Study on order-disorder transition of ZrO alloys (O/Zr = 0−0.31) by heat capacity measurement

Abstract

Heat capacities of ZrO alloys (O/Zr = 0, 0−10, 0.31 and 0.24) were measured from 325 to 905 K using an adiabatic scanning calorimeter. Two types of heat capacity anomalies were observed for all samples except pure zirconium metal. A heat capacity anomaly at lower temperature was attributed to a non-equilibrium phenomenon. Another heat capacity anomaly at higher temperature was assigned to an order-disorder rearrangement of interstitial oxygen atoms in zirconium host lattices. The enthalpy and entropy changes due to the order-disorder transition were determined from heat capacity data on the basis of the baseline which was obtained as the sum of harmonic, dilatometric, electronic and anharmonic terms. The experimental entropy changes of the order-disorder transition for ZrO 1 6 (α″ 1) and ZrO x ( α″ 2) phases were compared with the theoretical values. A new phase diagram of the ZrO system was proposed from the transition temperatures, transition enthalpy and entropy changes as a function of the O Zr ratio which were obtained in this study and in our previous work.