Insight into the Relationship Between Viscosity and Structure of CaO-SiO2-MgO-Al2O3 Molten Slags

This article elucidates the quantitative relationship between viscosity and structure in a basic slag system of CaO-SiO2-MgO-Al2O3 and focuses on the role of Al2O3. Slag viscosity was measured by the rotating cylinder method, and structural information was obtained using Fourier transformation infrared, Raman and magic angular spinning nuclear magnetic resonance (MAS-NMR) techniques. The results show that, as the Al2O3 content increased, slag viscosity increased initially and decreased afterwards, directly indicating that Al2O3 had an amphoteric effect on slag viscosity. The Raman spectra verified that with increasing Al2O3 content, the concentrations of Q0(Si) and Q2(Si) decreased first and then increased, while that of Q1(Si) kept increasing and that of Q3(Si) increased first and then decreased. The 27Al MAS-NMR spectra proved that the mole ratios of AlO5 and AlO6 to AlO4 kept increasing with the increase of Al2O3 content, and, overall, Al2O3 changed from a network former to a network modifier. The relationship between the viscosity and structure of the molten slags was further analyzed quantitatively based on the modified (NBO/T), denoted as (NBO/T)′, and we found a fine linear correlation between the logarithm of viscosity and (NBO/T)′. Moreover, the variations of thermodynamic properties of this system also indirectly supported the present experimental results.