Hitomi Hatano

Modification of synthetic mesophase pitch with iron oxide, Fe2O3

Abstract 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.

Improvement and control of the quality of binder pitch for graphite electrodes

Abstract Factors influencing the coke yield and the softening point (SP) of pitches were studied to ascertain procedures for the improvement and control of their quality. The coke yield of pitches from different tar sources is expressed as a linear function of the BI content. Pitches were prepared by distillation under constant operating conditions. The coke yields of pitches, determined by thermogravimetric analysis (TGA), increased with their benzene insoluble (BI) content, which is controlled by reflux heat treatment. Softening point increased with the nitrogen content as well as BI content. Therefore, increasing the BI content and decreasing the nitrogen content increases coke yield without any change in the softening point of binder pitches for graphite electrodes.