Vaporization reactions in the thulium-fluorine system

Abstract

The vaporization and sublimation reactions for the thulium-fluorine system have been investigated by mass-loss, X-ray powder diffraction and elemental analysis techniques. Thulium trifluoride was reduced only partially by elemental thulium; a reduced stoichiometric fluoride could not be isolated. Partially reduced TmF 3 decomposes upon heating to a metal-rich vapor and a trifluoride-enriched residue. By a target collection Knudsen effusion method, equilibrium vapor pressures were determined for the reaction TmF 3( s, l)= TmF 3( g). From the slope-intercept data, the following thermodynamic changes with associated standard deviations were derived: ΔH° 1579 = (86.2 4 ± 0.4 8) kcal mol −1 and gDS° 1579 = (34.9 5 ± 0.3 2) cal mol −1 K −1. Use of estimated and reported thermodynamic functions gives ΔH° 298 = (108 .2 ± 1 .5) kcal mol −1and gDS° 298 = (55 .4 ± 1 .3) cal mol −1 K −1. Use of the third-law procedure yielded ΔH° 298 = (107 .5 ± 2 .3) kcal mol −1. The derived thermodynamic values are compared with those of other lanthanide fluoride systems.