Effect of alkaline earth metal oxides on the viscosity and structure of the CaO-Al2O3 based mold flux for casting high-al steels

The effect of BaO and MgO content on the viscosity and structure of the CaO-Al2O3 based mold flux system has been studied in this article. The viscosity results suggested that the addition of BaO tends to increase the viscosity of flux system, due to the polymerization of the melts network structure that leads to the increase of the apparent activation energy for viscous flow. However, the addition of MgO tends to decrease the viscosity of the slag melt, in which the free O2- ions depolymerize the network structure leading to the reduction of melt flow resistance and apparent activation energy. The results of FTIR (Fourier transform infrared) and Raman for the molten structures showed that the released O2- ions by BaO and MgO, working as network breaker, can break SiO bonds for the [SiO4]4 −-tetrahedral structure units; leading to the reduction of the symmetric Q1([Si2O7]6 −) stretching vibrations and the increase of symmetric Q0([SiO4]4 −) stretching vibrations. While for [AlO4]5 −-tetrahedral structure units, they would be connected and the aluminate-silicate network structure become more complicated due to the strong charge compensation effect that BaO introduced. However, the major role that MgO played is to release O2- ions to depolymerize the complex network structure, due to its weak charge compensation effect.