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Electrochemical Determination of the Gibbs Energy of Formation of Na 2 Fe 2 O 4 and Na 3 Fe 5 O 9 Employing Na‐β‐Al 2 O 3 Solid Electrolyte
Author(s) -
Kale Girish Madhav,
Srikanth Srinivasan
Publication year - 2000
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.2000.tb01167.x
Subject(s) - electromotive force , gibbs free energy , emf measurement , analytical chemistry (journal) , isothermal process , electrochemistry , electrolyte , chemistry , solid solution , electrochemical cell , crystallography , thermodynamics , electrode , physics , organic chemistry , quantum mechanics , chromatography
The results of isothermal equilibration and X‐ray diffraction studies in Fe 2 O 3 ‐rich compositions of the Na 2 Fe 2 O 4 –Fe 2 O 3 pseudo‐binary system suggests the coexistence of an equilibrium between α‐Na 2 Fe 2 O 4 and Fe 2 O 3 at low temperatures (923–1023 K) and Na 3 Fe 5 O 9 and α‐Fe 2 O 3 at higher temperatures (>1023 K). The Gibbs energy of formation for the interoxide compounds Na 2 Fe 2 O 4 and Na 3 Fe 5 O 9 has been measured using solid‐state electrochemical cells that use Na‐β‐Al 2 O 3 as the solid electrolyte. The electromotive force (emf) measurements are performed on cell I, which can be described asand cell II, which can be described asThe temperature dependence of the steady‐state emf of cells I and II can be represented aswith a standard error of ±5 mV for each emf measurement. By combining the measured emf values of cells I and II with the activity of Na 2 O in α‐Al 2 O 3 + Na‐β‐Al 2 O 3 from the literature, the computed Gibbs energy of formation of Na 2 Fe 2 O 4 and Na 3 Fe 5 O 9 from solid Na 2 O and α‐Fe 2 O 3 can be expressed aswhere the standard error is ±5500 J/mol for each ΔG° measurement. These uncertainty limits are due to the combined errors in the emf measurement and the thermodynamic data of the reference electrode material that have been used in the present study.