Thermodynamic properties of ZrMo2O8(s) and HfMo2O8(s)

Abstract

The standard molar Gibbs energies of formation of AMo2O8(s) (where A  Zr, Hf) have been determined using a solid oxide galvanic cell. The dependence of e.m.f. on temperature of the cell Pt/ZrMo2O8(s)+MoO2(s)+ZrO2(s)/CSZ/air/Pt could be represented by E(V) ± 0.001 ± 0.7276 − 2.749×10 1T(K) (870.5≤T(K)≤1159). Similarly the e.m.f. of the cell Pt/HfMo2O8(s) + MoO2(s) + HfO2(s)/CSZ/air/Pt could be represented by E(V)±0.001 0.7375−2.801×10 4T(K) (906≤T(K)≤1148). In these cells CSZ represents 15 mol% calcia stabilized zirconia solid solution. The calculated ΔfGm0(T) values for ZrMo2O8(s) and HfMo2O8(s) can be given by ΔfGm0(ZrMo2O8sT)(kJ mol1) ± 4.8 = −2535.4 + 0.6247T(K) ΔfGm0(HfMo2O8s.T)(kJ mol 1) ± 5.2 = −2551.4+0.6128T(K). ΔfHm0(298.15 K) of HfMo2O8(s) and ZrMo2O8(s) are calculated by the second-law method using the heat capacity values and can be given respectively as −(2568.3±2.0) and −(2588.6±2.2) kJ mol−1. The standard molar Gibbs energy of formation of MoO2(s) required for the calculations has also been determined using the e.m.f. technique.