The influence of oxidation upon strength and structure of a needle-coke and a coal extract coke

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Calcined commercial needle-cokes and coal extract coke are characterised by optical microscopy of polished surfaces. The needle-coke has an optical texture of coarse-grained mosaic, flow domain and a acicular flow domain; the coal extract coke has an optical texture of medium- and coarse-grained mosaics. The cokes are oxidised in air to 1–25% wt. loss. The microstrengths of original and oxidised cokes are measured. For the needle-cokes, a 1% wt. loss significantly reduces the microstrength values whereas for the coal extract coke the microstrength begins to decrease only after 15% wt. loss. SEM examination of original and oxidised surfaces indicates that oxidation of the needle-coke proceeds by the development of microfissures within the flow domain and by pitting of surfaces of the basal planes of the acicular flow domains. The surfaces of the coal extract coke were uniformly pitted. The decline of microstrength values of needle-cokes is associated with internal oxidation of the coke particles.