Thermodynamic analyses of iron oxides redox reactions

Abstract

The thermochemical data of iron oxide redox reactions in various textbooks and handbooks are not consistent. To clarify such confusions, the elementary thermodynamic data of various iron oxides, carbon oxides, hydrogen and water vapor are used to calculate the changes of thermodynamic quantities such as enthalpy, entropy and Gibbs free energy of the redox reactions. The predominance area diagrams are then reconstructed according to the newly calculated Gibbs free energy changes. In order to fit the precise Gibbs free energy data, the constrained optimization method is adopted based on the mathematical modeling software Lingo 11. The reduction experiments are successfully carried out to verify the calculated eutectoid temperature. It is concluded with sixteen empirical thermodynamic equilibrium formulas and eight enthalpy values at 25°C for iron oxides reduced by CO and H2, and the eutectoid temperature of the three iron oxide phases is 576°C.