Influence of Na2O on the thermodynamics properties, viscosity, and structure of CaO–SiO2–MgO–Al2O3–BaO–Na2O slag

Abstract

This article investigated the effect of Na2O on the viscosity and structure of CaO–SiO2–MgO–Al2O3–BaO–Na2O slag. To understand the stability of slag at high temperatures, the “excessive heat of slag” was calculated. The structure of slag was analyzed using Raman and 27Al magic angular spinning nuclear magnetic resonance (MAS-NMR) techniques. The results showed that the viscosity decreased with an increase in Na2O content in the range of 0 to 4 wt%, while the excessive heat of slag increased because the effect of slag composition on its heat capacity was more significant than that of temperature. From the perspective of heat supply, it should increase the fuel ratio of the blast furnace to ensure a stable furnace temperature when raising Na2O content. The mole fraction of Q Si0 (QSin, n is the number of bridging oxygen in a [SiO4]-tetrahedron) and Q Si2 increased gradually, whereas that of Q Si3 decreased obviously. The [SiO4]-tetrahedral structures were depolymerized, which reduced the number of bridging oxygen. Simultaneously, the increment in non-bridging oxygen caused the transformation from AlO4 to AlO5 and AlO6, thus decreasing the fraction of the network former (AlO4). The connection between [SiO4] and AlO5 or AlO6 weakened the strength of the network structure and increased the proportion of the Al–O bond.