Experimental mixing enthalpy and thermodynamic modelling of UCl3-KCl system

The molar enthalpies of mixing (Delta H-mix(m)) in the liquid potassium chloride-uranium(III) chloride mixtures have been measured with a Calvet-type high temperature microcalorimeter over the entire composition range at 1113 K. All the melts are characterized by negative enthalpies of mixing with a minimum value of about -17.5 kJ.mol(-1). The minimum of the enthalpy of mixing is shifted towards the potassium chloride-rich compositions and located in the vicinity of XUCl3 similar to 0.40. The obtained results are discussed in terms of complexes formation in the liquid mixtures under investigation. Experimental mixing enthalpy data were used together with existing literature data in re-examination of KCl-UCl3 phase diagram. Analysis of the literature data on KCl-UCl3 phase diagram has indicated that all of them are not correct because the existence of K3UCl6 compound was ignored in spite of experimental facts pointing its existence. Reinterpretation of all existing data by CALPHAD method showed that the system under investigation is characterized by existence of K2UCl5 and K3UCl6 congruently melting compounds, and three eutectics (KCl-K3UCl6, K3UCl6-K2UCl5 and K2UCl5-UCl3, respectively). K3UCl6 solid compound exists at relatively narrow temperature range from about 800 K to congruent melting at about 892 K. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The molar enthalpies of mixing in liquid potassium chloride-uranium(III) chloride mixtures were measured at 1113 K, showing negative enthalpies with a minimum value of about -17.5 kJ/mol. The existence of complexes in the liquid mixtures was discussed based on the obtained results, re-examining the KCl-UCl3 phase diagram with the inclusion of K3UCl6 compound.