Microstructure detection of CaO-SiO2-based mold flux at high temperature by in-situ Raman spectroscopy

In this study, in-situ high-temperature Raman spectroscopy was used to analyze the Raman spectra of two groups of CaO-SiO 2 -based mold fluxes with a basicity of 1.35 from room temperature (25 °C) to 1300 °C. The differences between the Raman spectra obtained by this method and those obtained by the conventional method in studying the melt structure were compared. The Raman spectrum of solid slag at room temperature was the most obvious at 910 cm −1 , and there was a long-range ordered spectral peak at 350 cm −1 in the low-wavenumber region. As the temperature increased, the sharp characteristic peaks of the crystal structure gradually transformed into a relatively smooth envelope, and the spectral peaks in the low-wavenumber region disappeared after complete melting. In addition, compared with the Raman spectrum peak of the molten slag, the spectral peak of the glassy slag sample exhibited an obvious blue shift . For the N group, the changes in the degree of polymerization (DOP) of the two samples were consistent with the changes in viscosity , while for the F group, they were opposite. As the CaF 2 content increased from 14.92 wt% to 24.87 wt%, the DOP of the melt decreased from 0.38 to 0.31, which was consistent with the actual viscosity change trend. In contrast, the DOP of the glassy samples increased from 0.55 to 0.58. Therefore, when analyzing the structure of slag with a higher fluorine content, the high-temperature Raman spectroscopy method is more reliable. • An in-situ confocal micro-Raman spectrometer with a maximum detection temperature of 1500 ℃ was used in the experiment. • Raman spectral characteristics of high basicity CaO-SiO 2 based mold fluxes 25–1300 ℃ were tested and analyzed. • The advantages of using high temperature Raman method to study the structure of silicate melt were analyzed.