A Study on the Viscous Behaviour with K2O Additions in the CaO-SiO2-Al2O3-MgO-K2O Quinary Slag System

The viscosities of CaO-SiO2-20wt%Al2O3-10 wt%MgO-K2O quinary slags with CaO/SiO2 from 0.8 to 1.2 at 1773K with 1-5 wt% K2O additions were measured to estimate the effect of K2O on the viscous behaviour of the slags. The measured viscosity at 1773 K increased with K2O addition at a fixed CaO/SiO2, which is contrary to the effect of Na2O on the viscosity of BF slags. To qualitatively verify the changes in slag structure, FT-IR spectroscopy was used. It was found that K2O induces Al2O3 to behave as an acidic oxide by forming [AlO4](5-)-tetrahedral units by the ionic compensation effect of K+ cations. However, regarding the effect of K2O on the silicate structure, it is observed that K2O has a negligible effect due to the consumption of O-2(-) with the formation of [AlO4](5-)-tetrahedral units. Furthermore, it is also found that Si-O-Al bending became more complicated with K2O additions, which supports the selective effect of K2O on the aluminate structure of the slag. In spite of the more complicated structure with K2O additions, the critical temperature (T-CR) decreased due to the gradual reduction of the liquidus temperature (T-LO) of the slags.