Study on the Influence of TiO2 on the Viscosity and Fluidity of Ash Slag of Highly Acidic Coke at High Temperature

Abstract

The mobility characteristics of molten ash within coke matrices during blast furnace operations substantially influence coke quality parameters, rendering comprehensive investigation of this phenomenon critical for process optimisation in ferrous metallurgy. Although prior studies have demonstrated that TiO₂ reduces polymerization in basic slags, its role in governing the structural evolution of highly acidic, coke-derived molten ash remains poorly understood. Since coke ash typically exhibits characteristics of highly acidic slag systems, this study focuses on the SiO₂-Al₂O₃-CaO-TiO₂ quaternary system. Through integrated molecular dynamics simulations and experimental investigations, we systematically examine TiO₂’s influence on the structural evolution of molten ash and quantitatively assess its effects on viscosity and flow behaviour. The findings reveal that [SiO₄] and [AlO₄] tetrahedra constitute the fundamental structural units within molten ash. As TiO₂ content decreases, the population of [TiO_m] polyhedral structures diminishes, leading to a progressive simplification of the interconnected network. This structural modification correlates with reduced slag viscosity and enhanced fluidity. Furthermore, synergistic diffusion between Ti and Si atoms in the slag matrix demonstrates pronounced sensitivity to TiO₂ concentration. At 2 wt.% TiO₂, Ti exhibits greater diffusivity than Si. Viscosity reduction with decreasing TiO₂ content coincides with a decline in bridging oxygen species and an increase in non-bridging oxygen populations, indicative of molecular depolymerisation from large clusters to smaller fragments—a phenomenon corroborated by FTIR spectral analysis. These structural alterations suggest that elevated TiO₂ content enhances slag viscosity while concurrently improving coke mechanical strength through modified ash-phase interactions. We address this gap by revealing that TiO₂ modifies network connectivity differently in acidic environments, reducing polymerization by forming [TiO_m] polyhedra that disrupt Si-O-Al linkages. These findings highlight the compositional dependency of TiO₂’s structural effects, providing novel insights into optimizing coke performance in blast furnaces.