The Phase Diagram of a CaO-Al2O3-VOx Slag System under Argon Atmosphere at 1500 °C

Abstract

The thermodynamic properties of the CaO-Al2O3-VOx slag system are of great significance to the direct alloying of vanadium in the smelting process of vanadium steel. In this paper, the phase equilibrium relationship of the CaO-Al2O3-VOx system under argon atmosphere at 1500 °C was studied with a high-temperature phase equilibrium experiment. Combined with SEM-EDS, XRD, and XPS, the types and compositions of each phase of the equilibrium slag samples and the content of different valence states of the vanadium element were determined. The result shows that under argon atmosphere (p(O2) = 10−3 atm) at 1500 °C, the CaO-Al2O3-VOx slag system contains four three-phase regions, seven two-phase regions, and a single-phase region (glass phase). The phase equilibrium results were plotted in a CaO-Al2O3-V2O5-VO2 spatial phase diagram, and the phase equilibrium results were projected on the CaO-Al2O3-V2O5 and CaO-Al2O3-VO2 pseudo-ternary phase diagrams, respectively. In the end, the rationality of projecting the phase equilibrium results to the pseudo-ternary phase diagram was quantitatively evaluated.