Studies on Carbonization of Pitches (III)

Abstract

Influences Coustitutions of the starting pitches upon the structure and physical properties of the cokes obtained by carbonization at the temperatures of 400°-2, 500°C under a nitrogen flow were studied by means of polarized-light microscopy, measurement of coefficient of thermal expansion (C.T.E.) and x-ray diffraction to reveal factors which affect the formation of needle-like cokes.Coatar pitches and pitches obtained while thermal cracking of crude oil (Kureha pitches) were used to be fractionated with benzene and quinoline into three fractions of BS (benzene soluble), BI·QS (benzene insoluble-quinoline soluble), and QI (quinoline insoluble), which may have increased degrees of condensation in this order.BS from both pitches gave needle, like cokes via similar steps as reported previo-usly, whereas BI·QS which did not melt at carbonization temperatures up to 2.500°C similarly to QI formed non-graphitizing carbon of low crystallinity (Lc =50Å calcined at 2, 500°C). It is noted that addition of BS as low as 5 wt % into BI·QS converted the mixture pitches fusible at the early stage of carbonization and therefore gave needle-like cokes of high crystallinity (Lc=500Å calcined at 2, 500°) and orientation through steps of spherical body formation and their calescence. As far as the carbonization rate, BI-QS introduced into BS lowered the temperature of sphere bodys' appearance and accelerated their growth and coalescence in proportion with its amount. In addition, high orientation of cokes obtained from the mixture pitches of BS and BI·QS revealed by the microscopic observation was also ascertained by low CTE values comparable with or even better than those of cokes from BS.