Viscosity and structure evolution of CaO–SiO2–MgO–Al2O3–BaO slag with the CaO/SiO2 mass ratio of 0.9

Abstract Keeping a low and steady viscosity of slag is conducive to smooth operation of blast furnace. In this work, the effect of BaO on the viscosity and structure evolution of CaO–SiO2–MgO–Al2O3–BaO slag with a fixed CaO/SiO2 mass ratio of 0.9 was studied. The results revealed that the viscosity decreased firstly with BaO content rising from 0 wt% to 1.0 wt%, and then increased with further improving BaO content, which was ascribe to the contradictory effect of Ba2+ and O2− on the aluminate–silicate network structure. The structural analysis by Fourier transform infrared spectroscopy (FTIR) and Raman spectra showed that a small amount addition of BaO could promote the transformation from Q2 and Q3 units toward Q0 and Q1 units. However, the higher BaO content would induce an increasing concentration of Q2 and Q3 units, leading to an enhancement of the polymerization degree of slag. In addition, the variations of Al-related structural units were identified by the 27Al magic angle spinning nuclear magnetic resonance (27Al MAS-NMR) spectra. The relative fraction of [AlO4] units firstly decreased and then increased with the addition of BaO, and an opposite trend was observed for [AlO5] and [AlO6] units. The structural analysis supported the results of viscosity experiment well.