Structural transformations during preparation of fine forms of exfoliated graphite

Abstract

Electron transmission microscopy and microdiffraction, X-ray phase analysis, electric conduction, and thermal-emf measurements are used to study the change in structural conditions of graphite bisulfate residual compounds (GBRC) in fine-grained exfoliated graphite with both free expansion and expansion within a closed volume. It is established that GBRC in all of the test temperature range (200–1000°C), including high-temperature rapid heating and with pressures of 5–20 MPa, in a structural respect are a heterogeneous system including graphite crystals areas of structure heterogeneity specified by the distribution of intercalate residues with a different degree of ordering, and also at least two intercalate residue phases of different fineness. Heating temperature, pressure, and the way of expansion govern the qualitative structure and quantitative ratio between various phase formations as well as the level of their disorder, i.e. the structural state of fine-grained exfoliated graphite. The effect of structural state on mechanical properties is studied by the method of repeated-static compression. It is shown that it is possible to obtain materials with prescribed mechanical properties by altering the structural state of fine-grained exfoliated graphite.