Preferred Label : carbonaceous mesophase;
IUPAC definition : A liquid-crystalline state of pitch which shows the optical birefringence of disc-like
(discotic) nematic liquid crystals. It can be formed as an intermediate phase during
thermolysis (pyrolysis) of an isotropic molten pitch or by precipitation from pitch
fractions prepared by selective extraction. Generally, the spherical mesophase precipitated
from a pyrolysing pitch has the Brooks and Taylor structure. With continuous heat
treatment the carbonaceous mesophase coalesces to a state of bulk mesophase before
solidification to green coke with further loss of hydrogen or low-molecular-weight
compounds.;
Scope note : in the formation of carbonaceous mesophase by thermolysis (pyrolysis) of isotropic
molten pitch, the development of a liquid-crystalline phase is accompanied by simultaneous
aromatic polymerization reactions. the reactivity of pitch with increasing heat treatment
temperature and its thermosetting nature are responsible for the lack of a true reversible
thermotropic phase transition for the bulk mesophase in most pitches. due to its glass-like
nature most of the liquid-crystalline characteristics are retained in the super-cooled
solid state.;
Origin ID : C00822;
See also
A liquid-crystalline state of pitch which shows the optical birefringence of disc-like
(discotic) nematic liquid crystals. It can be formed as an intermediate phase during
thermolysis (pyrolysis) of an isotropic molten pitch or by precipitation from pitch
fractions prepared by selective extraction. Generally, the spherical mesophase precipitated
from a pyrolysing pitch has the Brooks and Taylor structure. With continuous heat
treatment the carbonaceous mesophase coalesces to a state of bulk mesophase before
solidification to green coke with further loss of hydrogen or low-molecular-weight
compounds.
