handbook of carbon, graphite, diamond and fullerenes

154 Carbon, Graphite, Diamond, and Fullerenes
Laminar Structure. The laminar structure of pyrolytic graphite
consists of essentially parallel layers (or concentric shells if deposited on a
particle or fiber). It is shown in Fig. 7.7.
Both columnar and laminar structures are optically active to polarized
light and usually have similar physical properties.[10)[14]
Figure 7.7. Laminar structure of pyrolytic graphite, deposited on carbon filament
(Photograph courtesy of Jack Chin, La Costa, CA.)
3.3 Isotropic Structure
The other type of pyrolytic structure, isotropic carbon, has little
graphitic characteristic and essentially no optical activity .It is composed of
very fine grains without observable orientation and for this reason, it is
known as isotropic carbon rather than isotropic graphite. It is often obtained
in fluidized-bed deposition, possibly due to continuous surface regeneration
by the mechanical rubbing action of the bed. An isotropic structure,
observed by transmission electron microscopy, is shown in Fig. 7.8.[21)