Enthalpy measurements of the solid high-temperature β-phase and the liquid phase of hafnium (3 wt.% Zr) by levitation drop calorimetry

The molar enthalpy, ΔH, of hafnium (3 wt.% Zr) has been measured by levitation drop calorimetry for the solid β-phase in a temperature range from T=2096 to 2455 K and for the liquid phase from T=2339 to 2988 K. The temperatures of the α to β and the β to liquid transition of this material are 2012 and 2471 K, respectively. The enthalpies obtained are represented by the following enthalpy-temperature functions:Solid β-Hf ΔH/J mol−1=−8299+31.79 T/K+1.42×10−3 T2/K2.Liquid Hf ΔH/J mol−1=99171+37.51(T−2471)/K.The experimental values scatter within a relative error of ±4.8%. The average deviation between the values and the curves given by the two functions is ±1.06% for the measurements on the solid phase and ±1.27% for the liquid phase. The resulting values for the enthalpy of fusion, ΔfusH, and the entropy of fusion, ΔfusS, are 20.247±2.1 kJ mol−1 and 8.19 J mol−1 K−1, respectively. The results are compared with enthalpy estimates given in the literature where only two experimental data points are available for the solid β-phase.