Determination of standard gibbs energies of formation of Fe 2 Mo 3 O 12 , Fe 2 Mo 3 O 8 , Fe 2 MoO 4 , and FeMoO 4 of th
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9/11/03
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Determination of Standard Gibbs Energies of Formation of Fe2Mo3O12, Fe2Mo3O8, Fe2MoO4, and FeMoO4 of the Fe-Mo-O Ternary System and Phase of the Fe-Mo Binary System by Electromotive Force Measurement Using a Y2O3-Stabilized ZrO2 Solid Electrolyte KOICHIRO KOYAMA, MASAO MORISHITA, TOMOHIRO HARADA, and NOBUYUKI MAEKAWA The standard Gibbs energies of formation of Fe2Mo3O12, Fe2Mo3O8, FeMoO4, and Fe2MoO4 of the Fe-Mo-O ternary system and the phase of the Fe-Mo binary system have been determined by measuring electromotive forces of galvanic cells having an Y2O3-stabilized ZrO2 solid electrolyte. The results are as follows: f G° (FeMoO4)/kJmol1 1053.5 0.2983 (T/K) 0.4 Temperature range: 1112 to 1339 K f G° (Fe2Mo3O8)/kJmol1 2347 0.6814 (T/K) 1 Temperature range: 1112 to 1339 K f G° (Fe2Mo3O12)/kJmol1 2993 0.9105 (T/K) 2 Temperature range: 1040 to 1145 K f G° (Fe0.58Mo0.42)/kJmol1 18.7 0.0117 (T/K) 0.1 Temperature range: 1162 to 1223 K fG° (Fe2MoO4)/kJmol1 1174 0.342 (T/K) 1 Temperature range: 1243 to 1466 K where the standard pressure is 1 bar (100 kPa).
I. INTRODUCTION
THE experimental determination of the Gibbs energies of the Fe-Mo-O system was attempted by Rezukhina and Kashina.[1] They determined the standard Gibbs energies of formation of Fe2Mo ( phase), Fe3Mo2 ( phase), and FeMoO3 in the temperature range from 1160 to 1366 K by the electromotive force measurement using a solid oxide electrolyte. However, two of the present authors have clarified in the previous article[2] that FeMoO3 and the phase of the Fe-Mo system do not exist in the temperature range where they measured electromotive forces. Kleykamp and Shauer[3]
KOICHIRO KOYAMA, Professor, and MASAO MORISHITA, Associate Professor, are with the Department of Materials Engineering, Graduate School of Engineering, Himeji Institute of Technology, Himeji 671-2201, Japan. Contact e-mail: [email protected] TOMOHIRO HARADA, formerly Graduate Student, Department of Materials Engineering, Graduate School of Engineering, Himeji Institute of Technology, is with Shin Caterpillar Mitubishi Ltd., Akashi 674-0074, Japan. NOBUYUKI MAEKAWA, formerly Graduate Student, Department of Materials Engineering, Graduate School of Engineering, Himeji Institute of Technology, is with Nihon Densan Ltd., Kyoto 615-0854, Japan. Manuscript submitted September 23, 2002. METALLURGICAL AND MATERIALS TRANSACTIONS B
determined the standard Gibbs energies of formation of Fe2Mo3O8, Fe2MoO4, and the phase in the temperature range from 1173 to 1273 K; they measured electromotive forces using a solid electrolyte, and derived three equations with four unknowns, that is, f G° (Fe2Mo3O8), f G° (Fe2MoO4), f G° (), and f G° (Fe-side solid solution), and then calculated one of the unknowns, i.e., f G° (Fe-side solid solution), by applying a simple regular solution model to the Fe-side solid solution, and finally solved the simultaneous equations. However, because the solubility of Mo in Fe reac
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