Effect of Oxide Fluxes on the Viscosity of Molten Aluminothermic Ferro-chrome Slags

Abstract

The viscous slag generated during aluminothermic reduction of metallic oxides for production of metals or alloys slows down the reduction process and obstructs clear separation of slag and metal. The fluxing constituents are added to bring down the viscosity. Hence the effect of variation of CaO and MgO contents on the viscosity of synthetically prepared ferrochrome slags having an approximate composition of industrial ferro-chrome slags resulting from aluminothermic reduction of chromium oxide has been studied at various temperatures. Increase of CaO and MgO contents is found to decrease the viscosity of the slags. The relative decrease in viscosity becomes very less beyond 40 mol% of CaO. It is further observed that both CaO and MgO additions do not decrease the viscosity appreciably at higher temperatures as they do at lower temperatures. The activation energy of viscous flow calculated from the viscosity data, is seen to obey the Arrhenius equation {m=A0exp(Em/RT). The activation energy, Em decreases with increased flux addition. It is also observed that the activation energy of viscous flow is independent of temperature but is a function of the composition of the slag. Within the range of compositions studied, the net-work breaking ability of Mg++ ion is not as high as that of Ca++ ion. The possible ionic structure of the liquid slags and ionic interactions have been discussed in light of the calculated values of activation energy of viscous flow. Al2O3 does not behave as an amphoteric oxide as it does in silicate melts.