Heat capacity of hydrogenated Zircaloy-2 and high Fe Zircaloy

Heat capacities (Cp) of non-hydrogenated and hydrogenated Zircaloy-2 and high Fe Zircaloy were measured in the temperature range from 350 to 873 K, using a differential scanning calorimeter. The hydrogen concentrations in the two types of alloys ranged from 26 to 1004 ppm. The Cp values of the as-received alloys with 26–29 ppm hydrogen were in good agreement with literature data for low hydrogen Zircaloys. From this finding and observation of almost the same enthalpy changes for hydride dissolution for both alloys, it was concluded that there was no difference in Cp values between the two types of hydrogenated Zircaloys. The dissolution enthalpy of hydrides calculated from Cp data was 41.0 kJ/g-atom H. For Zircaloy-2 samples with higher hydrogen concentrations than 700 ppm, the phase transition from α+δ to α+β was observed at the eutectoid temperature of 824–827 K. Two types of models describing an additional heat capacity due to the hydride dissolution were presented based on the present Cp data and previously derived terminal solid solubility of hydrogen.