THE DEVELOPMENT OF MESOPHASE IN COAL-TAR AND PETROLEUM PITCHES CHARACTERIZED BY EXTROGRAPHY

A series of three coal tar and two petroleum pitches were characterized in terms of chemical composition by extrography combined with FT-i.r., g.c. and g.p.c. These pitches, along with another five pitches, were pyrolysed/carbonized isothermally at 425, 450 and 475-degrees-C for residence times of up to 180 min. Extents of mesophase formation, and size of mesophase growth units, were determined using an image-analysis system. Extents of formation of mesophase together with its characterization in terms of temperature and residence time are related to the extrography data. The process of homogeneous nucleation of mesophase from a pyrolysing system is described in detail, together with a discussion of the different growth mechanisms of mesophase. The 10 pitches represent a wide range of rates of growth of mesophase, 9PP being the slowest, 8CTP being the fastest, with the eight coal tar pitches being intermediate. These phenomena are discussed in terms of the obtained chemical analyses and of influences of primary QI materials within the coal tar pitches.