Partial and integral enthalpy of molten Ag-Al-Cu alloys

The partial and integral enthalpies of mixing of molten, ternary Ag-Al-Cu alloys were determined at 1146 K using a calorimeter of the Tian-Calvet type. Measurements were performed starting from pure Al to about 40 at.% Al along three sections with Ag:Cu ratios of about 1:3, 1:1 and 3:1. The values of the partial enthalpies of Cu, hCu ? -40 kJ mol-1, are rather constant from 1>xA1>0.6. The values of the partial enthalpies of Ag decrease from hAg = +5 kJ mol-1 to -10 kJ mol-1. The minimum values at about 40 at.% Al for the integral molar enthalpy are -18 kJ mol-1 for Cu:Ag=3:1, -12.5 kJ mol-1 for Cu:Ag=1:1 and -8,5 kJ mol-1 for Cu:Ag=1:3; the error is ‘5%. This behaviour is in agreement with the concept of Fermi enthalpy and corresponds to a transfer of one electron from aluminium to the not fully occupied bands of copper and silver, respectively. The existence of a ternary liquid non-stoichiometric compound with a very broad range of stability is claimed for alloys with about 0