Different Roles of Iron Species in the Network Structure and Viscosity of Silicate Melts

Abstract

In iron-containing silicate melts such as gasification slags and geological slags, iron can play a different role in the melt properties because of its varying valence states. In this paper, the structural characteristics and viscosities of five samples were studied by molecular dynamics simulation and thermodynamic calculation methods. The effect of different iron species on the structure and properties is revealed. More than half of the Fe 3+ ions are in four-coordination. The four-and fivefold coordinated ferric ions are in dynamic equilibrium. The four-coordinated Fe 3+ can connect with the other tetrahedrons centered by Si 4+ and Al 3+ or integrate into three-coordinated oxygen units. With an increase of the iron content, the polymerization degree characterized by nonbridged oxygen per tetrahedra (NBO/T) is found to be inconsistent with the trend of viscosity. Based on the energy of the different types of oxygen, a new parameter RS total is proposed to substitute the original NBO/T and correlate with viscosity in an exponential function. Liquid iron can form in molten slags under a strong reducing atmosphere, which can inhibit the diffusion of oxygen and increase the viscosity.