Modification of synthetic mesophase pitch with iron oxide, Fe_2O_3

摘要

Iron oxide (Fe_2O_3) was examined as an additive to improve the yield of the insoluble fraction in the synthetic mesophase pitch and to inhibit the expansion of the pitch during the heat-treatment and the successive carbonization of the insoluble fraction. The pitch was heat-treated at 350degC for 4 h under 500 rev./min stirring by adding 0,6, 17, and 25 wt. Fe_2O_3. The heat-treated pitch without additive produced swollen semi-coke with the flow domain texture whereas the heat-treated pitch with Fe_2O_3 produced porous but non-swollen semi-coke with the mosaic texture. Fe_2O_3 increased the yield of pyridine insoluble (PI) in the heat-treated pitch and inhibited completely swelling of the extracted insoluble fraction at its carbonization. The iron oxide is believed to enhance the oxidative polymerization of the lighter fraction in the pitch and to allow smooth liberation of evolving gases to suppress the expansion of the pitch and its PI during the carbonization. The successive calcination and graphitization gave spherical powders of the graphite. According to X-ray diffraction, Fe_2O_3 was transformed into Fe_3O_4, and then to elemental Fe and Fe3C by calcination at 1000degC. At the graphitization stage, elemental Fe was only present in the carbon, catalyzing the graphitization to a limited extent.