Calorimetric determination of the δ hydride dissolution enthalpy in ZIRCALOY-4

Abstract

In this work, the dissolution enthalpy of the delta hydride phase in the alpha Zr matrix in Zircaloy–4 has been determined with a differential scanning calorimeter (DSC) in two different ways: by means of a van´t Hoff equation, measuring the terminal solubility temperature in dissolution, TSSd, and by direct measurement of the dissolution heat as the area between the base line and the calorimetric curve. The application of the DSC technique to the hydride dissolution heat measurements, a transformation which covers an extended temperature range, is completely original and requires a special treatment of the calorimetric curve. These measurements were done on samples which practically cover the whole solubility range of hydrogen in alpha Zr phase (80–640 ppm). The values obtained, 36.9 kJ/mol H and 39.3 kJ/mol H respectively, are self–consistent and in good agreement with the values of the more recent revisions, but reduces considerably the scatter of the literature data.