Investigation on the structure and viscosity of BaO-bearing slag melt through molecular dynamics simulation, Raman and 27Al MAS NMR spectra

Abstract

• BaO addition made the coordination numbers (CNs) of Al-O decreased. • The polymerization degree of slag increased based on the compensation effect. • The competitive action of Ba 2+ and O 2– determined the structure and viscosity. Studying the structure and viscosity of BaO-bearing slag was helpful for explaining the micro mechanism of its physicochemical property variations, and further guiding the utilization of bearing-barium ores for hot metal production. The structure of CaO-SiO 2 -10 wt% MgO-12 wt% Al 2 O 3 -BaO slag with BaO content varying from 0 to 5 wt% was studied based on the combined computational-experimental method, including the molecular dynamic (MD) simulation and experimental measurements of Raman spectroscopy and 27 Al magic angles pinning nuclear magnetic resonance ( 27 Al MAS-NMR) spectroscopy. The viscosity of the slag was measured, and the relationship between the viscosity and polymerization degree of the slag was established. MD simulation results indicated that the coordination numbers (CNs) of Si-O kept unchanged. The concentrations of four-coordinated Al units and bridged oxygen increased with an increase in BaO. The distribution of Q i units of Si and Al indicated that the structural units tended to be more complicated with the increasing BaO content. The result from Raman spectroscopy indicated that the amount of Q 2 and Q 3 units increased with the addition of BaO, while that of Q 0 and Q 1 units decreased. The results from 27 Al MAS-NMR spectroscopy showed that the relative concentration of [AlO 4 ] structural units increased from about 48 to 53 wt%, and an opposite trend was observed in [AlO 5 ] and [AlO 6 ] units, indicating that higher BaO content enhanced the polymerization degree of the slag. In addition, the viscosity of the slag increased with the rising BaO content, which was caused by the dominant effect of Ba 2+ .