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Solidus and liquidus of UO2+x from high-pressure melting experiments
Dario Manara, Claudio Ronchi, Mikhail Sheindlin

An experimental investigation of the melting properties of stoichiometric and hyperstoichiometric uranium dioxide is presented. Self-crucible melting of UO2+x with different oxygen-to-metal ratios was produced by laser heating under an inert gas at pressures up to 0.25 GPa. The temperatures of phase transitions, measured by a fast pyrometer, were detected by thermal arrest analysis. The first part of the work was devoted to the measurements of the pressure dependence of the melting temperature of stoichiometric uranium dioxide. Comparison of these results with established thermodynamic data confirmed the reliability of the experimental method, which was then applied to the UO2+xsystem. Melting-point measurements on hyperstoichiometric uranium dioxide specimens have been carried out and are discussed. An improved UO2+x state diagram in the domain of the solid – liquid transition is proposed.

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