Mass spectrometric studies at high temperatures—X: The sublimation pressures of scandium (III), yttrium (III) and lanthanum (III), trifluorides

Abstract

Sublimation pressures of ScF 3, YF 3 and LaF 3 were measured by mass spectrometric and semi-microbalance studies via the Knudsen and Langmuir techniques. The mass spectrometric work established ScF 3(g), YF 3(g) and LaF 3(g) as the major vapour species over their respective solid trifluorides. For ScF 3 the results are represented by: log P atm = −(1·938 ± 0·042) × 10 4/ T + 9·43 ± 0·33; (1172° < T° < 1402°K) for YF 3 by log P atm = −(2·185 ± 0·030) × 10 4/ T + 9·77 ± 0·23; (1256° < T° < 1434°K) and for LaF 3 by log P atm = −(2·02 ± 0·02) × 10 4/ T + 8·20 ± 0·15, (1200° < T° < 1434°K) where the errors quoted are standard deviations from the least-square fits. The heat of sublimation for ScF 3 at 1290°K is 89 ± 3 kcal mole −1; for YF 3 at 1332°K, ΔH° = 100 ± 3 kcal mole −1; and for LaF 3 at 1324°K, ΔH° is 92 ± 2 kcal mole −1.