Expansion of tetrachloroaluminate-graphite intercalation compound by reaction with anhydrous hydrogen fluoride

Abstract

Reaction of the stage-1 graphite tetrachloroaluminate intercalation compound prepared from highly oriented pyrolytic graphite with anhydrous HF yields expanded graphite. According to scanning electron microscopy, exfoliation of graphite layers occurs more intensely as the reaction temperature increases. X-ray diffraction shows the expanded graphite has low crystallinity and the layer structure of graphite is highly disordered. X-ray photoelectron spectroscopy confirms formation of AlF3 and absence of Cl and covalent C–F bonds. Infrared spectroscopy reveals the gaseous species released during the expansion are HCl and CF_4. These observations suggest the following reaction is the source of the expansion: CxAlCl_4(s)+4HF_l→(x-0.25)C(s)+AlF_3(s)+4HCl(g)+0.25CF_4(g).