Thermodynamics of the [Rh–In] system

Abstract

The molar enthalpy of formation of the [Rh–In] liquid alloys [Δ mix H m °] corresponding to the reaction, at T e and p°: a In ( liq) +b Rh ( liq) → In x Rh (1−x)( liq) was determined for the following temperature and molar fraction ranges 1250< T e/K<1670 and 0< x<0.30 (with x= x Rh), respectively, with a fully automated high temperature calorimeter. This function, negative and independent of temperature within the experimental error, can be described by the following Redlich-Kister equation (in kJ.mol −1): Δ mix H ° m =x.(1−x)ξ(y) with ξ( y)=−154.32−52.02 y+26.55 y 2+29.80 y 3 and y= x Rh− x In. The coordinates of the minimum are located at Δ mix H m °=−40±4 kJ.mol −1 and x=0.56 5. The limiting partial molar enthalpy of mixing of rhodium, deduced from experiments performed at 1155 K, is: Δ mix h ° m ( Rh supercooled liquid in ∞ liq In )=−106±5 kJ.mol −1 . By extrapolation of the ξ-function to x=1, the limiting enthalpy of In in supercooled liquid Rh was predicted with a larger uncertainty: Δ mix h ° m ( In liq. in supercooled liquid Rh )=−150±3 kJ.mol −1 . From these calorimetric experiments, some points of the equilibrium phase diagram were obtained. Thus the first shape of the liquidus of the [Rh–In] system (in the In-rich region) has been proposed. The integral and limiting partial enthalpies of mixing have been compared with (i) the predicted Miedema et al. values, (ii) with the data previously obtained for the (TM–In) systems. As for the systems previously studied, a transfer of electrons from indium towards rhodium is suggested to explain the negative enthalpy of formation of the [Rh–In] liquid system.