Thermal gravimetric analysis of graphite-bromine compounds

Thermal gravimetric analysis was applied for the first time to the study of graphite intercalation compounds. The gravimetric measurements were carried out on graphite-bromine compounds in the temperature range from room temperature to 140 °C. Intercalate desorption was found to be thermally activated. Its rate is anomalously high near the intralayer intercalate position order-disorder transformation temperature (100 °C) and the exfoliation temperature. This rate was also found to increase with increasing intercalate concentration. The mechanism of desorption depends on the intercalate concentration. At high intercalate concentrations, desorption appears to be dominated by a diffusion process and has an activation energy of 14 kcal (mol Br₂)^-1, in good agreement with the activation energy for the diffusion of bromine in graphite. As desorption ends, the intercalate concentration approaches a minimum value which depends on the desorption temperature. Much of the retained intercalate is ordered. Below the intralayer order-disorder transformation temperature an initially saturated graphite-bromine sample has a minimum concentration of 18 - 19 wt.% Br₂. Above the order-disorder transformation temperature the minimum concentration is smaller. The energy of the desorption process is utilized mainly for the vaporization of the intercalate, as suggested by our differential scanning calorimetry results.