Wettability of Graphite by CaO-SiO2-Al2O3-FeO-MgO Slag

Abstract

Wettability of graphite by the CaO-SiO 2 -Al 2 O 3 -FeO-MgO slag has been investigated using the sessile drop technique. The focus of this paper is on the carbon/slag interfacial phenomena, which has a significant effect on the kinetics and mechanisms of iron reduction from the molten slag by carbon in the direct iron smelting process. In this study wettability of graphite by slags of different compositions has been investigated at 1600°C. Experiments were performed in a horizontal superkanthal tube furnace. Slag droplets on a graphite substrate were placed into the hot isothermal zone of the furnace and examined using a CCD camera. The camera assembly was connected to a video cassette recorder through a video distributor amplifier. The reaction sequence during the experiment was recorded on video tape. The images from the tape were converted into computer files and the wettability of graphite by slag was determined by direct measurement of the interfacial contact angle using a sophisticated computer software. An on-line date/time generator permitted image capturing as a function of time. The results indicated significant effect of slag composition on the slag/graphite interfacial interactions. The change in the wetting in the reactive system is predominantly affected by the Gibbs free energy of the reaction. In the initial moment, when iron oxide concentration is high, wetting is good. As the slag graphite system approaches equilibrium the effect of the reactive component decreases and wettability declines. The product iron formed as a result of the reduction reaction was seen to be deposited inside the graphite within a distance of 30-50 μm from the graphite/slag interface. In addition, lumps of iron are also deposited at the slag/graphite interface.