Thermodynamic assessment of the V–O system

Abstract

The V–O system was thermodynamically assessed using the CALPHAD method. The available experimental data on thermodynamic and thermochemical properties as well as phase diagram information were critically examined and a self-consistent set of thermodynamic parameters was obtained. In total 20 phases were included in this binary system. Five among them were treated as solid solution phases within the framework of the compound energy formalism. The halite phase was modeled as (V,V+2,V+3,Va)1(O−2,Va)1 covering the solubility of both V and O. Thermodynamic descriptions of two different models for the corundum phase are presented, one of which is more complex to correctly take the defect mechanisms into account. The liquid phase was described by the ionic two-sublattice model with the formula (V+2)P(O−2,Va−Q, VO1.5,VO2, VO2.5)Q. The stoichiometric Magnéli phases VnO2n−1 (n is an integer between 4 and 8) were modeled as (V+3)2(V+4)n−2(O−2)2n−1. Using the present thermodynamic description reliable experimental phase diagram, thermodynamic and thermochemical data were well reproduced.