Thermodynamic properties of the calcium ferrites CaFe2O4 and Ca2Fe2O5

Jacob, K. T. ; Dasgupta, N. ; Waseda, Y. (1999) Thermodynamic properties of the calcium ferrites CaFe2O4 and Ca2Fe2O5 Zeitschrift für Metallkunde, 90 (7). pp. 486-490. ISSN 0044-3093

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The chemical potentials of CaO in the two-phase fields Fe2O3 + CaFe2O4 and CaFe2O4 + Ca2Fe2O5 of the pseudobinary system CaO - Fe2O3 have been measured in the temperature range from 975 to 1275 K, relative to pure CaO as the reference state, using solid state galvanic cells incorporating single-crystal CaF2 as the solid electrolyte. The cell was operated under pure oxygen at ambient pressure. The standard Gibbs energies of formation of calcium ferrites, CaFe2O4 and Ca2Fe2O5, were derived from the reversible emfs. The results can be summarized by the following equations:CaO + Fe2O3 → CaFe2O4;Delta G degrees = - 37,480 + 1.16 T (+/- 250) J/mol 2 CaO + Fe2O3 → Ca2Fe2O5;Delta G degrees = - 45, 280 - 13.51 T (+/- 275) J/mol These values are compared with thermodynamic data reported in the literature. The results of this study are in excellent agreement with heat capacity data, and in reasonable agreement with earlier measurements of enthalpy and Gibbs energy of formation, but suggest significant revision of enthalpies of formation of calcium ferrites given in current thermodynamic compilations.

Item Type:Article
Source:Copyright of this article belongs to Carl Hanser Verlag.
ID Code:94983
Deposited On:10 Oct 2012 06:31
Last Modified:10 Oct 2012 06:31

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