New thermodynamic assessment of nickel–tin solid and liquid alloys

Standard enthalpies of formation, ΔfH°(298.15), entropies, S  °(298.15), and molar heat capacities, Cp,m°(298.15), for a number of phases of Ni–Sn system have been estimated by graphical and analytical methods. The ΔfH°(298.15), S  °(298.15) and Cp,m°(298.15) values of a new metastable NiSn9 compound were found equal to −85.0 ± 5 kJ mol−1, 420.7 ± 5 J K−1 mol−1 and 228 J K−1 mol−1, respectively. New, reassessed value of ΔfH°(298.15) for metastable NiSn was obtained equal to −54.0 ± 4 kJ mol−1. The limiting partial enthalpies of Ni in solid Sn (H¯lim(Ni)=−3±1 kJ mol−1) and Sn in solid Ni (H¯lim(Sn)=−49±4 kJ mol−1) at 298.15 K were determined by graphical method. The calculated Cp,m°(298.15) values of NiSn and Ni3Sn4 are equal 45.1 J K−1 mol−1 and 160.3 J K−1 mol−1, respectively. Using different methods, the standard entropy values S°(298.15) (NiSn) = 71.7 ± 2 and S°(298.15) (Ni3Sn4) = 256.4 ± 5 J K−1 mol−1 were calculated. It has been shown that the combined approach based on a modified quasi-chemical model and the Tsuboka–Katayama–Wilson's equations reproduce with good approximation the experimental data on the thermodynamic functions of mixing for liquid Ni–Sn alloys. This method takes into consideration the effects of the short range ordering and the temperature on the thermodynamic functions of mixing, and has the advantage that prior knowledge of experimental values of mixing quantities is not required. The extension of this approach to the binary systems, where volume effect is inherent, is motivated.