Heat capacity measurement of ZrOx and (Zr1−yNby)Ox from 325 TO 905 K

Abstract

Heat capacities of zirconium-oxygen alloys, ZrOx (x=0.17, 0.20, 0.28 and 0.31), and those of niobium doped alloys, (Zr1−yNby)Ox (x=0.17 and 0.28, y=0.005 and 0.01), were measured from 325 to 905 K by an adiabatic scanning calorimeter. Two kinds of heat capacity anomalies were observed for all samples. The anomaly at higher temperatures was assigned to be due to an order-disorder rearrangement of oxygen atoms. Another anomaly at lower temperatures was due to a non-equilibrium phenomenon. The entropy change due to the order-disorder transition for Zr-O solid solution at higher temperature obtained from this experiment was compared with the theoretical value. The transition temperature, transition enthalpy and entropy changes due to the order-disorder transition decreased with increasing niobium contents, indicating that arrangement of oxygen atoms in lower temperature phase may be partially disordered by the interaction between niobium and oxygen atoms.