Experimental investigation and thermodynamic modelling of the Ag-Zr system

After reviewing existing studies and conducting a new experimental investigation on the Ag-Zr phase diagram, a new CALPHAD model for the Ag-Zr system is presented. These experiments include, differential thermal analyses over the whole composition range, silver activity measurements and a determination of the standard enthalpy of formation of AgZr by calorimetry. The discussion about how AgZr and AgZr 2 decompose is resolved, showing congruent melting and peritectic decomposition, respectively. The model accurately reproduces the phase diagram, but more experiments are needed for the liquidus and solidus of β(Zr), especially in zirconium-rich areas. It is noteworthy that sub-stoichiometric yttria crucibles have been successfully tested in this study with melts containing metallic zirconium. The model matches measured silver activities well, giving confidence in the estimated enthalpy of formation of compounds, which were previously thought to be not exothermic enough in other models. The calculated enthalpy of formation for AgZr fits within the experimental uncertainty range. Future experiments on the heat capacities of intermetallic compounds could further improve the Ag-Zr system model.