Chemical zoning of calcium aluminoferrite formed during melt crystallization in CaO–SiO 2–Al 2O 3–Fe 2O 3 pseudoquaternary system

Abstract

In the CaO–SiO 2–Al 2O 3–Fe 2O 3 pseudoquaternary system, the solid solutions of Ca 2(Al x Fe 1− x ) 2O 5, with x<0.7 (ferrite), Ca 2SiO 4 (belite), Ca 3Al 2O 6 (C 3A) and Ca 12Al 14O 33 (C 12A 7), were crystallized out of a complete melt during cooling at 8.3 °C/min. Upon cooling to 1370 °C, both the crystals of ferrite with x=0.41 and belite would start to nucleate from the melt. During further cooling, the x value of the precipitating ferrite would progressively increase and eventually approach 0.7. At ambient temperature, the ferrite crystals had a zonal structure, the x value of which successively increased from the cores toward the rims. The value of 0.45 was confirmed for the cores by EPMA. The chemical formula of the rims was determined to be Ca 2.03[Al 1.27Fe 0.68Si 0.02] Σ1.97O 5 ( x=0.65). As the crystallization of ferrite and belite proceeded, the coexisting melt would become progressively enriched in the aluminate components. After the termination of the ferrite crystallization, the C 3A and belite would immediately crystallize out of the melt, followed by the nucleation of C 12A 7. The C 12A 7 accommodated about 2.1 mass% Fe 2O 3 in the chemical formula Ca 12.03[Al 13.61Fe 0.37] Σ13.98O 33, being free from the other foreign oxides (SiO 2 and P 2O 5).