Experimental Determination of the Standard Gibbs Energy of Formation of Fe_3–xV_xO₄ at 1473 K

Abstract

In the present study, an approach of determining the standard Gibbs energy of formation of Fe3–xVxO4 was proposed firstly, then the standard Gibbs energies of formation of a variety of Fe3–xVxO4 were determined experimentally, and finally, a calculating model of the standard Gibbs energy of formation of Fe3–xVxO4 was established. The detailed results are as follows: (1) the standard Gibbs energy of formation of Fe3–xVxO4 can be determined successfully by two steps; the first is to measure the chemical potential of Fe in Fe3–xVxO4 under fixed oxygen partial pressure, the second is to derive the chemical potential of V in Fe3–xVxO4 by Gibbs–Duhem relation; (2) the standard Gibbs energies of formation of Fe3–xVxO4 are mainly decided by the Fe/V molar ratio, and almost not influenced by the oxygen partial pressure in the range from 2.39 × 10−12 to 3.83 × 10−11 atm; (3) in this oxygen partial pressure range, the standard Gibbs energies of formation of Fe3–xVxO4 can be calculated satisfactorily by the following model: ΔfGFe3−xVxO4θJ/mol=1−x/2ΔfGFe3O4θ+x/2ΔfGFeV2O4θ+1−x/2RTln1−x/2+x/2RTlnx/2 − 168627.481−x/2x/2.

Keywords

• Fe_3–xV_xO₄
• Gibbs energy
• measurement
• modeling
• Gibbs–Duhem relation