ON THE VAPOURIZATION THERMODYNAMICS OF COBALT TRIFLUORIDE

The sublimation of CoF3(s) was studied. The temperature dependence of the total vapour pressures as measured by the torsion method in the te mperature range 700-830 K fit on the equation: log(p/kPa)=(11.60+/-0.2 0)-(10630+/-400)/(T/K) Both the sublimation reactions: CoF3(s) = CoF3( g) (1) 2 CoF3(s) = 2 CoF2(s) + F-2(g) (2) occur during the vapourizati on of CoF3(s) where the molar fraction of the reaction (1) was found e qual to 0.60+/-0.05, practically constant in the covered experimental temperature range. The standard enthalpies Delta(sub)H degrees(298)=21 6+/-4 and 204+/-3 kJ mol(-1) for reactions (1) and (2) respectively we re derived from second- and third-law treatment of the data. New value s for the enthalpy of formation of CoF3(s) and CoF3(g) equal to -773+/ -5 and -557+/-10 kJ mol(-1), respectively, were derived. (C) 1997 Else vier Science S.A.