Crystallization Behavior of the CaO-Al₂O₃-MgO System Studied with a Confocal Laser Scanning Microscope

The crystallization behavior of a calcium-aluminate system with various MgO content from 2.5 to 7.5 wt pct and CaO/Al₂O₃ ratios between 0.8 and 1.2 has been examined using a confocal laser scanning microscope (CLSM). CCT (continuous cooling transformation) and time temperature transformation (TTT) diagrams were constructed to identify the primary crystal phase of slag at different compositions and at cooling rates between 25 and 800 K/minutes. In the slag at a CaO/Al₂O₃ ratio of 1.0, crystallization temperature increased during isothermal and continuous cooling with higher MgO content, and the shortest incubation time was observed at 5 wt pct MgO. When MgO content was fixed to be 5 wt pct, crystallization temperature increased with lower CaO/Al₂O₃ ratio. According to the slag composition, cooling rates and temperature, the primary phase could be CA, or C₅A₃, or C₃A, or C₃MA₂, or MgO, and the crystal morphology changes from dendrites to faceted crystals to columnar crystals in this composition range.