Effects of Basicity on the Phase Composition, Structure, Viscosity, and Crystallization Temperature of CaO-SiO2-Al2O3-MgO-B2O3 Slags

The effect of basicity on the phase composition, structure, viscosity and crystallization temperature of CaO-SiO2-Al2O3-MgO-B2O3 fluorine-free slags was studied using vibrational viscometry and thermodynamic phase composition modeling in combination with Raman spectroscopy. The viscosity of the studied slags was established to depend mainly on the phase composition. Despite the complex reticular structure, consisting mainly of [SiO4] and [BO4] structural units with a large quantity of bridging oxygen, long slags (having a wide temperature range of viscosity variations) with low basicity possess high flowability in a liquid state as well as a low temperature of crystallization. This can be explained by the fact that the introduction of boron oxide is accompanied by the formation of a significant quantity of low-melting phases (CaO-B2O3, 2CaO-B2O3, and CaO-MgO-2SiO(2)) in the slag, which reduces the slag crystallization temperature, as well as increases its overheating and decreases viscosity. At an increase in basicity, long slags smoothly transform into short ones (with a narrow temperature range of viscosity variations); moreover, their structure is simplified along with an increase in the quantity of high-melting phases. In this case, despite the structural simplification, the slag crystallization temperature increases, which leads to the reduction in the degree of overheating and an increase in the viscosity.