Ilmenite smelting is a carbothermic reduction process to upgrade the mineral ilmenite (FeTiO
3) for subsequent TiO
2 pigment production, yielding a TiO
2-rich slag (generally, TiO
2 > 70 mass pct) as the main product and pig iron as the by-product. The ilmenite smelting process using an electric submerge arc furnace (SAF) technology has already become a dominant process for producing high-titania slag worldwide[
1] During the smelting process, an inevitable problem is the sudden surges of a foamy high-titania slag, sometimes becoming uncontrollable and thereby prolonging the melting time. It is generally believed that this foaming phenomenon is due mainly to the insufficient slag fluidity caused by changes in slag temperature or composition during the smelting process[
2] Furthermore, the fluidity of high-titania slag has a direct effect on the tapping behavior of the molten slag, the separation of the liquid slag and molten iron, and the SAF energy consumption.[
3] Hence, relatively suitable viscosity of high-titania slag is the guarantee for the smooth operation and optimization of the SAF smelting process.
A preliminary literature survey indicated that very few publications deal with investigation of the viscosity of high-titania slag (TiO
2 > 70 mass pct). We even could not find any publications concerning the viscosity of high-titania slags before 1963. In the early studies, Russian investigators[
4] studied some synthetic TiO
2-containing slag systems (18 to 92 mass pct TiO
2) and concluded that completely molten synthetic titania slags exhibit low viscosities in the order of 1 to 3 dPa s. However, more specific data were not released in their paper. Tuset[
5] reported the viscosity measurements of 54 different slags located in the TiO
2-Ti
2O
3-MgTiO
3 ternary system in 1968. He concluded that the completely molten slags are considerably fluid and have a low level of viscosity values, ranging from 0.5 to 1 dPa s. Furthermore, he also claimed that, above the liquidus temperature, viscosities of the studied slags are almost independent of slag composition and temperature. Unfortunately, Tuset did not show any of his results on the measured viscosity data in tables or graphs. From 1971 to 1978, Handfield and Charette[
2] published the viscosity of industrial high-titania slags (renowned as Sorel slag, which contains approximately 72 mass pct TiO
2). Grau and Poggi[
6] investigated viscosity variation of the QIT slag with temperature [QIT slag was a high-titania slag (TiO
2 > 72 mass pct) produced by Quebec Titanium Iron Company (QIT), Canada]. These researchers obtained a consistent conclusion that high-titania slag exhibited a very low level of viscosity values stabilized at around 0.3 dPa s. Besides, these values almost stayed constant with change in temperature and slag composition above the liquidus temperature. In 2009, Borowiec[
7] obtained almost identical conclusions for QMM slags (95 mass pct TiO
2); however, only a set of viscosity data was published in his paper. Until recent years, several researchers have begun to study the viscosity of high-titania slags again. In our previous work,[
3,
8] we measured viscosities of 24 different synthetic high TiO
2 slags (45 to 88 mass pct TiO
2) and reached some similar conclusions with the early studies mentioned above.[
2,
6,
7] However, our previous experimental viscosity values (around 0.65 dPa s) were slightly higher than those in the mentioned literature. Kim
et al.[
9] experimentally measured the viscosity of TiO
2-FeO binary slags and published three sets of similarly low level of viscosity data in their paper. Zhang
et al.[
10] first conducted a thermodynamic simulation and then experimentally studied the viscosity of the TiO
2-FeO-Ti
2O
3 ternary slags. They also found that once completely melted, high titania slags displayed very low viscosity and were very insensitive to the temperature and slag compositions.
It is well known that the high-temperature viscosity measurement of metallurgical slags is time consuming and costly work because the high-titania slags have characteristics of high melting points (above 1650 °C) and high reactivity as well as being corrosive toward all the ceramic containers. Thus, constructing an effective viscosity model to reproduce the viscosity of these slags is a important task. In the past decades, a wide variety of models has been proposed by researchers.[
11‐
20] However, most were developed to deal with molten silicate slags. When it comes to TiO
2-bearing slags (TiO
2 < 40 mass pct), only a few viscosity models[
21,
22] are applicable. The viscosity models for high-titania slags (TiO
2 > 70 mass pct) have not been reported in the literature to date because high-titania slags are noticeably structurally different from the traditional polymerizing silicate slags[
2] and their high-temperature structure is still unknown to metallurgists. Thus, it is crucial to find a model that describes the temperature and composition dependence of the viscosity of high-titania slag by using a few adjustable parameters.[
23]
In the present work, the viscosities of TiO
2-FeO and TiO
2-FeO-Ti
2O
3 slags were measured experimentally using the rotating cylinder method under argon atmosphere. The present measurements together with our previous measurements as well as the literature data[
8‐
10,
24] were used to optimize the present viscosity model. This model was developed according to the modification of the Vogel[
25]-Fulcher[
26]-Tammann[
27] (VFT) semi-empirical formalism. The new viscosity model can describe the viscosities of the TiO
2-FeO-Ti
2O
3 ternary high-titania slag system in broad composition and temperature ranges, including the solid-liquid slurries.