Thermodynamics of Evaporation of Yttrium Trifluoride in the Form of YF₃ and Y₂F₆

Treatment of the literature data on the vapor pressure of yttrium trifluoride using the new thermodynamic functions of YF₃ molecules gave a refined value of the sublimation enthalpy of yttrium trifluoride in the form of a monomer and the enthalpy of formation of YF₃(g). The quantum-chemical calculations of YF₃ and Y₂F₆ molecules were performed, and the energy of dissociation of the dimer molecules into two monomer molecules was calculated. Using these data, the enthalpy of sublimation of yttrium trifluoride in the form of a dimer was found, and the formation enthalpy of Y₂F₆(g) was calculated. The composition of the yttrium trifluoride vapor was calculated: the pressure ratio of Y₂F₆ and YF₃, P_d/P_m, in the range 1400–3000 K increased from ≈2 × 10^–4 to ≈2 × 10^–2. The obtained thermochemical values were entered into the database of IVTANTERMO software.