Effect of SiO2 Content and Mass Ratio of CaO to Al2O3 on the Viscosity and Structure of CaO–Al2O3–B2O3–SiO2 Slags

• Published in: ISIJ International Vol. 63; no. 1; pp. 1 - 9
• Main Authors: Wen, Yongpeng, Shu, Qifeng, Lin, Yong, Fabritius, Timo
• Format: Journal Article
• Language: English
• Published: The Iron and Steel Institute of Japan 15.01.2023
• Subjects: mould fluxes; Raman spectroscopy; structure; viscosity; X-ray photoelectron spectroscopy
• ISSN: 0915-1559; 1347-5460
• DOI: 10.2355/isijinternational.ISIJINT-2022-288

The development of mold fluxes for continuous casting is one of major challenges to produce high aluminum steel. The CaO–Al2O3–B2O3 based mold flux is one of the potential candidates for casting high aluminum steel but its composition and properties still need to be optimized. In this work, the effect of silica and mass ratio of CaO to Al2O3 on the viscosity and structure of slag are studied. The viscosity of CaO–Al2O3–B2O3–SiO2 slag with varying SiO2 content (3%, 5%, and 7%) and mass ratio of CaO to Al2O3 (0.8, 1, and 1.2) were measured by rotating cylinder method at temperatures between 1723 K and 1873 K. It was found that the addition of SiO2 leads to the increase of the slag viscosity and the activation energy increases from 178.6 to 203.4 kJ/mol. In contrast, the increase of mass ratio of CaO to Al2O3 will reduce the viscosity of slag and the activation energy decreases from 227.1 to 191.0 kJ/mol. The structures of glassy CaO–Al2O3–B2O3–SiO2 slags were investigated by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Deconvolutions on Raman spectral reveal that silicon mainly exists as Q0(Si) and Q1(Si) in glasses. According to deconvolution results of XPS, as SiO2 content in glassy slag increases, the number of bridging oxygens increases, indicating a more polymerized structure. In contrast, the increase of the ratio of CaO to Al2O3 contributes to the depolymerization of glassy slag. The structural variations with different SiO2 contents and mass ratio of CaO to Al2O3 can be correlated to the viscosity variation of slag.