Calorimetric study of the order-disorder transformations in graphite-halogens

The first determination of the enthalpy and entrophy of transformation for the order-disorder transformations in graphite intercalation compounds is reported here. By using differential scanning calorimetry, the order-disorder transformation associated with the intralayer intercalate position ordering has been observed at 375 ± 2 K in graphite-Br₂ and at 314 ± 2 K in graphite-ICl. The transformation temperatures show a strong dependence on the intercalate species but relatively little dependence on the intercalate concentration. The enthalpies of transformation are 108 ± 15 cal mol^-1 bromine and 460 ± 50 cal mol^-1 ICl for graphite-Br₂ and graphite-ICl respectively. Moreover, for graphite-Br₂ an endothermic peak at 277 ± 2 K has tentatively been identified with the order-disorder transformation associated with the intralayer intercalate molecular orientation ordering. The observed order-disorder transformations have all been found to be first-order transformations.