Effect of MgO on the Viscosity and Structure of CaO-Al2O3-B2O3-Based Non-reactive Mold Flux

The effect of MgO on the viscosity and structure of CaO-Al2O3-B2O3-based non-reactive mold flux was studied by rotational viscometer, molecular dynamics (MD) simulations, and Raman spectroscopy. The results show that with the increase of MgO content from 3 °C to 9 pct, the viscosity (the testing temperature is 1300 °C) of the sample decreases from 0.39 to 0.26 Pa seconds, the activation energy decreases from 158.7 to 119.7 kJ/mol, and the break temperature (Tbr) decreases from 1212 °C to 1157 °C. Triple-coordinated oxygen and highly coordinated Al appear in the mold flux to compensate for the excess negative charge of [AlO4]5- tetrahedron. With the increase of MgO content, the stability of the Al-O network structure is enhanced, but the degree of polymerization of melt and the complexity of network structure decrease. With the increase of MgO content, the amount of bridging oxygen in the system decreases, and the polymerization degree of the aluminate network in mold flux decreases. The results of Raman spectra are consistent with those of MD simulation. Therefore, MgO can simplify the melt structure and reduce the viscosity of mold flux.