Vaporization study on the niobium monoxide and niobium metal systems by mass-spectrometric methods |
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Authors: | Tsuneo Matsui Keiji Naito |
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Affiliation: | Department of Nuclear Engineering, Faculty of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464, Japan |
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Abstract: | The vapor pressures over single-phase NbO(s) and two-phase NbO(s) — Nb(s) were measured by the mass-spectrometric method in the temperature range 1948–2301 K. The main vapor species over both systems were observed to be NbO(g) and NbO2(g). By applying the second and the third law treatments of thermodynamics to the partial vapor pressures of NbO(g) and NbO2(g), the enthalpies of vaporization were calculated for the following reactions: NbO(inNbO(s)) = NbO(g), NbO2(inNbO(s)) = NbO2(g), 2NbO(s) = Nb(s) + NbO2(g), 2NbO(s) = Nb(s)+NbO(g) + 0(g). The enthalpies of formation and the dissociation energies of NbO(g) and NbO2(g) obtained from these reactions were in good agreement with the previous results obtained from the vapor pressure measurements on NbO2(s) by the present authors. The partial pressures of oxygen were calculated as a function of temperature from the partial pressures of NbO2(g) and NbO(g), from which the partial molar enthalpies and entropies of oxygen in the system of NbO(s) and Nb(s) were determined. |
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