Fine structure of coke received from coal tar pitch oxidized on the graphite foam surface

The paper presents the research results of the fine structure of coke which was received on the basis of coal tar pitch after oxidation in thin layers on the surface of graphite foam bubble walls. After oxidation the mixture of expanded graphite and pitch (8%) was milled, and workpieces obtained from powder were baked and gained the density of 1.5 g/cm3 due to shrinkage. The thickness of bubble walls is 5 nm, the thickness of pitch coke layers between bubble walls is one order of magnitude greater. The fine structure of coke was examined by X-ray diffraction and transmission electron microscopy. Peaks of 002 lines, narrow for the graphite foam and broad for the baked coke, show that the material consists of two phases, the coke 002 line is broadened towards small angles. Coke structure in baked workpieces is formed by single graphite-like layers of limited sizes. Separate layers are curved and form a polydisperse fullerene-like and closed globular structure with a globule size up to 20 nm. Pitch coke layers and bubble walls are sintered without cracking. Sequences of onion-like multilayer structures of up to 5 nm were detected on the wall surface of the graphite foam bubbles. The mechanism of oxidized pitch degradation during the formation of globular non-graphitized structures was suggested. During coking aromatic molecules of adjacent layers are joined by carbon-carbon chemical bonds in curved graphite-like layers. Curving of the graphite-like layers synthesized near the walls is possible in the direction from bubble walls thus leading to the formation of onion-like structures.