Effect of expansion time on the microstructure of an expanded natural flake graphite

The changes of bulk density,specific surface area and microstructure of natural flake graphite after several expansions were studied by nitrogen adsorption,XRD and SEM.Results show that the differences in bulk density get smaller and smaller with increasing expansion time.The increase of specific surface area in the first expansion is much bigger than in following expansions.The lattice parameters of the graphite change very(slightly),with d_(004) and d_(101) increasing by only about 0.2 % and 0.4 % respectively after five expansions.SEM images show that the expanded graphite appears like crumpled paper in an expanded state.