In order to clarify the viscosity of FeO–SiO
2–V
2O
3–TiO
2–Cr
2O
3 system as the main components of vanadium slag with varied Cr
2O
3 and TiO
2 contents, the viscosity and structure characteristics of the slag were investigated by the rotating cylinder method and Raman spectroscopy, respectively. The results showed that the viscosity was decreased to 3.5 Pa·s at temperature above 1534 K for the FeO–SiO
2–V
2O
3 system, and the polymerization degree of this system was low due to the main structure of silicate as monomer. Meanwhile, V
3+ mainly existed in the form of V–O–V as a chain structure in FeO–SiO
2–V
2O
3 system, which slightly enhanced the polymerization degree of the slag. With the introduction of 6 mass% Cr
2O
3 into FeO–SiO
2–V
2O
3 system, the viscosity increased rapidly and was decreased to 3.5 Pa·s until temperature higher than 1767 K, and the polymerization degree of the slag was enhanced drastically due to the formation of Q
2 and Cr–O–Cr band in a chain structure as well as the formation of Q
3 species in a sheet structure. Furthermore, part of the chromium existed in the form of the high melting point of spinel (FeCr
2O
4). With the introduction of 13 mass% TiO
2 into the FeO–SiO
2–V
2O
3–Cr
2O
3 system, the viscosity decreased and was of 3.5 Pa·s at 1624 K, and the polymerization degree of the slag became weak due to the formation of discrete Si–O–Ti and Ti–O–Ti inhibiting the formation of sheet structure and hampering the crystallization of FeCr
2O
4 in molten slag, which was advantageous to decrease the viscosity of FeO–SiO
2–V
2O
3–Cr
2O
3–TiO
2 system.
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