Thermodynamic study and assessment of the fluorine-iron system

International audienceUF6 molecule is utilized for enrichment of fissile uranium for nuclear power plant fuel. However, corrosion of steels structural materials can occur in UF6 production plants. Corrosion of steels in fluoride atmospheres leads to formation of iron fluorides FeF2 or FeF3 [1]. In order, to understand and then to model the corrosion mechanism, thermodynamics of the fluorine-iron system is required. A literature review on the phase diagram data and thermodynamic properties of this chemical system has pointed out the lack of reliable thermodynamic data - the melting temperature of FeF2 has to be confirmed; - the enthalpy of formation measurements of FeF3 are scattered;- the only phase diagram proposed in the literature is limited to the FeF2-FeF3 part [2];- and the Fe2F6 gaseous dimer has no available thermodynamic properties. Thus, both experimental and computational works were carried out to improve the thermodynamic knowledge of this system. In this study, differential thermal analysis experiments were performed to measure the liquidus temperatures in the FeF2-FeF3 part and to determine transition temperatures in the Fe-FeF2 part. Moreover, calculations using the Density Functional Theory method permitted to obtain thermodynamic properties of Fe2F6 gaseous molecule.Finally, CALPHAD method, taken into account the previously obtained data and a former database, has been used to improve the thermodynamic description of the system Fe-F