An Insight in the Viscosity–Temperature Property of CaO‐SiO2‐Al2O3‐Based Slag Systems from Melt Structure

Viscosity is an important property for CaO‐SiO 2 ‐Al 2 O 3 ‐based slag systems, which showcases different scenarios in basic and acid slag systems with temperature change. This article elucidates the mechanism of their difference in viscosity–temperature property from melt structure. Results reveal that basic slag shows a low degree of polymerization (DOP) and a low viscosity of the melt due to an excessive O 2− ions depolymerizing the complex network structures, resulting in more low‐polymerized Q 0 (Si) units and less high‐polymerized Q 3 (Si) units. With the temperature decreases, the DOP and viscosity do not change significantly. However, the low DOP and viscosity favor crystal precipitation in the melt, leading to a solid–liquid mixed state of the slag, and thus a sharp increase in viscosity when the temperature decreases to 1275 °C. For acid slag, it undergoes a transformation into aluminosilicate structures with the introduction of numerous [AlO 4 ] 5− tetrahedra, accompanied by a significant increase in the relative mole fraction of high‐polymerized Q 3 (Si) units. Consequently, the DOP and viscosity are obviously higher than that of the basic slag. Furthermore, the DOP and viscosity of the acid slag increase continuously with the temperature decreasing, thus impeding crystal precipitation and enhancing the glass transition tendency of the molten slag.