Abstract:
Effusion-mass spectrometric studies were performed on the vapour species in equilibrium above VN(c) in the temperature range 1900 to 2412 K. From an analysis of the reactions involved, ΔHf298 values of 122.4 ± 5 kcal/mol (second law) and 120.4 ± 2 kcal/mol (third law) were obtained for VN(g), yielding a dissociation energy, D°298, for gaseous VN of 114.1 kcal/mol. An appearance potential of 8 ± 1 eV was recorded for VN(g). The thermodynamic analysis of the vapour species over the solid state yielded a second law ΔHf of –52 ± 1.5 kcal/mol for VN(c). Studies made in this temperature range resulted in a third law heat of fusion of 4.30 ± 0.45 kcal/mol for vanadium. The second and third law mass spectrometric ΔHf298 values of 122.8 ± 1.5 and 123.0 ± 0.2 kcal/mol, respectively, for V(g) were in good agreement with Knudsen third law weight loss experiments at 2092 and 2122 K, which yielded ΔHf298 values of 123.3 and 122.9 kcal/mol.
