Coupling effect of TiO₂ and Al₂O₃ on the structure of CaO-SiO₂-MgO-xwt%Al₂O₃-ywt%TiO₂ slag systems

Abstract

This study analyzes the influence of TiO₂ and Al₂O₃ contents on the microstructure of CaO-SiO₂-MgO-xwt%Al₂O₃-ywt%TiO₂ (14 ≤ x ≤ 22, 0 ≤ y ≤ 10) blast furnace slag systems based on the change of slag viscosity, Raman spectroscopy, and molecular dynamics. The Raman spectroscopy results indicate that an increase in TiO₂ content leads to the gradual depolymerization of complex silicate structures (Q_Si³ and Q_Si²) into simpler structures (Q_Si⁰ and Q_Si¹) in the slag. At the same time, the Al-O-Al bonds in the aluminate structures of the slag also depolymerize into simpler Al-O⁻ forms, resulting in a decrease in the degree of polymerization of both silicates and aluminates. In contrast, an increase in Al₂O₃ content generally results in an increased degree of polymerization for the silicates and aluminates. Molecular dynamics simulations of the polymerization and depolymerization processes in the microstructure of the blast furnace slag reveal that Si and Al mainly exist in tetrahedral [SiO₄]⁴⁻ and [AlO₄]⁴⁻, while Ti mainly exists in the form of simple pentacoordinate [TiO₅]⁶⁻ and hexacoordinate [TiO₆]⁸⁻. TiO₂ exhibits basic properties in this system, whereas Al₂O₃ demonstrates acidic behavior. The addition of TiO₂ introduces free oxide ions into the system, causing the bridging oxygens to break into non-bridging oxygens, leading to the depolymerization of complex structures Q_Si⁴ and Q_Si³, which simplifies the slag structure. On the other hand, an increase in Al₂O₃ content tends to capture or share the oxide ions within the system to form [AlO₄]⁴⁻, resulting in the polymerization of free oxygens into non-bridging oxygens, which further polymerize into bridging oxygens and lead to the consolidation of simple structures Q_Si⁰ and Q_Si¹, resulting in a more complex slag structure. Both Raman spectroscopy analysis and molecular dynamics simulation results indicate that the degree of polymerization of [SiO₄]⁴⁻ and [AlO₄]⁴⁻ in the slag network structure is a crucial factor determining the fluidity of the slag.

Keywords

aluminum oxide / titanium dioxide / blast furnace slag / structure / polymerization degree

References

[1] Xu RZ, Wang Z. Influence of Al₂O₃ on viscous behavior and structure characteristic of TiO₂-bearing molten slags. Ceram. Int., 2024, 50(13): 24016.

[2] Fan HL, Wang RX, Xu ZF, Duan HM, Chen DF. The effect of B₂O₃ on the structure and properties of titanium slag melt by molecular dynamics simulations. J. Mater. Res. Technol., 2021, 15: 1046.

[3] Deng ZY, Zhang XM, Hao GG, Wei CX, Zhu MY. Dissolution behavior of Al₂O₃ inclusions into CaO-MgO-SiO_2-Al₂O₃-TiO₂ system ladle slags. Int. J. Miner. Metall. Mater., 2024, 31(5): 977.

[4] Stebbins JF, Kroeker S, Keun Lee S, Kiczenski TJ. Quantification of five- and six-coordinated aluminum ions in aluminosilicate and fluoride-containing glasses by high-field, high-resolution ²⁷Al NMR. J. Non Cryst. Solids, 2000, 275(1–2): 1

[5] Yan ZM, Pang ZD, Lv XW, Qiu GB, Bai CG. Hysicochemical properties of high alumina blast furnace slag. The 9th International Symposium on High-Temperature Metallurgical Processing, 2018279.

[6] Zhang SF, Zhang X, Liu W, Lv XW, Bai CG, Wang L. Relationship between structure and viscosity of CaO-SiO₂-Al₂O₃-MgO-TiO₂ slag. J. Non Cryst. Solids, 2014, 402: 214.

[7] Gan L, Lai CB. A general viscosity model for molten blast furnace slag. Metall. Mater. Trans. B, 2014, 45(3): 875.

[8] Ohno A, Ross HU. Optimum slag composition for the blast-furnace smelting of titaniferous ores. Can. Metall. Q., 1963, 2(3): 259.

[9] Park H, Park JY, Kim GH, Sohn I. Effect of TiO₂ on the viscosity and slag structure in blast furnace type slags. Steel Res. Int., 2012, 83(2): 150.

[10] Sohn I, Wang WL, Matsuura H, Tsukihashi F, Min DJ. Influence of TiO₂ on the viscous behavior of calcium silicate melts containing 17 wt% Al₂O₃ and 10 wt% MgO. ISIJ Int., 2012, 52(1): 158.

[11] Yan ZM, Lv XW, He WC, Jian X. Effect of TiO₂ on the liquid zone and apparent viscosity of SiO₂-CaO-8wt%MgO-14wt%Al₂O₃ system. ISIJ Int., 2017, 57(1): 31.

[12] Handfield G, Charette GG. Viscosity and structure of industrial high TiO₂ slags. Can. Metall. Q., 1971, 10(3): 235.

[13] Kato M, Minowa S. Relation between the viscosity and electrical conductivity of molten slag. ISIJ Int., 1969, 55(4): 260

[14] Pang ZD, Lv XW, Jiang YY, Ling JW, Yan ZM. Blast furnace ironmaking process with super-high TiO₂ in the slag: Viscosity and melting properties of the slag. Metall. Mater. Trans. B, 2020, 51(2): 722.

[15] Matsui M. Molecular dynamics study of the structures and bulk moduli of crystals in the system CaO-MgO-Al₂O₃-SiO₂. Phys. Chem. Miner., 1996, 23(6): 345.

[16] H.E. Xie, W.Z. Yu, Z.X. You, X.W. Lv, and C.G. Bai, The effect of titanium carbonitride on the viscosity of high-titanium-type blast furnace slag, Metals, 9(2019), No. 4, art. No. 395.

[17] Zhen YL, Zhang GH, Chou KC. Viscosity of CaO-MgO-Al₂O₃-SiO₂-TiO₂ melts containing TiC particles. Metall. Mater. Trans. B, 2015, 46(1): 155.

[18] Kim GH, Sohn I. Effect of Al₂O₃ on the viscosity and structure of calcium silicate-based melts containing Na₂O and CaF₂. J. Non Cryst. Solids, 2012, 358(12–13): 1530.

[19] Xu CY, Wang C, Xu RZ, Zhang JL, Jiao KX. Effect of Al₂O₃ on the viscosity of CaO-SiO₂-Al₂O₃-MgO-Cr₂O₃ slags. Int. J. Miner. Metall. Mater., 2021, 28(5): 797.

[20] Chen BX, Hou J, You Y. et al.. Effects of Al₂O₃ content on the properties of BF slag and suitable fluxing regime for BF ironmaking with high Al₂O₃ content. Can. Metall. Q., 2023, 62(3): 617.

[21] Yan Z, Lv X, Zhang J, Qin Y, Bai C. Influence of MgO, Al₂O₃ and CaO/SiO₂ on the viscosity of blast furnace type slag with high Al₂O₃ and 5 wt% TiO₂. Can. Metall. Q., 2016, 55(2): 186.

[22] Mysen BO, Virgo D, Kushiro I. The structural role of aluminum in silicate melts—A Raman spectroscopic study at 1 atmosphere. Am. Mineral., 1981, 66: 678

[23] Mysen BO, Virgo D, Scarfe C. Relations between the anion structure and viscosity of silicate melts—A Raman spectroscopic study. Am. Mineral., 1980, 65: 690

[24] Mysen BO, Virgo D. Trace element partitioning and melt structure: An experimental study at 1 atm pressure. Geochim. Cosmochim. Acta, 1980, 44(12): 1917.

[25] Mysen BO, Finger LW, Virgo D, Seifert FA. Curve-fitting of Raman spectra of silicate glasses. Am. Mineral., 1982, 67(7–8): 686

[26] Mysen BO. Olivine/melt transition metal partitioning, melt composition, and melt structure-Influence of Al³⁺ for Si⁴⁺ substitution in the tetrahedral network of silicate melts. Geochim. Cosmochim. Ac., 2007, 71(22): 5500.

[27] Mysen BO, Virgo D, Scarfe CM, Cronin DJ. Viscosity and structure of iron- and aluminum-bearing calcium silicate melts at 1 atm. Am. Mineral., 1985, 70: 487

[28] McMillan P, Piriou B, Navrotsky A. A Raman spectroscopic study of glasses along the joins silica-calcium aluminate, silica-sodium aluminate, and silica-potassium aluminate. Geochim. Cosmochim. Acta, 1982, 46(11): 2021.

[29] McMillan P, Piriou B. Raman spectroscopy of calcium aluminate glasses and crystals. J. Non Cryst. Solids, 1983, 55(2): 221.

[30] Poe BT, McMillan PF, Coté B, Massiot D, Coutures JP. Structure and dynamics in calcium aluminate liquids: High-temperature ²⁷Al NMR and Raman spectroscopy. J. Am. Ceram. Soc., 1994, 77(7): 1832.

[31] Sun YQ, Wang H, Zhang ZT. Understanding the relationship between structure and thermophysical properties of CaO-SiO₂-MgO-Al₂O₃ molten slags. Metall. Mater. Trans. B, 2018, 49: 677.

[32] Wu T, He SP, Liang YJ, Wang Q. Molecular dynamics simulation of the structure and properties for the CaO-SiO₂ and CaO-Al₂O₃ systems. J. Non Cryst. Solids, 2015, 411: 145.

[33] S. Zhang, Y. Hou, J. Guo, H.H. Zhou, and X.W. Lv, Flowability and structural evolution of CaO-SiO₂-MgO-Al₂O₃ slag with varying MgO/CaO ratios: Experiments and MD simulations, J. Non Cryst. Solids, 634(2024), art. No. 122979.

[34] Mott NF. The viscosity of vitreous silicon dioxide. Phllos. Mag. B, 1987, 56(2): 257.

[35] Hou Y, Zhang S, Dang J, Guo J, Zhou HH, Lü XW. Viscosity and structure relationship with equimolar substitution of CaO with MgO in the CaO-MgO-Al₂O₃-SiO₂ slag melts. Int. J. Miner. Metall. Mater., 2025, 32(1): 70.

[36] Zhao YF, Li ZY, Li SJ, Song WL, Jiao SQ. A review of in situ high-temperature characterizations for understanding the processes in metallurgical engineering. Int. J. Miner. Metall. Mater., 2024, 31(11): 2327.

[37] Welch RS, Lee KH, Wilkinson CJ, Ono M, Bragatto CB, Mauro JC. Topological hardening through oxygen triclusters in calcium aluminosilicate glasses. J. Am. Ceram. Soc., 2021, 104(12): 6183.

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