The Effects of Al2O3 and SiO2 on the Formation Process of Silico-Ferrite of Calcium and Aluminum (SFCA) by Solid-State Reactions

Abstract

The silico-ferrite of calcium and aluminum (SFCA) is a significant crystalline phase that bonds in high basicity sinter. Al2O3 and SiO2 play an important role in the formation of SFCA in the Fe2O3–CaO–SiO2–Al2O3 system, but the effect mechanism of Al2O3 and SiO2 on the formation of SFCA is unclear. To investigate this effect, sintering experiments were carried out with different temperatures and different times. It was found that the reaction of Al2O3 with CaFe2O4 (CF) as an initial product was easier to form during the calcium iron aluminum oxide (CFA) than that of SiO2 with CF to form SFC. This was due to the former directly forming to CFA while the latter initially formed Ca2SiO4 (C2S) and Ca2.5Fe15.5O25, and then SFC. It was also observed that when Al2O3 and SiO2 existed simultaneously, the Al2O3 initially reacted with CF to form CFA at 1100 °C, while the SiO2 participated in the formation of SFCA at 1150 °C without the formation of SFC. Moreover, it was understood that these were different effects in that the Al2O3 promoted the transformation from the orthorhombic crystal system to the triclinic crystal system, while the SiO2 dissolved into CFA to form the SFCA phase when Al2O3 existed.

Effect of impurity oxides on CWF (CaFe3O5) formation in lime magnetite pellets – part I: thermodynamic assessments and experimental investigations

“…In the context of iron ore agglomeration, SFCA (silico ferrites of calcium and aluminium) phases are highly studied due to their importance in determining the properties of iron ore sinters. The SFCA formation begins with the reaction of Fe 2 O 3 and CaO in the sequence of dicalcium ferrite (C 2 F) → calcium ferrite (CF) → calcium diferrite (CF 2 ) formation, followed by formation of complex ferrites above 1200°C through reaction of SiO 2 and Al 2 O 3 impurities in the ore to form SFC (silico ferrites of calcium) and CFA (calcium iron aluminium oxide) phases prior to SFCA formation [13][14][15][16][17][18][19][20][21]. A recent article by Liao and Guo suggested that CFA formation was easier compared to SFC because SiO 2 forms dicalcium silicate (Ca 2 SiO 4 ) phase upon reaction with CF [21].…”

Effects of Basicity and Al₂O₃ Content on the Crystal Structure of Silico-ferrite of Calcium and Aluminum

“…Webster et al used in-situ synchrotron XRD to conduct a series of studies on the mechanisms of SFCA formation in iron ore sinter at high temperatures [23][24][25][26][27][28][29][30] . Furthermore, Takayama et al used Rietveld analysis to conduct QPA of iron ore sinter obtained from pot tests 6) , and Liao and Guo used it to analyze the solid-state reaction mechanism of SFCA 31) . Recently, we demonstrated that Rietveld analysis can also be applied to QPA for identifying site occupancy 7) .…”

Study of SFCA and SFCA-I Phase in the Ternary Phase System of Iron Ore Pellets

“…As we have seen that on increasing the hematite phase grain density and silicate phase grain density the CCS value also increases. On increasing the pore phase grain density the CCS value is decreased [13][14][15][16].…”