Graphite crystals in blast furnace coke

Abstract

Graphite was found at several spots on the porous surface of a sample of blast furnace (BF) coke in association with droplets of Si-bearing iron and other inorganic compounds. It occurred in foliated intergrowths and rose-like aggregates of euhedral to subhedral crystals of various size (10 μm–0.7 mm) and morphologies, the generic forms that can be seen in the crystals being basal pinacoid, hexagonal prism and hexagonal dipyramid. The largest crystals have a flake-like habit and are represented by a combination of a basal pinacoid and a hexagonal prism. Graphite crystals that have an ideal hexagonal prism in their cross-section are rarer than distorted forms. There are twins on the dypiramidal composition planes and twins produced by rotation on [0 0 0 1]. The major deformations in the crystals, i.e. detaching, bending and rolling of (0 0 0 1) planes, may be referred to exfoliation phenomena caused by potassium and sodium from circulating BF gases and enforced by the BF gas flows. The formation of graphite crystals on a surface of BF coke, especially those of flake-like morphology with an undeveloped hexagonal prism, possibly decreases its reactivity and can be accompanied by the generation of fines. The graphitic coating on a surface of BF coke can act as a lubricant to facilitate coke pieces sliding over each other thus affecting the mechanical stability of the coke cone in a BF.