FREE-ENERGY OF FORMATION OF GEO2(HEX) BY EMF-MEASUREMENTS

The values of the standard free energy of formation ΔfG0m of the stable tetragonal form of GeO2 as well as of the metastable hexagonal modification were obtained from e.m.f. measurements on the following types of cells* * 1 atm = 0.1013 MPa.. Pt, C, Ge, GeO2(tet)/15 wt.% Y2O3ZrO2/inert gas (Po≈ 10-4atm), Pt and Pt, C, Ge, GeO2(hex)/15 wt.% Y2O3ZrO2/inert gas (Po ≈ 10-4atm), Pt The e.m.f. data yielded the following least-squares expressions. ΔF0m (GeO2, hex) ± 1.2 kJ-1 = -549.86 + 0.16837 T (810-1180K) Δ0m (GeO2, tet) ± 1.15 kJ-1 = - 571.39 + 0.18657 T (800 -1150 K) Combining the data for GeO2(hex) with calorimetric data, a value of - 559.7 ± 0.9 kJ was obtained for ΔfH0m(GeO2, hex, 298 K) from a third law plot. The transformation from GeO2(tet) to GeO2(hex) had an enthalpy value of - 21.5 kJ at 1176 K. © 1979.