The Formation of Microstructure in Graphitizable Carbons.

摘要

The review focuses on progress made in the last decade in understanding the structural mechanisms involved in the formation of microstructure during the pyrolysis of graphitizable materials. The principal microstructural features are established in the final stages of liquid-phase pyrolysis after the carbonizing mass has transformed into a nematic liquid crystal,the carbonaceous mesophase,in which large aromatic layer molecules are aligned parallel in a lamelliform morphology but without the constraint of crystalline registry between the layers. The formation of the carbonaceous mesophase,usually near 450C,is essential to the thermal graphitizability of an organic precursor. In contrast to the three-dimensional crystal grains of most ceramic and metallic materials,the two-dimensional mesophase lamellae constitute the fundamental structural element of graphitizable carbons,and the filling of space by these flexible lamellae accounts for the characteristic bends,folds, splays,and lamellar stacking defects (disclinations) which are frozen into the microstructure as the mesophase congeals. (Modified author abstract)