Thermodynamics of TiO x in blast furnace-type slags
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EXPANDING the campaign life of the blast furnace is of a great concern in the steelmaking industry,[1,2,3] and premature hearth erosion is one of the most important factors limiting campaign life. There are several measures to reduce the erosion of the blast furnace hearth including the addition of the titania bearing materials into the charge of the blast furnace.[2–7] This is believed to promote the formation of a protection layer, so-called ‘‘titanium-bear,’’ on the refractory brick. The existence of the titanium-bear was confirmed in the dissection studies of blown-out furnaces, indicating that the deposited materials contained titanium carbonitride, a solid solution of titanium carbide, and titanium nitride.[1,8,9] Several investigations have been performed to measure the change in the slag properties, such as the liquidus temperature[7,10–12] and the viscosity,[7,13–15] caused by the usage of the titania bearing materials in blast furnaces. Fine and Arac[12] found that titanium oxide increases the liquidus temperature of CaO-SiO2-MgO-Al2O3 melts at low oxygen potential, 10215 atm, while the opposite results were derived by others at higher oxygen potential.[7,10,11] They suggested this effect was caused by suboxides of titanium, such as TiO1.5 or TiO. Handfield and Charette[14] studied the viscosity of slags containing TiO2 and pointed out that although a small addition of titanium oxide to blast furnaces will decrease the slag viscosity, larger additions could result in the increase of the bulk viscosity due to the solid partiY. MORIZANE, formerly Graduate Student, Department of Materials Science and Engineering, Carnegie Mellon University, is with Nippon Steel Corporation, Kitakyushu-city 804 Japan. B. OZTURK, Ph.D., formerly Research Faculty Member, Department of Materials Science and Engineering, Carnegie Mellon University, is with Johnson Matthey Company, Cranberry Township, PA 16066. R.J. FRUEHAN, Professor, is with the Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15213. Manuscript submitted May 28, 1997. METALLURGICAL AND MATERIALS TRANSACTIONS B
cles of carbonitride in the molten slags. Ohno and Ross[15] measured the slag viscosity under reducing conditions. Using CaO-SiO2-Al2O3-TiO2 slags contained in a graphite crucible under a carbon monoxide atmosphere, they found that the slag viscosity increases rapidly as the initial TiO2 content increases. These changes in the slag properties are not favorable for a blast furnace operation, since gas and liquid permeabilities inside the blast furnace are important aspects in the furnace operation, and since any difficulties in tapping the molten metal and slag out of the furnace could cause serious operational problems. Thus, the addition of titania bearing materials should be optimized to form a protection layer on the refractories without causing possible operational problems. The number of previous investigations dealing with the equilibrium between iron-carbon alloys and the blast furnace–type slags con
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