Characterisation of a basal-plane-oriented graphite

Abstract

We have employed scanning electron microscopy (SEM), scanning tunnelling microscopy (STM), wide-angle X-ray scattering (WAXS), small-angle neutron scattering (SANS) and adsorption isotherms to characterise the recompressed, exfoliated graphite ‘Papyex’. The substrate is found to consist of ca. 60% void space, most of which is associated with galleries with a thickness of ca. 300 Å. The substrate contains ca. 70% rhombohedral and 30% hexagonal graphite crystallites with dimensions of the order of several hundred angstroms. We confirm that Papyex has preferentially oriented graphite (0001) planes whose surfaces mainly contribute to the total available surface area. Using the theory of Debye etal., the substrate may be classed as a random two-phase structure. SANS experiments employing contrast variation show that the voids in Papyex are connected and fillable. A Guinier analysis is inappropriate to apply to the present system owing to the large scale and interconnected nature of the void space of the galleries. BET analysis shows Papyex is a non-porous or macroporous material giving a Type II isotherm with a surface area of ca. 20 g⁻¹ and negligible micropores. This suggests that the substrate consists of voids and macroscopic cracks and fissures with dimensions of the order of ca. 500 Å or more. Porod analysis of the SANS data gives a surface dimension of 2.5 and a surface area comparable to that obtained from the BET analysis. However, the limited range in which power-law behaviour is observed makes conclusions about fractal dimensions and polydispersity questionable.