Spinel crystals in tuyere coke
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The amount and nature of the mineral phases in metallurgical coke can be regarded as important factors affecting its properties and behavior in the blast furnace (BF).[1,2] Data on the mineral phases in BF coke are still scarce, however,[2–5] and their behavior during coke degradation is still poorly understood. Under natural conditions, the composition, morphology, and textures preserve a record of the means by which the minerals were formed, and these data can be used to estimate the conditions of formation of their synthetic analogues,[6] including those originating in coking processes and during the evolution of coke in the BF. The changes that take place in the mineral phases of BF coke can be regarded as either structural or chemical.[2] The structural changes in particular include[2] expansion of metaclays and the swelling and balling-up of aluminosilicates, while the chemical changes are more complex and include (but are not limited to) mineral phase decomposition, alkalization, and the formation of new crystalline and glass phases. Various gases circulating in the BF change the composition of the existing mineral phases and cause the formation of new phases acting as agents for the transport of components through pores. The synthetic equivalents of minerals that have so far been found in tuyere coke but are not observed in primary coke are gupeiite, Fe3Si; xifengite, Fe5Si3; schreibersite, Fe3P; barringerite, Fe2P; oldhamite (Ca, Mg, Fe, Mn)S; Al2O3 (corundum crystals); spinel, MgAl2O4; and fersilicite, FeSi. We describe here a case study of spinel crystals, which represents the first report on the occurrence and crystalline features of this mineral in tuyere coke. A number of coke samples were selected from drill core 130,303,203, obtained using a mobile tuyere rig from the tuyere zone of the BF at Rautaruukki Steel Works (Raahe, Finland). The samples were cut into pieces about 20-mm long, 20-mm wide, and 5-mm thick, preserving one origi-
STANISLAV GORNOSTAYEV, Research Scientist, and JOUKO HÄRKKI, Professor, are with the Laboratory of Process Metallurgy, University of Oulu, FIN-90014, Finland. Contact e-mail: [email protected] Manuscript submitted April 26, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS B
nal surface. The cut pieces were fixed to 28 48 1-mm glass plates and studied with a JEOL* JSM-6400 scanning *JEOL is a trademark of Japan Electron Optics Ltd., Tokyo.
electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS), which was also widely used for observing and identifying the minerals and other phases reported here. A number of small (3 to 15 m) crystals and aggregates of almost pure spinel, MgAl2O4 (EDS spectrum data), were found in two samples of the coke, selected from the 150and 210-cm levels (from the beginning of the tuyere) in the drill core. The spinels occur as euhedral, equidimensional crystals of dodecahedral and octahedral habit, as twins of octahedral and prism habit and as irregular crystals and their aggregates. Combination of forms should also be ment
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