A thermodynamic study of the molybdenum-oxygen system

Bygdén, Johan; Sichen, Du; Seetharaman, Seshadri

doi:10.1007/bf02662770

Cited by 23 publications

(12 citation statements)

References 21 publications

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“…The result of T / K FIGURE 4. Difference between the standard Gibbs free energy of formation, D f G (MoO 2 ), reported in the literature and that obtained in this study, as a function of temperature T: }, Tonosaki [1]; ,, Gokcen [2]; ·, Gleiser and Chipman [3]; ., Vassilev et al [4]; r, Rapp [5]; +, Barbi [6]; w, Drobyshev et al [7]; n, Berglund and Kierkegaard [8]; l , Alcock and Chan [9]; m, Iwase et al [10]; h, Kleykamp and Supawan [11]; , Pejryd [12]; s, O'Neill [13];¯, Bygden et al [14]; , Jacob et al [15]; j, JANAF (1985) [27]; and d, Pankratz [28]. Kleykamp and Supawan [11] at T = 1323 K agrees well with this study, but their results at lower temperatures are more positive.…”

Section: Resultsmentioning

confidence: 99%

“…For the calibration of oxygen sensors, accurate data on Gibbs free energy of formation of MoO 2Àd is necessary. Gibbs free energy of formation of MoO 2Àd has been measured by a number of investigators using CO + CO 2 or H 2 + H 2 O gas-equilibrium [1][2][3][4] and oxide solid electrolyte techniques using a variety of reference electrodes [5][6][7][8][9][10][11][12][13][14][15]. However, there is considerable difference in reported results, part of which is caused by the uncertainty in the oxygen potential of the reference electrode.…”

Section: Introductionmentioning

confidence: 99%

“…studies on MoO 2Àd zirconiabased solid electrolytes were used. Thoria-based electrolyte was employed in one study [14]. At high temperatures, the oxygen chemical potential at the Mo + MoO 2Àd electrode is close to the boundary for predominant ionic conduction (oxygen transport number >0.99) in stabilized-zirconia electrolytes [17,18].…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Thermodynamic evidence for phase transition in MoO2−δ

Jacob

Saji

Gopalakrishnan

et al. 2007

The Journal of Chemical Thermodynamics

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Thermodynamic evidence for phase transition in MoO2−δ

Jacob

Saji

Gopalakrishnan

et al. 2007

The Journal of Chemical Thermodynamics

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“…For example, Du Sichen and Seetharaman [7] [10] Other authors [11] reported the intermediate phase Mo 4 O 11 before reaching the MoO 2 phase by hydrogen reduction at 823 K. Ressler et al [12] studied the reduction of MoO 3 with hydrogen in the temperature range from 623 to 823 K and hydrogen concentration from 5 to 100 vol pct. They found that Mo 4 O 11 forms only under certain reaction conditions (H 2 concentration <20 vol pct and at temperatures above 698 K), where the reduction of MoO 3 is considerably slow that it permits the formation of Mo 4 O 11 .…”

Section: A Isothermal Reductionmentioning

confidence: 98%

Reduction Kinetics of Ag2MoO4 by Hydrogen

Juárez

Morales

2008

Metall Mater Trans B

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powders were mechanically (ball) milled with the objective of obtaining a Ag 2 MoO 4 phase for subsequent reduction with hydrogen gas. A thermogravimetric unit was used to follow the course of the reduction process aiming at the chemical reaction as the rate controlling step. Isothermal reduction experiments were performed on the individual oxides to establish a ground for the reduction parameters of silver molybdate. Consequently, a nonisothermal treatment was used on Ag 2 MoO 4 . It was found that Ag 2 MoO 4 is reduced in three steps, e.g., Ag 2 MoO 4 to MoO 3 and Ag followed by MoO 3 to MoO 2 and finally MoO 2 to Mo. By assuming a shrinking core model, the calculated activation energies for the first and second reduction steps were 69 and 29 kJ/mol, respectively. While the former value is in good agreement with the activation energy obtained from the isothermal reduction of Ag 2 O to Ag, 64 kJ/ mol, the latter was found to be lower than the corresponding value for MoO 3 to MoO 2 under isothermal conditions, 124 kJ/mol. It was found that the presence of metallic silver obtained from the initial reduction step of Ag 2 MoO 4 not only lowers the energy barrier but the reducing temperature of the subsequent reaction steps (i.e., MoO 3 fi MoO 2 fi Mo).

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“…In addition to Fe 2 O 3 , both Fe 3 O 4 and FeO exist in the multiple reduction of iron ore beyond 843 K. However, whether MgO can react with Fe 3 O 4 or FeO to form a beneficial barrier to inhibit defluidization has not been reported. Actually, thermodynamic calculation predicted that both MgO · Fe 2 O 3 and MgO · FeO could form by the reactions of MgO with different iron oxides (Fe 2 O 3 , Fe 3 O 4 , and FeO) at typical fluidized bed reduction temperatures of 973–1173 K. Experimentally, reactions between MgO and iron oxides in diffusion couples were observed . However, because these studies mainly focused on the elements migration behavior during the iron ore sintering process, the annealing temperature of the diffusion couple was all set above 1363 K. Consequently, the role (physical barrier or chemical barrier) of MgO in preventing the defluidization of Fe 3 O 4 and FeO at typical fluidization temperatures remains unclear.…”

Section: Introductionmentioning

confidence: 99%

The Role of MgO Powder in Preventing Defluidization during Fluidized Bed Reduction of Fine Iron Ores with Different Iron Valences

Zhu

Yang

et al. 2016

steel research int.

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The role of MgO powder in preventing defluidization during the fluidized bed reduction of fine iron ores with different iron valences is investigated. The inhibiting effect of MgO powder on different types of fine iron ores is the same at 973 K, whereas it is sequenced as FeO > Fe 3 O 4 > Fe 2 O 3 at 1073 and 1173 K. Specific diffusion couples are employed to clarify the valence-dependent inhibiting mechanism. Electron probe microanalysis, X-ray diffraction results, and the estimation of diffusion activation energy indicate that the inhibiting effect of MgO powder on defluidization is mainly caused by the physical barrier effect for all iron oxides below 1073 K, while the defluidization prevention of Fe 3 O 4 and FeO at 1173 K is mainly attributed to the formation of Fe 2 MgO 4 and MgO Á FeO compounds on the surface, respectively. As a result, the required MgO content to prevent defluidization is sequenced as m(Fe 2 O 3 ) > m(Fe 3 O 4 ) > m(FeO) at 1173 K. Consequently, the MgO addition at the FeO stage will be more effective in preventing defluidization than the addition at Fe 2 O 3 and Fe 3 O 4 stages during multi-stage fluidized bed reduction of fine iron ores.

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A thermodynamic study of the molybdenum-oxygen system

Cited by 23 publications

References 21 publications

Thermodynamic evidence for phase transition in MoO2−δ

Thermodynamic evidence for phase transition in MoO2−δ

Reduction Kinetics of Ag2MoO4 by Hydrogen

The Role of MgO Powder in Preventing Defluidization during Fluidized Bed Reduction of Fine Iron Ores with Different Iron Valences

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