| Popis: |
Pyrolysis products produced from two pitch precursors, a petroleum pitch and a coal extract, have been characterized by broad line proton NMR and thermogravimetry. It is shown that the nmr technique is excellent for determining the glass transition temperature, Tg, of pitch and its pyrolysis residues and can also give useful information about the rates of the molecular processes that occur in the transition region. The glass transition temperature increases steadily with extent of pyrolysis, which is assessed from the volatile content and level of toluene insolubles. The kinetics of weight loss of each pyrolysis residue on further carbonization were also followed and apparent activation energies, Ea, determined. The value of Tg and Ea are considered to be largely determined by the amount of low molecular weight species in the pyrolysis residue such that when Tg is plotted against Ea, the data from both series superimpose. |
