Microstructure and stability of iron chloride graphites

Abstract

Two methods have been used to prepare iron chloride intercalates of natural graphite. Ferric chloride intercalates are demonstrated to be both extremely air sensitive and also to undergo gradual physical and chemical changes upon storage, solvent treatment, heating and washing. Gradual interconversion to higher staging or direct de-intercalation are the two observed reaction pathways. The ferrous chloride intercalates (obtained by H₂ reduction) are found to be even more air sensitive than their ferric precursors, decomposing to yield disordered graphite and crystalline iron chloride hydrates and oxyhydrates. The Mössbauer spectrum of FeCl₃ graphite was found to consist of two singlets (δ₁= 0.47 mm s^–1 and δ₂= 0.61 mm s^–1), giving rise to two different quadrupole doublets in the FeCl₂ intercalate. High-resolution transmission electron microscopy confirms earlier results and regular first-stage intercalate is imaged for the first time. The discussion of the results is based on an island-structured intercalate and a stabilising influence of chemisorbed Cl₂ and/or HCl. The limitations of different techniques to the study of graphite intercalates (including Mössbauer spectroscopy, X-ray powder diffraction, thermogravimetric analysis, weight-uptake measurements and electron microscopy) are discussed.