When molten slag exits a furnace, it can exceed 1,400–1,600 °C depending on the process. At these temperatures the slag is a highly fluid mixture of silicates, oxides, and minor metal compounds. If it cools slowly, the material has time to crystallize, forming dense mineral phases such as calcium silicates and iron-bearing compounds. By directing compressed air jets onto the molten stream or slag bed, engineers dramatically increase the convective heat transfer coefficient. The air flow strips heat from the surface, accelerating solidification and promoting the formation of a vitreous (glassy) microstructure instead of a fully crystalline one. This rapid quenching serves several purposes: • Microstructural control – Fast cooling suppresses crystal growth and increases the proportion of amorphous phases. • Improved grindability – Glassy slag fractures more easily during milling, reducing energy consumption in downstream processing. • Enhanced cementitious reactivity – Amorphous calci...