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Phase stability and structural properties of Ni7 ± δS6 and Ni9S8 Heat capacity and thermodynamic properties of Ni7S6 at temperatures from 5 K to 970 K and of Ni9S8 from 5 K to 673 K

✍ Scribed by Svein Stølen; Helmer Fjellvåg; Fredrik Grønvold; Helene Seim; Edgar F. Westrum Jr.

Publisher
Elsevier Science
Year
1994
Tongue
English
Weight
414 KB
Volume
26
Category
Article
ISSN
0021-9614

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✦ Synopsis

Two stable solid phases with composition in the range from ( 45 to 48 ) moles per cent of (\mathrm{S}) exist for (nickel + sulfur): (\mathrm{Ni}{9} \mathrm{~S}{8}) which disproportionates to (\mathrm{Ni}{1-\delta} \mathrm{S}) and (\mathrm{Ni}{7_{ \pm}} \mathrm{S}{6}) above (T=) ((709 \pm 5) \mathrm{K}), and (\mathrm{Ni}{7}{ }{5} \mathrm{~S}{6}). The latter non-stoichiometric phase forms eutectoidally from (\mathrm{Ni}{9} \mathrm{~S}{8}) and (\mathrm{Ni}{3} \mathrm{~S}{2}) at (T=(675 \pm 3) \mathrm{K}). It is stable in a rather narrow temperature interval and disproportionates to (\mathrm{Ni}{1-\delta} \mathrm{S}) and (\mathrm{Ni}{3 \pm \delta} \mathrm{S}{2}) at (T=(850 \pm 2) \mathrm{K}). The phases are characterized structurally, and a revised phase diagram is presented. The heat capacity of a sample with composition (\mathrm{Ni}{7} \mathrm{~S}{6}) was determined over the temperature range (T=5 \mathrm{~K}) to (970 \mathrm{~K}) by adiabatic calorimetry. Effects from metastable modifications of the high-temperature phase were observed during thermal analysis, X-ray diffraction, and calorimetry on incompletely equilibrated samples. Thermodynamic-function values for (\mathrm{Ni}{7} \mathrm{~S}{6}) and (\mathrm{Ni}{9} \mathrm{~S}_{8}) are presented.

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