Standard molar enthalpies of formation of alloys in the pseudobinary system Zr(Al_xCo_1-x)₂ at the temperature 298.15 K

The standard molar enthalpies of formation Δ_fH_m^o of alloys with compositions in the pseudobinary system Zr(Al_xCo_1-x)₂Zr have been determined by solution calorimetry in a mixture of hydrofluoric and nitric acids. The values of Δ_fH_m^o(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: Δ_fH_m^o{Zr(Al_xCo _1-x)2}≈x·Δ_fH_m ^o(ZrAl₂)+(1-x)·Δ_fH _m^o(ZrCo₂).