Investigation on Crystallization of CaO-Al2O3-B2O3-BaO Slag Using Differential Scanning Calorimeter and In Situ High-Temperature Raman Spectroscopy

CaO-Al2O3-B2O3-based slag is among the most promising "nonreactive" mold fluxes for continuous casting of high-aluminum steel. However, CaO-Al2O3-B2O3-based slag system exhibits a stronger crystallization ability compared to traditional mold fluxes. Herein, calcium oxide in CaO-Al2O3-10%B2O3 slag is partially replaced by the same mass of barium oxide (5 and 10 mass%) to adjust the crystallization ability. The crystallization of glassy slags is then investigated using a differential scanning calorimeter and their crystallization kinetics are analyzed using the Matusita-Sakka model. The structural evolution of glassy slags from room temperature to 1200 degrees C is also investigated using in situ Raman spectroscopy. The kinetic analysis shows that the crystallization process of CaO-Al2O3-B2O3-BaO glassy slags follows the surface crystallization mechanism. The predominant crystalline products are calcium monoaluminate (CaAl2O4) and calcium borate (Ca3(BO3)2). The partial replacement of calcium oxide by barium oxide inhibits the growth of CaAl2O4 in the slag by increasing the activation energy of crystal growth. The high-temperature Raman spectroscopy study shows that the band between 700 and 900 cm-1 gets weaker relative to the band between 450 and 650 cm-1 at high temperatures. This indicates the strengthening of bending vibration of Al-O-Al, which is consistent with the precipitation of CaAl2O4 with full oxygen bridging.