Investigation of the Viscosity and Structural Properties of CaO-SiO 2 -TiO 2 Slags
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TRODUCTION
TiO2-containing slags are significant in the processes of ironmaking, steelmaking, and Ti-recycling industries. In the continuous casting of steel, TiO2 is widely used as one of the most important component to replace CaF2 in mold fluxes, since fluorides will cause severe damage to equipment and pollute the environment.[1] Analogous to the role of CaF2, the addition of TiO2 exerts a deep influence on the viscosity of fluoridefree mold fluxes to provide lubrication between the steel and the mold.[2,3] Moreover, slags containing the CaOSiO2-TiO2 (CST) system are considered to have the heat-transfer function because the crystallization ability of crystals such as CaOÆSiO2ÆTiO2 or CaTiO3 is comparable to cuspidine (3CaOÆ2SiO2ÆCaF2) in commercial mold fluxes.[2,4,5] Therefore, slags containing the CST system are proposed as the most promising candidate for fluoride-free mold flux. Titanium resources are comparatively abundant in China, and most of them exist in the form of vanadium– titanium magnetite (VTM) ore. A complete set of blast furnace processes is adopted to extract metal from the VTM ore. In this process, most of iron and part of vanadium are reduced into the hot metal, while nearly KAI ZHENG, Master Degree Candidate, is with the Department of Energy and Resource Engineering, College of Engineering, Peking University, Beijing 100871, P.R. China. ZUOTAI ZHANG and XIDONG WANG, Professors, and LILI LIU, Doctor, are with the Department of Energy and Resource Engineering, College of Engineering, Peking University, and also with the Beijing Key Laboratory for Solid Waste Utilization and Management, Peking University. Contact e-mail: [email protected] Manuscript submitted October 28, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
all Ti components are left in the blast furnace slag. During the Ti recycling process, it is necessary to concentrate the entire Ti element in the slag into a certain Ti-containing phase such as anosovite and perovskite under chosen conditions.[6–8] As one of the most important physical properties of slag, the viscosity is closely related to the crystallization behavior of molten slag. Understanding the viscosity behaviors of slags with different contents of TiO2 is also essential in optimizing the operations for continuous-casting and blast-furnace processes.[9,10] It is well known that the macroscopic physical and chemical properties of slags are primarily determined by the microscopic structures. Consequently, to discover the mechanism of the influence of TiO2 addition on the viscosity of silicate slags, it is of crucial importance to analyze the structure of TiO2-bearing slags in detail, especially the role and coordination condition of Ti4+. Previous studies mainly concentrated on the slags with complex compositions and relatively small ranges of TiO2 content,[3,11–13] and the existence of some extra oxides such as Al2O3, B2O3, and MgO makes it difficult to execute a penetrating analysis into the structural role of Ti in slags. However, the research work on the property and structu
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