Thermodynamic assessment of the Zr-O binary system

Thermodynamic and phase diagram experimental data relevant to the Zr-O bina ry system have been assessed. A set of Gibbs energy functions describing th e phases in this system is presented. The adjustable parameters of the mode ls are obtained by least-squares fit to the experimental data. The liquid p hase is described by Hillert's partially ionic liquid model. The interstiti al solid solution model is applied to the metallic zirconium solid solution s beta Zr and alpha Zr. The ordering alpha Zr is described by a three-subla ttice model with Bragg-Williams treatment of ordering. The two modification s of the zirconium dioxide, alpha ZrO2 and beta ZrO2, are modelled as stoic hiometric phases. The modification gamma ZrO2 is described by the Wagner-Sc hottky model expressed in the compound-energy formalism. The gas phase is t reated as an ideal solution of the species Zr, Zr-2 O-1, O-2, O-3, ZrO and ZrO2. The calculated phase diagrams and values for the thermodynamic proper ties are compared with experimental data.