Interfacial tension decreases drastically when an intense chemical reaction occurs at a steel–slag interface. This phenomenon results in spontaneous droplet spreading during the initial period of reaction and droplet recovery as the rate of reaction decreases. In the present work, spreading tendency was found to be associated with spontaneous emulsification of both steel in slag and slag in steel. Spontaneous emulsification was observed at 1550°C when a liquid Fe–3.28%Al alloy droplet was placed in contact with liquid CaO–SiO2–Al2O3 (40:40:20 by weight) slag.
Surface turbulence induced metal emulsification and droplet spreading was observed by X–ray photography. Spontaneous droplet spreading was noted at alloy aluminium contents as low as 0.25%. Spontaneous emulsification was steel into slag was documented at aluminium contents greater than 3%. From the observation of quenched Fe–3.28%Al alloy droplets by optical and scanning electron microscopy, slag entrapment and metal emulsification were documented and the metal–slag interface was shown to be extremely perturbed during the reaction of aluminium with silica.