The formation of graphitizing carbons from the liquid phase

Abstract

The formation of graphitizing low-temperature carbons by solidification from a liquid phase proceeds via the separation of a mesophase having properties similar to those of liquid crystals. Initially, the mesophase, consisting of planar aromatic compounds of high molecular weight, separates in the isotropic liquid as spherical droplets having a considerable degree of molecular order, with the aromatic sheets stacked in parallel array. The sheets are arranged perpendicularly along one diameter of a sphere, but are curved so that they are normal to the surface. On prolonged heating the spheres coalesce and extended regions of uniform orientation may be formed; eventually a solid semi-coke is obtained. It is the generally lamellar arrangement of the molecular structure in these regions which favours the formation of graphite carbon at high temperatures. When isolated spheres are heated to graphitizing temperatures contraction occurs in the direction perpendicular to the preferred orientation. The bodies become elliptical in section and each is converted to a mass of small graphite crystals.