Effect of CaF2 and CaO/Al2O3 on viscosity and structure of TiO2-bearing slag for electroslag remelting

• Published in: Journal of iron and steel research, international international, 2021-12, Vol.28 (12), p.1541-1550
• Main Authors: Ju, Jian-tao, Yang, Kang-shuai, Zhu, Zhi-hong, Gu, Yue, Chang, Li-zhong
• Format: Article
• Language: English
• Subjects: Applied and Technical Physics; Engineering; Machines; Manufacturing; Materials Engineering; Materials Science; Metallic Materials; Original Paper; Physical Chemistry; Processes
• ISSN: 1006-706X; 2210-3988
• DOI: 10.1007/s42243-021-00683-2

The relationship between the viscosity and structure of CaF 2 –CaO–Al 2 O 3 –MgO–TiO 2 slag with different CaF 2 contents and CaO/Al 2 O 3 ratios was studied using the rotating cylinder method, Fourier transform infrared spectroscopy, and Raman spectrometry. The activity coefficients of CaF 2 and the CaO/Al 2 O 3 ratio were determined to understand the correlation between viscosity and structure of the slag. The results suggest that the slag viscosity reduces gradually with an increase in CaF 2 content from 14.1 to 28.1 wt.% or CaO/Al 2 O 3 ratio from 0.9 to 1.5, and correspondingly apparent activation energy for viscous flow reductions. The addition of CaF 2 does not change the structure of the molten slag; however, the relaxation effect of the anionic species and the hindrance effect of the cationic species are promoted by substituting part of the non-bridging oxygens (NBO) with F − ions from CaF 2 , which is attributed to the formation of NBO–Ca 2+ –F − and NBO–Ca 2+ –NBO, respectively. However, as the CaO/Al 2 O 3 ratio increases, some of the Q 4 units in the aluminate structure are depolymerized into Q 2 units, so that the relative strength of the Al–O–Al linkage decreases, and the relative fraction of Ti 2 O 6 4− chains increases, whereas that of O–Ti–O chains decreases slightly, resulting in depolymerization on the slag structure. Additionally, the effect of the CaO/Al 2 O 3 ratio on the structure was greater than that of CaF 2 because of the greater depolymerization effect. The variation in the activity can indirectly explain the relationship between the viscosity and structure of the aluminate structural units based on thermodynamic analysis.