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 1773 K 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 Al ₂O3 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 [AlO ₄]^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_LQ) of the slags.