The standard gibbs energy of formation of CeF3 and its activity coefficient in cryolite

Literature data are analyzed to give the activity coefficient (γ_Ce) of Ce in dilute solution in Al as log₁₀γ_Ce = −11 356/T + 4.261 referred to liquid Ce as standard state. Measurements were made in the range of 977 to 1288 K of the equilibrium Al (1) + CeF₃ (s) = AlF₃ (s) + Ce(Al) and give, by a third-law calculation, °G ^o = 183 360 + 19.456T joules, and Δ _{fH 298} ^o of CeF₃ = −1701 kJ mol⁻¹. Values of the partition coefficient of Ce between Al and molten cryolite then give activity coefficients of CeF₃ in solution. These activity coefficients decrease as the NaF/AlF₃ ratio is raised, showing acid behavior of CeF₃. It appears to dissolve mainly in the form of Na₂CeF₅.