Changes in the Phase Composition of Calcium Aluminoferrites Based on the Synthesis Condition and Al₂O₃/Fe₂O₃ Molar...

The presented work concerns the study of the changes in the phase composition of calcium aluminoferrites which depend on the synthesis conditions and the selection of the Al₂O₃/Fe₂O₃ molar ratio (A/F). The A/F molar ratio extends beyond the limiting composition of C₆A₂F (6CaO·2Al₂O₃·Fe₂O) towards phases richer in Al₂O₃. An increase in the A/F ratio above unity favours the formation of other crystalline phases such as C₁₂A₇ and C₃A, in addition to calcium aluminoferrite. Slow cooling of melts characterised by an A/F ratio below 0.58, results in the formation of a single calcium aluminoferrite phase. Above this ratio, the presence of varying contents of C₁₂A₇ and C₃A phases was found. The process of rapid cooling of the melts with an A/F molar ratio approaching the value of four favours the formation of a single phase with variable chemical composition. Generally, an increase in the A/F ratio above the value of four generates the formation of a calcium aluminoferrite amorphous phase. The rapidly cooled samples with compositions of C_22.19A_10.94F and C_14.61A_6.29F were fully amorphous. Additionally, this study shows that as the A/F molar ratio of the melts decreases, the elemental cell volume of the calcium aluminoferrites decreases.