The effect of the addition of alumina on the viscosity, surface tension, and foaming efficiency of 2.5(CaO/SiO2)-xAl2O3-yFeO-MgO melts

Abstract

Viscosity and surface tension strongly influence the efficiency of slag foam in metallurgical processes. An excellent foaming slag preserves heat and lowers the cost of smelting in an electric furnace. In this study, we investigated the viscosity, surface tension, and foaming efficiency of a 2.5CaO/SiO2-xAl2O3-yFeO-MgO slag. We also investigated the different valence oxygen ions by X-ray photoelectron spectroscopy (XPS). The results showed that with a gradual increase in the content of Al2O3, the viscosity initially increased and then decreased, and the changes in surface tension followed a similar pattern. The change in viscosity was caused by the increase in the degree of polymerization of the slag, which was determined by the competitive relationship between polymerization and the reduction in the stability of the overall network structure. Adding a small amount of Al2O3 to the slag slightly increased the number of Al–O–Al structures, whereas adding a large amount of the Al2O3 led to the formation of low-strength Al–O–Si structures, which reduced the stability of the network structure, thus reducing the viscosity. Because the surface tension is related to the concentration of non-bridging oxygens (NBOs), when the NBO content increased, the instability of the surface structure caused an increase in energy, thus increasing the surface tension. In addition, the CaO–SiO2–5MgO-xAl2O3-yFeO five-element oxide in this study had the lowest surface tension at the same NBO concentration, which positively contributed to slag foaming. Finally, When the Al2O3 content in the system increased from 5.1 to 15.7 wt%, the foaming efficiency increased from 24.2 to 69.2 (minute‧centimeters), an increase of 286%.