Bubble generation in refractory porous plugs: The role of the ceramic surface composition

Porous ceramic plugs are refractory devices applied in the steel ladle to inject gas bubbles into the liquid metal, aiming at its chemical and thermal homogenization, and the removal of non-metallic inclusions. Regarding its wear and corrosion resistance, the plug composition typically exhibits a low wettability by liquid steel to limit its infiltration into the porous structure. However, an additional aspect for the performance of plugs is their ability to control the size of the generated bubble, maximizing the likelihood of capturing inclusions. Based on the importance of this process to attain high-performance materials, this work studied the injection of gas into liquid media through ceramic capillary structures, focusing on the influence of the pore diameter and the contact angle upon the size of the generated bubble. The available models in the literature were analyzed and compared to the experimental results for a water-air system. As an outcome, a shape-corrected model for bubbling is proposed highlighting the region where the material dominates over the pore diameter to dictate the bubble size. Extending the model to the steel ladle, the results suggest the composition of the ceramic plug's surface as a key aspect to improve the cleanliness of the molten steel.