Atomic-scale understanding about coke carbon structural evolution by experimental characterization and ReaxFF molecular dynamics

Atomic-scale structural transformation of coke carbon in the thermal annealing process were investigated with 4 coke carbon samples using X-ray diffraction, Raman spectroscopy, X-ray photoemission spectroscopy, and ReaxFF molecular dynamics. Micro-crystal graphite was confirmed to be the basic structural unit in coke carbon structure, and its average size increased from (Lc: 23-27 A; La: 48-50 A) to (Lc: 53-78 A; La: 53-63 A) with increasing annealing temperature. The coke carbon structural evolution in 1300-1500 °C is not Raman-sensitive because most coke carbon boding type was found to be sp2 with a stable content (>60%). ReaxFF simulation repeated the experimental results very well and indicates that it is relatively hard to form a well structural order in the graphene plane (La) direction compared with that in the vertical direction (Lc). Five-membered carbon rings, especially when two five-membered rings connected together, make the graphene layers curved to some extents, leading to the formation of ...