rhombohedral Ceramics (RE₆UO₁₂) of Interest in Nuclear Industry

ABSTRACT

Enthalpy increments of the ternary compounds of rare earth uranium oxides, RE₆UO₁₂ (RE = La, Nd, Sm, Eu, Gd) were measured by inverse drop calorimetry in the temperature range 533-1738K. These compounds (RE₆UO₁₂) were prepared by gel combustion synthesis and characterized by XRD. From the measured enthalpy increment values, thermodynamic functions, viz. heat capacity, entropy, Gibb's energy functions were computed. The trend in variation of heat capacity was in the order: Eu₆UO₁₂>Sm₆UO₁₂>Nd₆UO₁₂>La₆UO₁₂>Gd₆UO₁₂. This trend is explained based on (i) phonon (ii) dilatational and (iii) Schottky contributions to the heat capacity. The trend in variation of heat capacity of RE₆UO₁₂ is similar to that of RE₂O₃.

GRAPHICAL ABSTRACT

Keywords:

• Rhombohedral ceramics
• Nuclear industry
• Rare earth uranates
• Thermal properties
• Calorimetry