Thermodynamic assessment of the Fe-Te system. Part I: Experimental study

A thermodynamic description of the Fe-Te system needs to be developed in order to model internal corrosion by fission products in fuel pins of Generation IV nuclear reactors. In preparation for a thermodynamic assessment of the system, an experimental study has been performed in order to clarify some unknown or conflicting phase diagram data. New phase diagram data have been obtained using Differential Thermal Analysis and isothermal heat treatments followed by electron microscopy with EDS and WDS analysis. The DTA analysis revealed new phase boundary data, and confirmed a very steep Fe-rich liquidus, supporting the possibility of a liquid miscibility gap in the Fe-FeTe region. The analyses also confirmed the probable eutectoid reaction δ→β+δ' at 523 °C. The invariant arrests of the unknown γ phase were consistent with information available in literature, but the phase was not identified via XRD of samples at its postulated composition. However, metallography of the samples revealed an unexpected microstructure pertaining to the δ phase, which might be the γ phase, and is discussed in this paper. The monoclinic space group C2/m is proposed for the δ phase based on XRD. The collected data will be used together with that available in literature to perform a thermodynamic Calphad assessment in a subsequent paper Part II: Thermodynamic modeling.