THE COBALT-INDIUM SYSTEM - ENTHALPY OF FORMATION AND PHASE-DIAGRAM

With a fully automated, high-temperature calorimeter, the molar enthal py of formation of the [Co + In] liquid system was determined in the r egion 1080 K < T < 1765 K over a large mole fraction range. The molar enthalpy of formation of [Co + In] liquid alloys corresponding to the reaction, aCo(liq.) + bIn(liq.) = CoxIn1-x(liq.), with x = a/(a + b), is positive for all concentrations and may be expressed as: Delta(mix) H(m) degrees = x(Co)(1 - x(Co))[28.11 + 46.73x(Co) - 121.04x(Co)(2) 63.91x(Co)(3)] in kJ mol(-1). The values of the partial molar enthalpi es of cobalt and indium were determined and the limiting values were c alculated as Delta h(m) degrees(Co-liq. in infinity In-liq.) = +28.1 /- 2.0 kJ mol(-1) and Delta h(m) degrees(In-liq. in infinity Co-liq.) = + 17.7 +/- 5.0 kJ mol(-1). The shape of the graph Delta(mix)H(m) deg rees = f(x(Co)) obtained in the region 1528 K < T < 1765 K confirms th e existence of a liquid miscibility gap. A new position of the miscibi lity gap and the liquidus line on the In-rich side of the phase diagra m is proposed: the coordinates of the critical point are located at 0. 40 < x(In(cr)) < 0.45 and T-cr = 1770 +/- 5 K.