STANDARD ENTHALPY OF FORMATION OF CU3AS AND HEATS OF MIXING IN THE LIQUID-SYSTEMS CU-AS AND FE-AS BY DIRECT COMBINATION HIGH-TEMPERATURE DROP CALORIMETRY

The standard enthalpy of formation of the congruent melting compound Cu3As (m.p. 1000 K) was determined by high temperature direct synthesis drop calorimetry in fused silica capsules at 1113 K. We found Delta H-f(degrees) (298 K)=-14.6+/-3.8 kJ mol(-1). Using our measured values of the heats of reaction of the process aAs(s)+bCu(s)-->cCu(1-x)As(x)(1) at 1113 K, we calculated the liquid-liquid enthalpies of mixing for three alloy compositions in Cu1-xAsx: x=0.235, 0.26 and 0.375. We carried out similar measurements at 1123 K for the eutectic alloy Fe1-xAsx(1) at x=0.24. The calorimetric results for the solid and liquid alloys are compared with predicted values from Miedema's semiempirical model.