Thermodynamic investigation of the LiF–ThF4 system

A thermodynamic investigation of the LiF–ThF4 system is presented in this study. The enthalpy of mixing of the (Li,Th)Fx liquid solution was measured for the first time using a method designed for conventional DSC technique. To verify the possibility to measure the mixing enthalpy with the used calorimeter, the known LiF–KF system was first investigated and compared to the literature data. After the successful test, this technique was applied to investigate the LiF–ThF4 system and obtained novel results are presented in this study. Furthermore, using the DSC technique, new equilibrium data of the LiF–ThF4 phase diagram were measured, confirming the stability of the LiThF5 phase. The intermediate compound Li3ThF7 was synthesized and its enthalpy of fusion was determined. Considering the new experimental data, the LiF–ThF4 system was re-optimized using a quasi chemical model for the description of excess Gibbs parameters of the liquid solution.

► The technique to measure mixing enthalpies of fluoride liquid solutions using conventional DSC is presented.
► The mixing enthalpies of the (Li,Th)Fx were measured for the first time.
► New equilibrium data of the LiF–ThF4 system were obtained.
► The LiF–ThF4 phase diagram was re-assessed estimating heat capacity value of liquid ThF4.