Crystallization of Slag Films of CaO-Al₂O₃-BaO-CaF₂-Li₂O-Based Mold Fluxes for High-Aluminum Steels' Continuous...

In this study, solidified films of CaO-Al₂O₃-BaO-CaF₂-Li₂O-based mold fluxes with different contents of Al₂O₃ addition were acquired by immersing an improved water-cooled copper probe in bulk molten slags. This probe can obtain films with representative structures. Different slag temperatures and probe immersion times were employed to investigate the crystallization process. The crystals in the solidified films were identified using X-ray diffraction, the morphologies of the crystals were observed using optical microscopy and scanning electron microscopy, and the kinetic conditions, especially the activation energy of devitrified crystallization in glassy slags, were calculated and discussed based on the differential scanning calorimetry. The results indicated that after adding extra Al₂O₃, the growing speed and thickness of the solidified films increased, and more time was required for the film thickness to reach a steady state. In addition, fine spinel (MgAl₂O₄) precipitated in the films at the early stage of solidification after adding 10 wt% of extra Al₂O₃. Together with LiAlO₂, spinel (MgAl₂O₄) acted as nuclei for the precipitation of BaAl₂O₄. The apparent activation energy of initial devitrified crystallization decreased from 314.16 KJ/mol (original slag) to 297.32 KJ/mol (5 wt% Al₂O₃ added) and 269.46 KJ/mol (10 wt% Al₂O₃ added). The crystallization ratio of the films also increased after adding extra Al₂O₃.