Importance of mineralogical data for influencing properties of coke : a reference on SiO2 polymorphs

• Published in: Steel research international 2006-11, Vol.77 (11), p.770-773
• Main Authors: GORNOSTAYEV, Stanislav S, KERKKONEN, Olavi, HÄRKKI, Jouko J
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Metals. Metallurgy
• ISSN: 1611-3683; 1869-344X
• DOI: 10.1002/srin.200606461

SiO2 occurs in coking coals as pure quartz and also in complex aluminosilicates. At coking temperatures, pure SiO2 has several polymorphs (alpha- and beta-quartz and beta-tridymite) and transformations from one to another are accompanied by volume changes in the mineral matter that can lead to the formation of cavities and cracks in a coke matrix. These can weaken the coke physical strength and lead to a higher circulation of gases within the pieces. The grain size of the primary quartz crystals in a coal blend is also important for the estimation of coke strength: the larger the crystals that occur in a coal, the larger the cavities and cracks that will ensue (weaker coke). The occurrence of any given SiO2 polymorph indicates the temperature of its formation and can be used to correlate other changes in coke-forming compounds with certain temperatures. A high amount of free quartz in a coal blend can be considered a negative factor for coking. For a better understanding of the influence of bulk SiO2 on coke quality, mineralogical (phase) analysis and quartz grain size measurements on coking coals can be helpful. Under the blast furnace conditions, SiO2 polymorphs have no substantial influence on the coke physical strength.