Relationship between composition and structure of globules in narrow fractions of ferrospheres

In the general dependence of the ferrosphere composition, there are two regions differing in the properties of the melt from which the ferrospheres are formed. In a wide range of the Fe2O3 content variations from 30 to 79 wt.%, the behavior of the melt is determined by the properties of the FeO-SiO2-Al2O3 system. This system is characterized by the formation of an aluminum-magnesium-ferrite spinel. The content of the spinel increases with increasing iron concentration, and the unit cell parameter of the spinel also increases in the range from 8.3440 to 8.3897 Å. The unit cell parameters of the α-Fe2O3 phase are substantially smaller than those of stoichiometric hematite. For a higher Fe2O3 content (>83 wt.%) and a low Al2O3 content (<2 wt.%), the behavior of the melt is determined by the properties of the FeO-CaO system. This system is characterized both by the formation of the CaO-promoted ferrospinel, which has the unit cell parameter exceeding the corresponding parameter of stoichiometric magnetite, and by the formation of the hematite phase with the unit cell parameters close to those of stoichiometric α-Fe2O3. An increase in the iron concentration and the modulus of basicity leads to a decrease in the viscosity of the melt from which the ferrospheres are formed. In this case, the main morphological type of ferrospheres changes in the following sequence: porous (foam-like), glass-like, fine-grained (dendritic and point), skeletal-dendritic and coarse-grained (block-like).