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10.2 Physicochemical Properties of Carbon Materials 271

is called rhombohedra1 graphite.The d(0 0 2) interplanar spacing in graphite is
0.3354 nm in the C-axis direction (perpendicular to the layer planes), while the
C–C bond distance in the A-axis direction (parallel to the layer planes) is 0.142 nm.
It is apparent in Figure 10.1a that graphite has two distinct surfaces present, the
basal plane and the edge sites. Furthermore, the physical properties of graphite
are highly anisotropic because of this crystallographic structure. For instance, the
electrical conductivity in the direction parallel to the basal plane is about 100 times
higher than in the perpendicular direction.
Amorphous carbons (see Figure 10.1b) also consist of hexagonal carbon rings,
but the number of these rings that constitutes a crystallite is much less than for
graphite. In addition there is very little order between the layers. Instead, the
layers are rotated with respect to each other, but they are parallel to each other
(i.e., the material is turbostratic) and there is no three-dimensional ordering. The
layer spacing of carbon blacks is typically >0.350 nm, and the crystallite sizes are
typically 1.0–2.0 nm for L a (crystallite size in the direction parallel to the basal
plane) and L c (crystallite size in the direction perpendicular to the basal plane). In
contrast, L a and L c for graphites can be >100 nm. The surface area of graphite and
2
amorphous carbon can be <10 to >l000 m g −1 respectively. The densities of these
carbonaceous materials are 2.25 g cm −3 for graphite and usually <1.80 g cm −3 for
amorphous carbon. Further details on the physical properties can be found in the
extensive discussion by Kinoshita [1] and in review articles [2–5].
The lattice plane images of carbonaceous materials, which were obtained by
high-resolution transmission electron microscopy (HRTEM), are reviewed by
Millward and Jefferson [6]. Examples of HRTEM of carbon blacks are presented
in Figure 10.2 to illustrate the difference in the structure of an amorphous carbon
and a graphitized carbon. The electron micrographs show a distinct difference
in the structure of the carbon particles. The amorphous carbon (d(002) spacing
of 0.352 nm) shows little evidence for long-range order of the basal planes. On
the other hand, the graphitized carbon black (d(0 0 2) spacing of 0.344 nm) has
well-defined layer planes that follow the surface contours of the carbon particles.
◦
Despite heat treatment at 2700 C, the d(0 0 2) spacing is much higher than that

(a) (b)
Figure 10.2 High-resolution transmission electron mi-
crographs of carbon black (Sterling R. Cabot Corp.):
(a) as-received and (b) heat-treated at 2700 C.
◦
Scale marker 10 nm.