Molecular Dynamics Simulation of the Structure and Properties of CaO-SiO 2 -CaF 2 Slag Systems
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IT is widely accepted that the microstructures of slag determine their macroproperties, especially their viscosity. CaF2 is a common flux used to adjust the viscosity, melting temperature, and crystallization rates of a slag. In the last decades, numerous studies[1–3] have used X-ray diffraction, Fourier transform infrared spectrometry (FT-IR), Raman Spectrometry, and nuclear magnetic resonance (NMR) to investigate the microstructures of molten slags and their effect on the macroproperties. Sasakiet et al.[2] studied the Na2O-NaF-SiO2 slag system and found that the polymerization of molten slag increases with substitution of O with F atoms. Fcombines with Si4+ to form nonbridging oxygen, and NaF acts as a diluent when Na2O/SiO2 £ 1.0. Another study by Mills et al.[4] indicated that CaF2 can break the complex anion structure of acidic silicate melts, which does not have a corresponding function in alkaline
SHENGPING HE, SAI WANG, BORAN JIA, MIN LI, and QIAN WANG are with the College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China. Contact e-mail: [email protected] QIANGQIANG WANG is with the College of Materials Science and Engineering, and Chongqing Key Laboratory of Vanadium-Titanium Metallurgy and Advanced Materials, Chongqing University, Chongqing 400044, China Manuscript submitted September 1, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
silicate melts but only acts as a diluent. NMR studies on the coordination of F in CaO-SiO2-CaF2-Na2O systems, as reported by Hayashi et al.,[5] showed that the number of coordinations between F and Ca ions increases from 0.23 to 0.3 at a ratio of nNa/(nNa + nCa). Tsunawaki et al.[6] investigated the effect of CaF2 on the microstructure of CaO-SiO2-CaF2 systems by using Raman spectroscopy, and they showed that CaF2 contributes to the breakage of some Si-O bonds for CaF2 amounts less than 20 mol pct for a basicity of less than 1. However, Luth et al.[7] found that the substitution of O with F ions increases the degree of polymerization (DOP), forming Ca-F complexes in the CaO-SiO2-CaF2 system. In contrast, Park et al.,[8] performed investigations on the effect of x(CaF2)/x(SiO2), x(CaO)/x(SiO2), and x(CaO)/ x(CaF2) on the structure of CaO-SiO2-CaF2 using FT-IR spectrometry, and they suggested that the silicate network depolymerizes with an increase in x(CaF2)/ x(SiO2), x(CaO)/x(SiO2), and x(CaO)/x(CaF2). Therefore, previous approaches have given contradictory results, and the mechanism of F on the microstructure of silicate melts remains unclear. Most metallurgical processes require high-temperature environments, making the measurement of molten slag microstructures a challenging task. An alternative method is quenching, which preserves the microstructure of the molten slag at high temperatures. However, it is incapable of providing all structural information. Recently, molecular dynamics (MD) simulations have been widely used to investigate the structure of silicate
melts, and previous reports[9–11] have shown good agreement with ex
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