Graphite: Flat, Fibrous and Spherical

Abstract

The paradigm for the structure of graphite is that of a staggered stacking of flat layers of carbon atoms (Figure 6-1). Individual layers, sometimes referred to as graphene sheets,¹ are weakly bonded to each other and are composed of strongly bonded carbon atoms at the vertices of a network of regular hexagons in a honeycomb pattern.² Both the properties and the morphology of graphite reflect its highly anisotropic structure. Due to the strong bonding within layers and the weak bonding between layers, the growth of graphite takes place predominantly along the edges of the layers (perpendicular to the c axis) and only very slowly normal to the layers (parallel to the c axis). As a result of the growth rate anisotropy, the anisotropic surface energy, and the crystallographic symmetry, the expected morphology for graphite crystals is that of tabular hexagonal prisms.³ However, well-formed natural crystals, such as shown in Figure 6-2, are rare,⁴ and it has been said that near-ideal crystals of graphite may be rarer than diamonds.⁵ Well-formed, laboratory-grown crystals of graphite are also uncommon. During the 1960s, graphite crystals from Ticonderoga, New York, and Sterling Hill, New Jersey, became a standard of perfection for experiments and for comparison with laboratory-grown crystals.^6,7