Thermodynamics of the [Ir-In] system

The molar enthalpy of formation of the [Ir-In] liquid alloys [Delta(mix)Hm degrees] corresponding to the reaction, at T-e and p degrees: a In-(liq) + b Ir-(liq) --> InxIr(1-x)(liq) was determined on the following temperature and molar fraction ranges 1175< T-e/K<1589 and 0<x<0.26 (where x is the iridium molar fraction x,,), respec tively, with a fully automated high temperature calorimeter. In these tempe rature and molar fraction ranges, the enthalpy of formation is negative and not temperature dependent. As for the other (TM-sp) binary systems previou sly studied, assuming suitable the Redlich-Kister relation, the enthalpy of mixing could be described as follows (in kJ.mol(-1)): Delta(mix)H(m)degrees = x.(1 - x)xi(y) with xi(y)=-74.27+/-18.51y+27.74 y(2)-15.28 y(3) and y=(x(1r)-x(1n)). In th is case, the coordinates of the minimum are estimated to be at Delta(mix)H( m)degrees=-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: Delta(mix)h(m)degrees (Ir supercooled liquid in infinity liq In) = -50+/-2 kJ.mol(-1). The integral and limiting partial enthalpies of mixing have been compared w ith the data predicted by Miedema and co-workers. The trend of the Delta(mi x)H(m)degrees=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 Ir In3 and IrIn2 are in equilibrium with the liquid phase. For three compositi ons (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 calculate d with the Neumann-Kopp law. The weak thermal effect appearing in the Cp de grees=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 (eu tectic, 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 cond ition,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 miscibi lity gap at high temperature could also be assumed for this last system. (C ) 2000 Elsevier Science S.A. All rights reserved.