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Thermochemical and topological studies of systems constituted by transition metals (Co, Ni) with Sn and Bi

Abstract : The aim of the thesis is to explore some thermochemical properties (enthalpies of formation, ) and phase equilibria in prospective Sn and Bi based lead-free solders alloyed with transition metals (Ni, Co) often used as metal substrates in the electronics. Numerous calorimetric experiments were done, using Setaram–Calvet 800C and Gachon apparatus. Other modern techniques as differential scanning calorimetry, differential thermal analyses (DTA), electron microprobe analyses, and X-ray diffraction were largely applied. The CALPHAD method was used for the optimization of the Co-Sn phase diagram.

Co-Sn system.
Direct reaction calorimetry was used to determine the enthalpy of formation of the compounds Co3Sn2, CoSn, CoSn2 and CoSn3 at 1287, 1033, 629 and 605 K, and of the liquid phase at 1010 and 1303 K. Drop solution calorimetry was used for measuring the enthalpy of formation of the liquid phase at 991 and 1020 K.
Feeble negative enthalpies of formation are found for the liquid phase at 991, 1010 and 1020 K, independently of the experimental technique, while positive values are registered at 1303 K. The willingness of the system Co-Sn to form metastable phases is confirmed. The transition temperatures between the respective low and high-temperature forms of Co3Sn2 and CoSn3 were verified by DTA.

Ni–Sn system.
The enthalpies of formation of Ni–Sn compounds (Ni3Sn_HT, Ni3Sn_LT, Ni3Sn2_HT, Ni3Sn2_LT and Ni3Sn4) were measured by direct reaction calorimetry at 1332, 943, 1288, 728 and 846 K. No thermochemical information is available in the literature for the latter two compounds. The transition temperature and enthalpy between low and high-temperature forms of Ni3Sn2 were verified by DTA.

Ni–Sn–Bi system.
The phase equilibria in the system Ni–Sn–Bi were studied at 733, 773, 903 and 1273 K and isothermal sections were constructed. A formerly unknown ternary compound with approximate formula Ni6Sn2Bi was found. Measurements of the enthalpy of formation were done at 733 and 1273 K (solid phases); at 833, 873 and 933 K (liquid phases).
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Submitted on : Thursday, July 12, 2007 - 10:58:37 AM
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Kristina Lilova. Thermochemical and topological studies of systems constituted by transition metals (Co, Ni) with Sn and Bi. Material chemistry. Université Henri Poincaré - Nancy I, 2007. English. ⟨tel-00162011⟩

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