Fabrication of Binder Pitches Allowing for Low-Temperature Formation and High Coking Values and Examination of Mechanical Properties of Artificial Graphite Blocks Made of Binder Pitches.

The present study focused on the development of a binder pitch to allow for low-temperature forming processes when fabricating coke-based artificial graphite blocks while increasing the density of the resultant blocks. To this end, high-softening-point (200 °C) pitches were fabricated. The pitch and byproducts obtained from the pitch synthesis were then used as binders to fabricate blocks with high mechanical strength and low porosity. Pitches were fabricated using pyrolyzed fuel oil (PFO), a petroleum residue. A high-softening-point (200 °C) pitch synthesized at 420 °C for 3 h was used as a binder pitch, and conventional pitch (124 °C) was synthesized at 400 °C for 1 h and then used. Pitch byproducts were extracted according to the boiling point of naphthalene (two rings) and anthracene (three rings) with varying numbers of aromatic rings by distillation. The largest amount of pitch byproduct was obtained in the temperature range from 220 to 340 °C, and the content of naphthalene in the byproduct was the highest over the entire temperature range. The fabricated pitches at 420 °C and byproducts were mixed to form modified pitches. It was found that their softening point and coking value (CV) decreased with the increasing content of the pitch byproduct. Low-boiling point components of the byproducts were removed from the modified pitches at the kneading process temperature (200 °C), and the mass-loss rate observed in the carbonization process temperature range (200-900 °C) was comparable to that of the high-softening-point pitch. The kneading rate of the pitch and byproduct was determined and selected based on the mass-loss rate described above, and blocks were then fabricated using a hot press. Subsequently, the fabricated blocks were subjected to heat treatment for carbonization (900 °C) and graphitization (2700 °C). After the heat treatment, the true density and apparent density of the blocks were measured, and the porosity of the blocks was calculated based on these values. The porosity of the graphite block fabricated using the pitch with a softening point of 120 °C was 21.84%, while the porosity of the graphite block fabricated using the modified pitch was 14.9%. For mechanical strength analysis, their compressive strength was measured. The compressive strength of the graphite block made of the conventional pitch (CP) was measured to be 47.59 MPa, while the compressive strength of the graphite block made of pitch mixed with a byproduct distilled at 220-340 °C was 58.79 MPa. This result suggested that a decrease in the porosity resulted in increased mechanical strength. The application of the modified pitches developed in the present study temporarily decreased the softening point of the high-softening-point pitch due to the effect of the added byproducts, allowing for a low-temperature forming process. It was also possible to fabricate artificial graphite blocks with low porosity due to the high CV of the high-softening-point pitch. As a result, blocks with high mechanical strength could be obtained.