Exfoliation of intercalated graphite

By X-ray diffraction, exfoliated graphite-Br₂ was found to exhibit the same in-plane superlattice ordering as intercalated graphite prior to exfoliation. This ordering persisted even after heating for 1 hr at 1700°C. By dilatometry, a single exfoliation event was found to consist of multiple expansion spurts, which occurred at ~ 150 and ~ 240°C for the first exfoliation, and ~ 100 and ~ 240°C for subsequent cycles. The amount of expansion was found to increase with decreasing intercalate activity during intercalation. With exfoliation cycles to higher temperatures or longer times, the amount of residual expansion after the collapse on cooling increased until no second exfoliation was observed or reheating. Due to intercalate desorption, the amount of expansion for concentrated samples increased with increasing sample width; desorbed samples showed little width dependence. Acoustic emission was observed before appreciable expansion during the first exfoliation cycle; it was not observed during the collapse or subsequent exfoliation cycles. A model of exfoliation involving intercalate islands is proposed.