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.

An approach to deoxidation of metals of the groups VB and VIB through “oxide removal” diagrams

“…Values of Po~,~, PM and Pj,~ used in calculations of R Ef, are evaluated from thermochemical data [10], are in good agreement with available experimental data, determined by mass spectrometry [11][12][13].…”

The σ–π transmitted coupling over five and six bonds in pyridine–borane complexes. MO calculations on structure and spin–spin couplings

“…somewhat larger than the benzene solution value of 5.86D (14). The B-N bond length of 1.647 A appears rather large, when compared to the X-ray value of 1.56 in NH,.BH, (15) or to the microwave value of 1.609 A in (CH,)N.BH, (16). In the latter the B-H length is 1.21 A and the NBH angle is 105.3".…”

Template Removal via Boudouard Equilibrium Allows for Synthesis of Mesostructured Molybdenum Compounds

“…[18] The former crystallizes in a distorted rutile structure and is electrically conductive. [19] In addition, MoO 2-x exhibits no appreciable vapor pressure [20] ( Figure 1a) and the collapse of the mesophase may therefore be avoided, while the p(O 2 ) is still high enough to ensure removal of the carbon scaffold (Figure 1b). Herein we describe a synthetic protocol towards 1D mesoporous MoO 2-x nanowires by endotemplating followed by subsequent carbothermal treatment in inert atmosphere and calcination under controlled p(O 2 ).…”

“…[20,23] Consequently, the described dilemma can be avoided by oxidizing the carbon scaffold at oxygen fugacities where MoO 2 is the stable phase. As shown in the Ellingham diagram (Figure 1b) the desired oxygen fugacity can be thermodynamically achieved by using CO 2 as oxidation agent.…”

“…MP and BP denote the melting point and boiling point. [20,24] Removal of the polymeric template was accomplished by two calcination steps: First, the sp 2 -hybridized carbon atoms of the ADM/PB-b-P2VP nanocomposites were converted in argon atmosphere at 973 K into a carbonaceous scaffold which stabilizes and lines the inorganic walls (Scheme 1C). Further details on this carburization reaction can be found in previous reports.…”