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

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: D f G q F e3 xVxO4 ( J/mol) = (1 x/2)D f G q F e3O4 + (x/2)D f G q F eV2O4 + (1 x/2)RTln( 1 x/2) + (x/2)RTln(x/2) 168627.48( 1 x/2)(x/2). [GRAPHICS]