A comparison study on the dissolution mechanism of Al2O3 inclusion on fluorine-bearing and fluorine-free molten mold fluxes
The dissolution mechanism of Al 2 O 3 inclusions in molten slags was explored by in-situ single hot thermocouple technique combined with X-ray photoelectron spectroscopy. Result shows that it takes 2940 s to completely dissolve Al 2 O 3 inclusions in the molten F-bearing mold flux, which is mainly controlled by boundary layer diffusion. Because the connected [AlO 6 ] octahedra in the Al 2 O 3 inclusion is gradually destroyed by the O 2− ions in the melt. By comparison, the CaO–SiO 2 –B 2 O 3 based F-free mold flux only takes 840 s to completely dissolve Al 2 O 3 inclusions. Because the [AlO 6 ] octahedra is destroyed and further transformed to [AlO 4 ] tetrahedra and produce O 2− ions, which greatly facilitates the dissociation of the Al 2 O 3 particle. However, the formed [AlO 4 ] tetrahedra will promote the precipitation of the dense 2CaO·SiO 2 ·Al 2 O 3 crystals, which tightly encases the Al 2 O 3 particle and causes significant drop in the dissolution rate. Thus, the dissolution rate is controlled by chemical reaction and then by boundary layer diffusion.
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