Effect of MgO and K₂O on high-al silicon– manganese alloy slag viscosity and structure

The viscosity, melting proprieties, and molten structure of the high-Al silicon–manganese slag of SiO₂–CaO–25 mass% Al₂O₃–MgO–MnO–K₂O system with a varying MgO and K₂O content were studied. The results show that with the increase in MgO content from 4 to 10 mass%, the measured viscosity and flow activation energy decreases, but K₂O has an effect on increasing those of slags. However, the melting temperature increases due to the formation of high-melting-point phase spinel. Meanwhile, Fourier transform infrared (FTIR) and X-ray photoelectron spectra (XPS) were conducted to understand the variation of slag structure. The O²⁻ dissociates from MgO can interact with the O⁰ within Si–O or Al–O network structures, corresponding to the decrease in the trough depth of [SiO₄] tetrahedral and [AlO₄] tetrahedral. However, when K₂O is added into the molten slag, the K⁺ can accelerate the formation of [AlO₄] tetrahedra, resulting in the increase in O⁰ and O⁻ and the polymerization of the structure.