Wetting Behavior of TiO₂ by Calcium Ferrite Slag at 1523 K

The wetting behaviors of a TiO₂ substrate by calcium ferrite (CF) series slags were investigated using an improved sessile drop method at 1523 K (1250 °C). The initial contact angles were in the range 35 to 50 deg, the final equilibrium apparent contact angles were < 20 deg, and the spreading durations were in the range 75 to 180 seconds. The CF-TiO₂ system showed reactive wetting, which was categorized into four dynamic stages. Stage I: physical spreading, stage II: slow linear spreading, stage III: fast linear spreading, and stage IV: equilibrium. Interfacial reactions yielded CaTiO₃ during reactive spreading, thereby transitioning TiO₂ wetting into CaTiO₃ wetting and then forming Fe₂TiO₅ and FeTiO₃ owing to the excess Fe₂O₃ and FeO that had accumulated in the interfacial zone. Although stage III spreading was faster than stage II spreading, adding MgO to the slag slowed stage III spreading. The interfacial microstructure of the residual slag was roughly divided into three layers owing to the different densities of the slag and solid products. The top layer was composed of CaTiO₃ and Fe₂O₃, the middle one was composed of CaTiO₃ and Fe₂TiO₅, and the bottom one was composed of Fe₂TiO₅ and FeTiO₃. Adding TiO₂ to the slag produced a dense CaTiO₃-containing interfacial layer, resulting in CF being detected in the residual slag.