Molecular oriented domains (MOD) and their effect on technological parameters within the structure of cokes produced from binary and ternary coal blends

The aim of this work was to characterize molecular oriented domains in the cokes produced from binary and ternary blends of three bituminous Polish coals of varying carbon content: 82.7, 86.2 and 88.7 wt.% and, consequently, of different caking propensities of the Roga Index equal to 24, 63 and 77, respectively. The coals were collected from the Krupiński, Szczygłowice and Zofiówka mines, located in the Upper Silesian Coal Basin, Poland. They are commonly used in Polish coke‐making industry. The samples were studied using transmission electron microscopy (TEM) with the 002 dark field mode (002DF). As a result of these studies, an average area (SMOD) of molecular oriented domains (MOD) was determined for each sample. Values of the SMOD parameter are discussed in relation to the composition of the blends. A distinct relationship between the Zofiówka coal content in a blend and the microtexture ordering degree of the cokes was found: the higher the Zofiówka coal content in a blend, the higher the SMOD value. Values of SMOD were related to the other structural parameters, i.e., to the average height of graphite-like crystallites, Lc, and to the percentage contribution of ordered structures, obtained using XRD and Raman spectroscopy, respectively. The cokes containing 30–50% of the Zofiówka coal in a blend were found to have very well-ordered structures characterized by parameters close to those of the coke from the single Zofiówka coal reaching, dependently on a given factor, up to 80–99% of the values obtained for the coke from this strongly-caking coal. Values of SMOD were also related to the technological indices of the cokes studied. Generally, the highly organized microtexture of the coal blend cokes was found to affect the CRI index: the lower is the value of SMOD in the coke, the higher its CRI.

► Average MOD area depends on average crystal stacking.
► Sizes of MODs were found to increase with increasing content of very good coking coal.
► Highly organized microtexture of cokes affect technological indices CRI and CSR.