Phase Formation Specifics in the High-Alumina Region of the СаО–Al2О3 System

Phase formation of calcium monoaluminate and calcium dialuminate in the СаО–Al₂О₃ system in the range 230–1450°C was studied using a model powder mixture comprising aluminum and calcium hydroxides. The onset of formation of an intermediate phase Ca₁₂Al₁₄O₃₃ (С₁₂А₇) was observed at 430°С. At 1100°С, the appearance of CaAl₄O₇ (CA₂) and the presence of κ-Al₂O₃ were observed. The onset of intense formation of the CaAl₂O₄ (СА) phase is at 1170°С. In the range 1250–1400°С, the CA amount increases notably, while the СА₂ proportion remains almost unchanged. The final formation of the CA and CA₂ target phases occurs in 2 h at 1450°С. The syntheses of CA and CA₂ is controlled by Ca²⁺ diffusion inward the aluminum-enriched cores of spherulites. Energy dispersive X-ray spectroscopy elucidated the CA and CA₂ distribution in the form of concentric layers.