Vaporization Study of YbCl3, YbBr3, YbI2, LuCl3, LuBr3, and LuI3 and a New Assessment of Sublimation Enthalpies of Rare Earth Trichlorides

Abstract

The vapor pressures of YbCl3, YbBr3, YbI2, LuCl3, LuBr3, and LuI3 were measured by torsion and Knudsen effusion methods. Their temperature dependences may be reported as follows: YbCl3(s): log(p/kPa) = (11.30 ± 0.20) − (14420 ± 200)/(T/K) from (944 to 1096) K; YbBr3(s): log(p/kPa) = (11.51 ± 0.20) − (14070 ± 300)/(T/K) from (891 to 1032) K; YbI2(s): log(p/kPa) = (9.37 ± 0.30) − (13580 ± 300)/(T/K) from (968 to 1049) K; YbI2(l): log(p/kPa) = (9.04 ± 0.25) − (13220 ± 300)/(T/K) from (1068 to 1192) K; LuCl3(s): log(p/kPa) = (11.68 ± 0.15) − (14940 ± 150)/(T/K) from (942 to 1075) K; LuBr3(s): log(p/kPa) = (11.34 ± 0.20) − (14040 ± 300)/(T/K) from (903 to 1038) K; LuI3(s): log(p/kPa) = (11.99 ± 0.40) − (14270 ± 300)/(T/K) from (862 to 1004) K. Treating the vapor pressures of YbCl3 and LuCl3 by second- and third-law, the following standard sublimation enthalpies, ΔsubH°(298 K) = (288 ± 6) and (295 ± 5) kJ·mol-1, respectively, were derived. Comparison of these enthalpies with those of other rare earth trichlorides, recalculated by using a new set of thermodynamic functions, was made. From the YbBr3, LuBr3, and LuI3 vapor pressures, the second-law sublimation enthalpies, extrapolated at 298 K by estimated enthalpic increments, ΔsubH°(298 K) = (285 ± 9), (285 ± 9), and (288 ± 9) kJ·mol-1, respectively, were evaluated. For YbI2, ΔsubH°(298 K) = (302 ± 6) kJ·mol-1 was obtained by use of thermal functions estimated by analogy with the published data on EuI2.