Influence of Al2O3 and SiO2 on the structure and viscosity of iron-compound bearing calcium-aluminosilicate slags

Abstract

The effect of the addition of Al 2 O 3 on the viscosity of the iron-compound bearing CaO-SiO 2 -Al 2 O 3 -MgO slags with different SiO 2 content (= 30, 40, and 50 wt%) was investigated at high temperatures. The addition of Al 2 O 3 increased the viscosity of iron-compound bearing calcium-aluminosilicate melts. The addition of Al 2 O 3 to the slag at low-SiO 2 content (= 30 wt%) increased the fraction of Fe 2+ at a fixed iron content because Fe 3+ cations prefer to exist as tetrahedral unit, i.e., Fe 3+ [IV], in the melt. On the other hand, the addition of Al 2 O 3 to the slag at high-SiO 2 content (= 50 wt%) increased the fraction of Fe 3+ at a fixed iron content due to the preference of octahedrally coordinated Fe 3+ [VI] in the slag. Although the redox equilibrium reaction of iron in the CaO-SiO 2 -Al 2 O 3 -Fe t O-MgO system was strongly affected by the basicity of the melt, the addition of Al 2 O 3 polymerized silicate networks regardless of the SiO 2 content in the slags. The activation energy for the viscous flow of the slags had a linear correlation with the non-bridged oxygen per tetrahedron (NBO/T) in the aluminosilicate network. Therefore, the viscosity of the iron-compound bearing calcium-aluminosilicate melt was determined by the degree of polymerization within the aluminosilicate networks. • Viscosity-structure relationship of iron-compound bearing calcium-aluminosilicate system was experimentally confirmed. • Al2O3 increased melt viscosity due to polymerization reaction and redox equilibria of iron-compound. • Activation energy of viscous flow was dominantly affected by degree of polymerization of slag.