1996 Volume 82 Issue 5 Pages 419-424
Microtexture changes of semi-cokes produced from coking and slightly-coking coals were compared during the carbonization process in the temperature range of 600-1000°C, in order to correlate them with the mechanical strength development mechanism of cokes. The coke produced from Goonyella coking coal at a low temperature of 600°C exhibited a highly-oriented microtexture observed under the high resolution SEM, while the coke produced from Witbank slightly-coking coal at a higher temperature of 1000°C showed many plate-like edges on the surface. It is suggested that the microtexture of the cokes should reflect the fusibility and the caking properties of the original coals. The blending of the two coals was very influential on the carbonization behavior, the coking coal modifying the slightly-coking coal to produce the coke of high mechanical strength. The influences of cold moulding, coal blend ratios and heating rate during the carbonization on the properties of the cokes were also investigated in terms of the apparent density, the porosity, the tensile strength, and the microtexture of the cokes. The combination of the higher heating rate of 10°C/min with the cold moulding was very effective to produce the cokes of the high tensile strength with relatively low density from the coal blends rich in the slightly-coking coal. The tensile strength of the cokes is essentially related to the anisotropic region development and the microtexture orientation extents of the cokes after the resolidification around 600°C, being influenced by the formation of cracks through the calcination around 800°C with the shrinkage and the thermal expansion. The endothermic reactions such as dehydrogenative condensation and the enlargement of aromatic carbon planar stacking proceeded during the calcination around 900°C observed by the high temperature DSC, although such evidence was not definitely observed by Raman spectroscopy. X-ray diffraction showed the evidence for the enlargement of aromatic planar stacking of the coke produced from the coking coal at 1000 °C.
