Mass-spectrometric study of vaporization of FeCl3-graphite intercalation compound

The vaporization of stage 2 FeCl3-graphite intercalation compound (GIC) has been studied by a mass-spectrometric Knudsen effusion method in the temperature range 440-496 K, and compared with that of pure FeCl3(s). The main vapor species over pure FeCl3(s) are Fe2Cl6(g) and Cl-2(g), but over stage 2 FeCl3-GIC, the vapor species FeCl3(g) is identified in addition to Fe2Cl6(g) and Cl-2(g). Partial pressures of FeCl3(g), Fe2Cl6(g) and Cl-2(g) in equilibrium with stage 2 FeCl3-GIC are much lower than the corresponding pressures over pure FeCl3(s). On the basis of the equilibrium partial pressures over FeCl3-GIC, the enthalpies of reaction for the transition of stage 2 to stage 3 FeCl3-GIC by the vaporization of FeCl3(g) and Fe2Cl6(g) are evaluated to be (184.7 +/- 7.9) and (215.7 +/- 2.9) kJ mol(-1), respectively, and the enthalpy of reaction for the reduction of FeCl3 to FeCl2 in FeCl3-GIC to be (137.4 +/- 3.3) kJ mol(-1). The chemical activities of the FeCl3 and FeCl2 components in stage 2 FeCl3-GIC are determined to be 2 x 10(-3) and 5 x 10(-2), respectively, at 500 K.