Effect of Cooling Rate on the Structure of CaO–SiO₂–CaF₂-based Glassy Mold Flux

Abstract

To evaluate the effect of cooling rate on the structure of CaO–SiO₂–CaF₂ based mold flux, the structure of glassy mold fluxes prepared at different cooling rates ranging from 20°C/s to 100°C/s were investigated by Raman spectroscopy, ²⁹Si MAS-NMR and XPS techniques. The results shown that the structural species Q² and Q³ slightly increased with the increase of cooling rate, while the ratio of Q⁰ slightly decreased. The change of Q¹ was negligible. The average number of bridging oxygen atoms increased with the increase of cooling rate. The polymerization degree of the silicate structural network of glassy CaO–SiO₂–CaF₂-based mold fluxes was found to increase with the increase of cooling rate. The change of the cooling rate obviously caused the structural change of the CaO–SiO₂–CaF₂ mold flux. The faster the cooling rate, the higher temperature structural feature was founded. The effect of the cooling rate on F-bonds was negligible, and F was found to be mainly in the form of F–Ca bonds.