Mesophase of Graphitizable Carbons

Abstract

Carbon materials are classified as being graphitizable or nongraphitizable. Nongraphitizable carbons are produced from such nonfusing materials as wood, nut-shell, carbons from highly cross-linkaged polymers (e.g., cellulose), thermosetting resins (e.g., poly(furfuryl)alcohol), and nonusing coals. The macromolecular skeletal structure of these materials remains during heat treatment (pyrolysis) because only small molecules are lost during pyrolysis. Resultant carbons are characterized by isotropic properties, high microporosity, and surface areas in the range 500–1500 m2 g−1. On the other hand, graphitizable carbons are formed from parent materials, e.g., pitches from petroleum and coal, which pass through a fluid stage during pyrolysis (carbonization). This fluidity facilitates the appropriate molecular mobility of the aromatic molecules of the system, resulting in intermolecular dehydrogenative polymerization reactions to create aromatic, lamellar (disc-like) molecules of size 200–1000 amu. These molecules ``associate'' to create a new liquid crystal phase, the so-called mesophase. A fluid phase is the dominant requirement for the production of graphitizable carbons. Definitions for carbon materials have been published in 1982 and 1983 [1].