Standard Molar Enthalpies of Formation of Alloys in the Pseudobinary System Zr(AlxCo1-x)2 at the Temperature 298.15 K.

Abstract The standard molar enthalpies of formation ΔfHm° of alloys with compositions in the pseudobinary system Zr(AlxCo1 − x)2Zr have been determined by solution calorimetry in a mixture of hydrofluoric and nitric acids. The values of ΔfHm°(298.15 K) obtained are as follows: −(113±11) kJ mol−1 for x=0; −(123±8) kJ mol−1 for x= 1 12 ; −(120±8) kJ mol−1 for x= 1 6 ; −(130±7) for x= 1 4 ; and −(147±10) kJ mol−1 for x= 1 2 . Uncertainties correspond to twice the standard deviation of the mean. The following empirical relation was found to be applicable over the range of compositions studied: ΔfHm°{Zr(AlxCo1 − x)2} ≈ x·ΔfHm°(ZrAl2)+(1 − x)·ΔfHm°(ZrCo2).