Development of ordered structures in the high-temperature (HT) cokes from binary and ternary coal blends studied by means of x-ray diffraction and Raman spectroscopy

The aim of this work was to characterize ordered structures within cokes produced from single bituminous coals and from their blends. Three Polish coals of varying rank and caking ability were collected from the Krupiński, Szczygłowice, and Zofiówka mines, respectively. These coals were used for preparation of 19 blends: single (trivial blends), binary, and ternary ones. Cokes were manufactured in a laboratory scale using an apparatus with a Jenkners retort with a charge of 1000 g and heat-treatment temperature of 1000 °C. The X-ray diffraction (XRD) and Raman spectroscopy were used for the study. To determine the kind and size of ordered structures, the following parameters were discussed: interlayer spacing, d₀₀₂, crystallite stack height, L_c, obtained from the XRD studies as well as the fractional contribution of ordered elements to all kinds of structures, and ratio of the amount of graphite structures (G type) to the amount of D ₂-type structures (less ordered than graphite), determined with Raman spectroscopy. The cokes produced from blends were treated as a compound system dependent upon properties of its components, single coal cokes. Additivity of the structural parameters of the cokes from blends was verified by the series model. Well-ordered structures, including the graphite-like ones, were found in all cokes studied. The highest degree of ordering was found in the single coke from very good caking Zofiówka coal. A similar structure was found in the cokes from binary and ternary blends of medium content of this coal of about 30-50 wt %. The preparation of cokes with well-ordered structures from blends of considerable lower concentration of the Zofiówka coal is promising, because the cost of these coke productions is lower than that of single coke from the Zofiówka coal. Discrepancy between the experimental data and those obtained from the series model confirmed mutual interactions between coals in a blend that affects forming of well-ordered structures in the cokes. This interaction was found to be the strongest in the blends with the content of the Zofiówka coal equal to 30-50 wt %.