MASS SPECTROMETRIC DETERMINATION OF THE DISSOCIATION ENERGY OF VANADIUM AND CHROMIUM DICARBIDE AND VANADIUM TETRACARBIDE

摘要

The Knudsen effusion method was used in conjunction with a double-focusing mass spectrometer to study the vaporization of the vanadium-carbon and chromium-carbon systems over the temperature ranges 2417 to 2603 and 2083 to 2176 K, respectively. The molecular species VC2, VC4, and CrC2 were identified, and experimentally determined third-law enthalpies were combined with published thermodynamic data to yield the following dissociation energies:nVC2(g) = V(g) + C2(g) Do° (V"C2) = 570±20 kJ/molenVC4(g) = V(g) + 2C2(g) Do°(C2-V-C2) = 1193±22 kJ/molenCrC2(g) = Cr(g) + C2(g) Do°(Cr-C2) = 445±18 kJ/molenAtomization energies were also calculated. Results are discussed in terms of the metal oxide - metal dicarbide bond strength analogy.