Crystallization Behavior of Synthesized CaO‐Al 2 O 3 ‐Sc 2 O 3 Rare Earth‐Containing Slag

ABSTRACT This study investigates the crystallization behavior of CaO‐Al 2 O 3 ‐Sc 2 O 3 ternary synthetic slags to determine the effects of Sc 2 O 3 content (4–14 wt.%) and CaO/Al 2 O 3 ratios (0.54–1.32) on crystal formation. High‐temperature thermodynamic experiments, combined with scanning electron microscopy (SEM) and energy‐dispersive spectroscopy (EDS), were employed to analyze the crystallization kinetics of Sc 2 O 3 and CaSc 2 O 4 in isothermal and non‐isothermal processes using the Johnson‐Mehl‐Avrami‐Kolmogorov (JMAK) theory. In situ observations via high‐temperature confocal laser scanning microscopy (HT‐CLSM) within 1173–1873 K revealed that increasing the CaO/Al 2 O 3 ratio (at fixed 14 wt.% Sc 2 O 3 ) or elevating Sc 2 O 3 content (at CaO/Al 2 O 3 = 1.32) significantly enhanced Sc 2 O 3 crystallization. The area fraction of the Sc 2 O 3 phase reached up to 27.5% under optimal conditions (cooling rate = 1 K/min, holding time = 60 min, CaO/Al 2 O 3 = 1.34, Sc 2 O 3 content = 14 wt.%). Slower cooling rates and prolonged holding times further promoted crystalline phase formation. HT‐CLSM analysis identified distinct phase transitions: amorphous Sc 2 O 3 nucleation initiated at 1819 K, while CaSc 2 O 4 crystallization began at 1699 K and reached completion at 1618 K. These findings provide critical insights into optimizing slag systems for efficient scandium recovery.