New thermodynamic assessment of nickel–tin solid and liquid alloys

Abstract

Standard enthalpies of formation, Δ f H°(298.15), entropies, S°(298.15), and molar heat capacities, C p , m ° ( 298.15 ) , for a number of phases of Ni–Sn system have been estimated by graphical and analytical methods. The Δ f H°(298.15), S°(298.15) and C p , m ° ( 298.15 ) values of a new metastable NiSn 9 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 Δ f H°(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 mo l − 1 ) and Sn in solid Ni ( H ¯ lim ( Sn ) = − 49 ± 4 kJ mo l − 1 ) at 298.15 K were determined by graphical method. The calculated C p , m ° ( 298.15 ) values of NiSn and Ni 3Sn 4 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) (Ni 3Sn 4) = 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.