Modification of synthetic mesophase pitch with iron oxide, Fe₂O₃

Iron oxide (Fe₂O₃) 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 350°C for 4 h under 500 rev./min stirring by adding 0, 6, 17, and 25 wt.% Fe₂O₃. The heat-treated pitch without additive produced swollen semi-coke with the flow domain texture whereas the heat-treated pitch with Fe₂O₃ produced porous but non-swollen semi-coke with the mosaic texture. Fe₂O₃ 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, Fe₂O₃ was transformed into Fe₃O₄, and then to elemental Fe and Fe₃C by calcination at 1000°C. At the graphitization stage, elemental Fe was only present in the carbon, catalyzing the graphitization to a limited extent.