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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.

The evaporation of alumina under nearly neutral conditions in tungsten and molybdenum Knudsen cells has been investigated by mass spectrometric methods. The atomization energies of the gaseous molecules are D0o(AlO) = 115±5 kcal/mole; D0o(Al2O) = 245±7 kcal/mole; D0o(Al2O2) = 365±7 kcal/mole.

Partial pressures of the gaseous oxides MoO, MoO2, MoO3, WO, WO2, WO3, UO, UO2, and UO3 in the systems Mo–Al2O3 and U–Al2O3 have been measured by mass spectrometric methods. The vapor pressure of uranium has also been determined. The reaction enthalpies derived from these measurements are: Reaction         ΔH0ο kcal/moleMoO(g)→Mo(g)+O(g)         116±15MoO2(g)→Mo(g)+2O(g)         262±10MoO3(g)→Mo(g)+3O(g)         411±7WO(g)→W(g)+O(g)         154±10WO2(g)→W(g)+2O(g)         296±7WO3(g)→W(g)+3O(g)         443±7UO(g)→U(g)+O(g)         179±7UO2(g)→U(g)+2O(g)         340±7UO3(g)→U(g)+3O(g)         493±7U(s)→U(g)         126±5.

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