CARBONS FROM PYROLYSIS OF PITCHES, COALS, AND THEIR BLENDS

A review of chemical and physical factors influencing the growth, coalescence and final structures of mesophases from pitches and coals is presented. Definitions of carbon forms in common use are given. An explanation of mesophase as a nematic liquid crystal is put forward together with an account of its discovery. The phenomena of observation, growth and coalescence of mesophase are described leading to an explanation of the homogeneous nucleation of mesophase from liquid pitch and coal-melts. Structure within mesophase is outlined in terms of stacking of the constituent lamellar molecules. The optical texture (structure) of a coke is a function of the chemical composition and viscosity of the parent pyrolysis system, the intermolecular reactivities being of major importance. The role of hydrogen shuttling reactions in influencing sizes of optical texture is emphasized. The requirements of metallurgical coke are set out and related to coal science and technology. Major differences between the pyrolysis chemistry of pitches and coals are explained incorporating aspects of non-Newtonian behaviour of coal-melts. Mechanisms are summarized of interactions of coal blends with pitches and preheating is referred to. The Coking Capacity of a blend is elucidated.