Thermodynamic properties of molybdenum silicides by molten electrolyte EMF measurements

EMF measurements on silicon concentration cell were carried out using molten lithium silicate electrolyte in the temperature range 1305-1507 K. Using the EMF-temperature relations, the standard free energies of formation for Mo3Si, Mo5Si3 and MoSi2 have been obtained as functions of temperature: ΔfG° (Mo3Si) (kJ mol−1) = −122.1 + 0.0027T (K) ± 0.15, ΔfG° (Mo5Si3) (kJ mol−1) = −312.9 − 0.0064T (K) ± 0.26 and ΔfG° (MoSi2) (kJ mol−1) = −146.3 + 0.0096T (K) ± 0.22, respectively. Combining the results with thermodynamic data, the standard enthalpies of formation for these silicides at 298 K have been calculated as ΔfH° (Mo3Si, 298) (kJ mol−1) = −122.1 ± 6.0, ΔfH° (Mo5Si3, 298) (kJ mol−1) = −313.5 ± 12.0 and ΔfH° (MoSi2, 298) (kJ mol−1) = −135.8 ± 4.5, respectively.