Effect of Fe2O3 on the size and components of spinel crystals in the CaO-SiO2-MgO-Al2O3-Cr2O3 system

The stability of chromium in stainless steel slag can be enhanced by increasing the spinel crystal size. The effect of Fe2O3 on the size of spinel crystals in the CaO-SiO2-MgO-Al2O3-Cr2O3 system was investigated using lab experiments carried out in a carbon tube furnace. Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) and X-ray diffraction (XRD) were used to analyze the microstructure, components, and the mineral phases of synthetic slags. FactSage 7.1 was used to calculate the crystallization process of the molten slag. The results showed that the addition of Fe2O3 promoted the precipitation of spinel crystals and inhibited the formation of dicalcium silicate. The size of spinel crystals increased from 2.74 to 8.10 mu m and the contents of chromium and iron in the spinel varied as the Fe2O3 addition was increased from 0 to 20wt%. Fe2O3 thermodynamically provided the spinel-forming components to enhance the formation of FeCr2O4, MgFe2O4, and Fe3O4. The addition of Fe2O3 increased the fraction of liquid phase in a certain temperature range and promoted diffusion by decreasing the slag's viscosity. Therefore, Fe2O3 is beneficial to the growth of spinel crystals in stainless steel slag.