A comprehensive investigation on the viscosity and structure of CaO-SiO2-Al2O3-MgO-BaO slag with different Al2O3/SiO2 ratios

Abstract

In this study, the effect of Al2O3/SiO2 mass ratios on the viscosity and structure of a CaO-SiO2-MgO-Al2O3-BaO slag system was comprehensively investigated using multiple characterization methods. The results indicated that viscosity gradually decreased as the Al2O3/SiO2 ratio increased from 0.34 to 0.69. FTIR analysis revealed that the Si-based and Al-based structures and Si-O-Al bonds were weakened. Raman spectroscopy further suggested that the complexity of the Si-based structure was reduced because of the transformation from polymerized Q3 and Q2 units to simpler Q0 and Q1 units. The changes in the numbers of bridged oxygen (O0), non-bridged oxygen (O-), and free oxygen (O2–) atoms with increasing Al2O3/SiO2 ratio were quantified through XPS; the results revealed that the content of O0 decreased, whereas the O- and O2– contents showed the opposite trend. 27Al MAS NMR spectroscopy indicated that the relative content of the [AlO5] and [AlO6] network modifiers increased and that of [AlO4] decreased with increasing Al2O3/SiO2 ratio. This confirmed that the substitution of SiO2 with Al2O3 depolymerized the complicated network structure to some extent, leading to a reduction in the slag viscosity.