Thermodynamics of the [Ir–In] system

Abstract

Abstract The molar enthalpy of formation of the [Ir–In] liquid alloys [ΔmixHm°] corresponding to the reaction, at Te and p°: a In (liq) +b Ir (liq) → In x Ir (1−x) (liq) was determined on the following temperature and molar fraction ranges 1175 Δ mix H m °=x.(1−x)ξ(y) with ξ(y)=−74.27+18.51y+27.74 y2−15.28 y3and y=(xIr−xIn). In this case, the coordinates of the minimum are estimated to be at ΔmixHm°=−19±1 kJ.mol−1 and x=0.45±0.01. The limiting partial molar enthalpy of mixing of iridium, deduced from experiments performed at 1154 K, is: Δ mix h m ° ( Ir supercooled liquid in ∞ liq In)=−50±2 kJ.mol −1 . The integral and limiting partial enthalpies of mixing have been compared with the data predicted by Miedema and co-workers. The trend of the ΔmixHm°=f(x) diagrams obtained at the lower temperature (below 1175 K and between 1200 and 1300 K) allow us to conclude that the solid phases IrIn3 and IrIn2 are in equilibrium with the liquid phase. For three compositions (x=0.186, 0.25 and 0.33), the molar heat capacities have been measured between 423 and 763 K. These results are compared with the values calculated with the Neumann-Kopp law. The weak thermal effect appearing in the Cp°=f(T) graph with the alloy x=0.186 can be due to a change of structure. So, some information concerning the [Ir–In] equilibrium phase diagram (eutectic, peritectic and liquidus temperatures) was obtained. Thus, in the In-rich region, a preliminary shape of the liquidus of the [Ir–In] system has been proposed. Finally, thermodynamic results obtained under the same condition, on the one hand, for the Co–In system and, on the other hand, for the Ir–In system, have been compared: the existence of a liquid–liquid miscibility gap at high temperature could also be assumed for this last system.