DFT validation of thermodynamic modeling and phase relations of equilibrium experimentation on the pseudo-ternary system Al2O3–CaO–Cr2Ox

Abstract

Despite great potential in several applications, the pseudo-ternary system Al2O3–CaO–Cr2Ox is an overlooked phase diagram due to the formation of a few toxic, carcinogenic, and water-soluble Cr6+ compounds. In the research paper, equilibrium experimentation of selected compositions was conducted at 1073, 1373, and 1673 K and investigated using XRD, SEM-EDS, and leaching tests. Further, thermodynamic modeling of limited databases of the pseudo-ternary system Al2O3–CaO–Cr2Ox was validated using DFT calculations. Including the recently discovered novel phase CaAl2Cr2O7 (wuboraite), the seven phases not available in the SGTE SUBstance (SSUB) database, along with the CaCrO4 and CaCr2O4 phases existing therein, were modeled using Density Functional Theory (DFT). Based on the above experiments and the present CALPHAD model, we have calculated the isothermal sections (1073, 1373, and 1673 K) of the Al2O3–CaO–Cr2Ox system for different oxygen partial pressures (P(O2)= 0.21 atm and P(O2)= 10−8 atm).