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

The molar enthalpy, DeltaH, of hafnium (3 wt.% Zr) has been measured by lev itation drop calorimetry for the solid P-phase in a temperature range from T = 2096 to 2455 K and for the liquid phase from T = 2339 to 2988 K. The te mperatures of the alpha to beta and the beta to liquid transition of this m aterial are 2012 and 2471 K: respectively. The enthalpies obtained are repr esented by the following enthalpy-temperature functions: Solid beta -Hf DeltaH/J mol(-1) = -8299 + 31.79 T/K + 1.42 x 10(-3) T-2/K-2 . Liquid Hf DeltaH/J mol(-166) = 99171 + 37.51(T-2471)/K. The experimental values scatter within a relative error of F 4.5%. The aver age deviation between the values and the curves given by the two functions is +/- 1.06% for the measurements on the solid phase and +/- 1.275 for the liquid phase. The resulting values for the enthalpy of fusion, Delta H-fus, and the entropy of fusion, Delta S-fus, are 20.247 +/- 2.1 kJ mol(-1) and 8.19 J mol(-1) K-1, respectively. The results are compared with enthalpy es timates given in the literature where only two experimental data points are available for the solid beta -phase. (C) 2001 Elsevier Science B.V. All ri ghts reserved.