University of Oulu

Wen, Y., Shu, Q., Lin, Y., & Fabritius, T. (2023). Effect of SiO₂ Content and Mass Ratio of CaO to SiO₂ on the Viscosity and Structure of CaO–Al₂O₃–B₂O₃–SiO₂ Slags. ISIJ International, 63(1), 1–9.

Effect of SiO₂ content and mass ratio of CaO to Al₂O₃ on the viscosity and structure of CaO–Al₂O₃–B₂O₃–SiO₂ slags

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Author: Wen, Yongpeng1; Shu, Qifeng2; Lin, Yong3;
Organizations: 1School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing, China
2Process Metallurgy Research Unit, University of Oulu, Oulu, Finland
3Ganjiang Innovation Academy, Chinese Academy of Sciences, Ganzhou, China
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.6 MB)
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Language: English
Published: Iron and Steel Institute of Japan, 2023
Publish Date: 2023-08-09


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.

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Series: ISIJ international
ISSN: 0915-1559
ISSN-E: 1347-5460
ISSN-L: 0915-1559
Volume: 63
Issue: 1
Pages: 1 - 9
DOI: 10.2355/isijinternational.ISIJINT-2022-288
Type of Publication: A1 Journal article – refereed
Field of Science: 216 Materials engineering
Funding: Financial supports from national science foundation of China (contract no. 51774026) and Business Finland for Towards Carbon Neutral Metals project (TOCANEM) are sincerely acknowledged.
Copyright information: © 2023 The Iron and Steel Institute of Japan. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs license (