Stability of Interface Between Liquid Steel and Molten Slag

Macroscopic flow near the metal-slag interface as well as the microscopic interfacial flow (Marangoni flow) generates shear forces at the interface. Depending on the local flow velocity and the physical properties of both liquid phases, the interface can become unstable and the phases are dispersed in each other. Emulsion is a disperse system of immiscible liquid phases in which the small droplets of the disperse phase exist in the continuous phase (dispersion medium). From the thermodynamic point of view, emulsions are not stable and separate with time. The process of separation is accompanied by the coagulation of the dispersed droplets. The electrochemistry on interfaces plays a crucial role in the emulsification process and in the stability of the emulsion. In the first steps of the process metallurgy, the emulsification processes increase the reaction rate by the enlargement of the interfacial area. In the last step, in the casting and solidification process, the emulsification of slag in liquid metal generates defects in the cast products and has to be avoided.