Mass Spectrometric Investigation of the Sublimation of Molybdenum Dioxide

Abstract

A mass spectrometric investigation of the vapor in thermodynamic equilibrium with powdered molybdenum dioxide has shown the vapor phase to consist, in decreasing order of importance, of the species MoO3, (MoO3)2, MoO2, and (MoO3)3. The heats, entropies, and free energies of reaction have been determined for the reactions (T=1600°K): 32x MoO2(s)→(MoO3)x(g)+12x Mo(s) where x=1, 2, 3MoO2(s)→MoO2(g) ΔHT=134.4±7 kcal/mole2MoO3(g)→(MoO3)2(g) ΔHT=−110.2±8 kcal/mole3MoO3(g)→(MoO3)3(g) ΔHT=−222.8±13 kcal/moleFor the case x=1, 2, 3 the ΔHT's are 121.8±3, 133.4±7, and 142.6±13 kcal/mole, respectively. Entropies of the gaseous molecules MoO3, (MoO3)2, (MoO3)3, and MoO2 at T=1600°K are 96.6, 151.0, 201.2, and 85.5 eu, respectively. In addition, the atomization energies (ΔH0o) for the reactionMoOx(g)→Mo(g)+xO(g)were calculated to be 277.4±7 and 419.7±10 kcal/mole for x=2 and 3, respectively.