Thermodynamic properties of FeCl3-graphite intercalation compounds by mass-spectrometric Knudsen effusion method

A mass spectrometric Knudsen effusion method has been used for the determination of thermodynamic properties of stage 1 FeCl3-graphite intercalation compound (GIC). Enthalpies of the transformation of stage 1 to stage 2 FeCl3-GIC by the vaporization of FeCl3 (g) and Fe2Cl6 (g), and enthalpy of the reduction of FeCl3 to FeCl2 in the stage 1 FeCl3-GIC have been determined to be 170.5±5.4, 188.2±5.4 and 144.5±4.9 kJ mol-1, respectively, from the equilibrium partial pressures over the GIC. Activities of FeCl3 and FeCl2 components in. the stage 1 FeCl3-GIC together with the activity coefficient of FeCl3 have been also evaluated. The activity coefficient of FeCl3 in the stage 1 FeCl3-GIC is found to be larger than that in the stage 2 FeCl3-GIC, indicating that the stage 1 FeCl3-GIC is thermodynamically less stable than the stage 2 FeCl3-GIC.