Mass Spectrometric Study of Gaseous Molybdenum, Tungsten, and Uranium Oxides

Abstract

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.

Thermodynamics of the O–U system. IV – Critical assessment of chemical potentials in the U–UO2.01 composition range

“…These proportions can be changed by oxidation or deoxidation with surface reactions depending on the cell and furnace materials together with the quality of the vacuum system. Usually as observed by De Maria et al [74], Pattoret, Drowart and Smoes [59,61,62], and Storms [63] these contribution for the U-O system are more pronounced for reductive species (U > UO > UO 2 ). Indeed Pattoret and coworkers did not detect any contribution for UO 2 (g), with their mobile slit device, and the UO 2 'slit profile' served as a reference (see Fig.…”

“…The reactivity of the U-O system is also relevant outside the effusion cells, since many authors observed parasitic molecular flows additional to the genuine effusion flow that is the only flow appropriate to the studied equilibrium. In original and earlier mass spectrometric devices, as for instance in the study of gaseous U-O system, De Maria et al [74] observed with a mobile slit interposed between the effusion orifice and the ion source aperture that surface vaporizations (Fig. 12(c)) contributed to the detected flow; the more reducing the original vapour, the more additional contribution was observed.…”

“…In a first step the surface diffusion increases, but very suddenly above some temperature threshold, creeping is occurring. The mobile slit device is very efficient for determining this onset as shown by De Maria et al [74] and Pattoret et al [59][60][61][62]. The effect of the creeping on second law results is the reverse of the surface diffusion effect.…”

“…Parasitic surface evaporations as observed in the study of the U-UO 2 system by Knudsen-cell mass spectrometry using a mobile slit profile device: (a) from de Maria et al[74]; (b) from Pattoret and coworkers[59][60][61][62].…”

Ionization potentials and bond energies of TiO, ZrO, NbO and MoO

“…In 1959, DeMaria et al 10 in a Knudsen-effusion massspectrometric study used an extrapolation of the ionization efficiency curve to obtain an ion-appearance potential of IP͑MoO͒ϭ8.0Ϯ0.6 eV. Finally, using the density functional calculation mentioned above Broclawik 49 determined the IP͑MoO͒ to be near 8.03 eV.…”