Temperature and Enthalpy of Fusion of Nanooxides UO2 and ThO2 of Different Morphologies

The dependence of the melting temperature and enthalpy of fusion on the characteristic size and morphology of nanoobjects consisting of UO₂ and ThO₂ was studied by the thermodynamic method. The influence of the characteristic size and morphology on the enthalpy of fusion and melting temperature of UO₂ and ThO₂ nanoobjects becomes noticeable when their characteristic size is less than 20 nm. The melting point abruptly decreases when the characteristic size of nanoparticles, nanowires, and thin films of UO₂ and ThO₂ is less than 5, 4, and 3 nm, respectively. The size effect decreases in a sequence: spherical nanoparticles–nanowires–thin films in all cases. The size effect also decreases when individual UO₂ and ThO₂ nanoparticles are combined into nanostructured nanoobjects. The results of calculations obtained in the present study are in good agreement with the results of calculations obtained by molecular dynamics and experimental data available in the literature.