The vacuum residue of petroleum is cracked by coking at 500 ～ 550 ℃ to produce black solid coke. Its appearance is a black or dark gray honeycomb structure, and the pores in the coke block are mostly oval and interpenetrating.
It is generally considered to be an amorphous carbon body; or a highly aromatized polymer carbide that contains fine graphite crystals in a needle-like or granular structure. The carbon-hydrogen ratio is high, ranging from 18 to 24. Relative density is 0.9 ～ 1.1, ash content is 0.1% ～ 1.2%, volatile matter is 3% ～ 16%.
