To have a further study for fluorine‐free mold fluxes, the structure, viscosity characteristics, and crystallization behavior of CaO–SiO2–B2O3‐based melts are studied combing molecular dynamics (MD) simulation and various experiments. The results show that, in the ternary CaO–SiO2–B2O3 glass system, stable structural units of [SiO4]4− tetrahedral, [BO3]3− trihedral, and [BO4]5− tetrahedral formed and the B2O3 addition polymerizes the Si–O network structure to some extent, whereas the influence on B–O network structure various with its content. In fluorine‐free mold fluxes, the viscosity at 1300 °C and melting temperature decrease with B2O3 addition, whereas the polymerization degree of slag network structure changes little, indicating that the melting property change plays a predominant role in decreasing the viscosity at 1300 °C. Moreover, due to the solid precipitation, the viscosity‐temperature curve of fluorine‐free slag in the range w(B2O3) = 4–6 wt% shows the characteristics of alkaline slag, whereas it shows the characteristics of acidic slag in the range w(B2O3) = 8–12 wt%. The MD simulation and experiment results are verified and complemented each other.
In this study, the structure, viscosity characteristics, and crystallization behavior of CaO-SiO2-B2O3 based melts were studied combining molecular dynamics (MD) simulation, Fourier transform infrared (FTIR) spectroscopy, rotating viscometer test, and FactSage thermodynamic calculation. The results showed that, in the ternary CaO-SiO2-B2O3 glass system, stable structural units of [SiO4]4− tetrahedral, [BO3]3− trihedral and [BO4]5− tetrahedral were formed, and the Si-O and B-O structure depolymerize with the basicity increase from 1.15 to 1.25, then the B-O structure become complex with the basicity further increase to 1.35. In fluorine-free mold fluxes, with the basicity increases, the viscosity at 1300 °C increases, the liquidus temperature decreases and then increases, the network structure polymerizes, it indicates that the structural complexity rather than the melting property change plays a predominant role in increasing the viscosity at 1300 °C. Moreover, due to the changes in crystallization phase and solid solution ratio, the viscosity-temperature curve of fluorine-free slag shows the characteristics of alkaline slag and the break temperature increase with the basicity increase. The MD simulation, FTIR experiment, viscosity test, and FactSage calculation results are verified and complemented each other.
The influence of BaO contents on structure and fluid behavior of fluorine-free CaO-SiO2-B2O3 based melts were examined using molecular dynamic (MD) simulation, rotary viscometer, X-ray diffraction and Fourier transform infrared spectroscopy. The FTIR results matched well with the MD simulation results that with the addition of BaO contents in CaO-SiO2-B2O3 based melts, more cations were provided to balance the negative charge of [BO4]5– tetrahedrons, leading to the structures of Si-O and B-O were more aggregated and the adjacent structural units were more closely connected, which made the structure complex, so the viscosity of mold fluxes at high temperature in the basicity range 1.15–1.25 was intensify. Meanwhile, when BaO replaced CaO under distinctive basic conditions, the viscous activity of fluorine-free mold flux was decreasing generally, showing that as the temperature was decreased, the tendency of slag to converge into complex network structural units was also decreasing, which states the improvement of lubrication capacity of the slag during cooling process.
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