Effect of FeO concentration on the crystallization of high-temperature CaO - Al₂ O₃- MgO - FeO melts

Continuous cooling transformation (CCT) and time-temperature transformation (TTT) diagrams were plotted for CaO-Al₂O₃-MgO-FeO melts, and the morphology of the primary crystals formed was determined with a confocal laser scanning microscope (CLSM). When the CaO/Al₂O₃ ratio is 1.0, the crystallization temperature and incubation time increase with increasing MgO content. The TTT curve at 7.5 mass% MgO has a "C" shape, which facilitates the formation of amorphous phases. However, increasing the FeO content accelerated the crystallization time and lowered the crystallization temperature. The solidified melt with an FeO content of less than 10 mass% was a combination of the C₃MA₂ and C ₅A₃ phases; higher FeO content led to the formation of a secondary phase of Ca₂FeAlO₅ and CA following the precipitation of the C₃MA₂ primary phase. In addition, kinetic evaluation of the crystal growth with confocal micrographs indicated that the calculated crystal volume agreed well with the Johnson-Mehl-Avrami sigmoidal curve fit.