Microstructure of thermal conversion products of β resin from coal tar pitches

Three kinds of β resin (named as β-1, β-2, and β-3) were obtained with the method of secondary solvent extraction, hot filtering and distillation.In this process, the toluene and quinoline were used as the solvents, three typical types of pitches (medium pitch, thermal modified pitch, and oxidation modified pitch) were used as the raw materials.Elemental analyzer, TGA, and FTIR spectrum combined with curve-fitting method were used to study the basic physic properties of β resins.Three kinds of β resins based carbon (named as β-1-C₅₀₀-P, β-2-C₅₀₀-P, and β-3-C₅₀₀-P, respectively) were obtained using the methods of thermal conversion and carbonization process.Polarizing microscope, XRD and Raman spectrum combined with curve-fitting method were used to characterize the microstructure of the thermal conversion products.The results show that the fine fibrous structure and leaflet structure of β-1-C₅₀₀-P were 24.71% and 56.32%, respectively.The fine fibrous structure of β-2-C₅₀₀-P was 40.40%.However, the polarized microstructures of β-3-C₅₀₀-P were mainly composed of isotropic texture and mosaic texture.The contents of ordered carbon crystallite (Ig) of β-1-C₅₀₀-P and β-2-C₅₀₀-P were 78.78% and 82.43%, respectively.The crystallite sizes (Lc) of these two kinds carbon were 1.90 nm and 1.94 nm.However, the Ig and Lc of β-3-C₅₀₀-P were 53.17% and 1.58 nm respectively.The contents of ideal graphite microcrystalline (I_G/I_All) of β-1-C₅₀₀-P, β-2-C₅₀₀-P, and β-3-C₅₀₀-P were 10.13%, 10.46%, and 8.51% respectively.The contents of amorphous carbon (I_D3/I_All) were 10.94%, 10.48, and 11.55% in turn.The result of polarization microstructure is well correlated with the distribution of carbon crystallite (the results from XRD and Raman spectrum combined of curve-fitting method).