Thermodynamics and Phase Relationships of Transition Metal-Sulfur Systems: II. The Nickel-Sulfur System
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HIS is the second of a series of papers on the thermodynamics and phase relationships of transitionmetal sulfur systems. The first one concerns the thermodynamics and phase relationships of the cobalt- sulfur binary," This one concerns the same subjects of the nickel-sulfur binary. The Ni-S phase diagram as given in Hansen and Anderko ," Elliott,a Shunk,4 and the Metals Handbook" has been superseded by the one given by Craig and Scott," The major revision of the Ni-S phase diagram as given in Ref. 6 concerns the melting behavior of NiS z. While Elliott a and the Metals Handbook" report that NiS z melts congruently and forms a monotectic with the sulfur-rich liquid, Craig and Scott" report that NiS z melts synthetically. This major revision is based on the extensive investigation of Arnold and Maltk," Eight intermediate phases have been reported in the literature. Z-6 However, the present study, as to be discussed later, shows the previously reported high-temperature "NhSz" phase with a homogeneity range from 37 to 44 at. pet S actually consists of two intermediate phases. All nine phases with their crystal structures and designations are summarized in Table I. The crystal structure data are taken from Refs. 2 to 4 while the designations of these phases are those used in Ref. 5. The mineralogical names for some of these phases are taken from Craig and Scott," Rosenqvist," Nagamori and Ingraham" and Meyer, Warner, Rao and Kellogg,lO and Venal and Gieger l l measured the activity of sulfur in the liquid state while Rosenqvist," Laffitte/ z Rau/ a, l4 Line and Laffitte/ 5 and Leegaard and Rosenqvtst'" measured the activity of sulfur in the solid state. The experimental measurement of the present study on the "NhSz" phase was carried out by Lin'? as part of his R. Y. LIN, formerly Research Assisstant, Materials Department, College of Engineering and Applied Science, University of WisconsinMilwaukee, Milwaukee, WI, is now a Graduate Student, Department of Materials Science and Engineering, M.LT., Cambridge, MA. D. C. HU is Research Assistant, Materials Department, College of Engineering and Applied Science, University of Wisconsin-Milwaukee, Milwaukee, WI 53201. Y. A. CHANG is Professor, Materials Department, College of Engineering and Applied Science, and Associate Dean of Research, Graduate School, University of Wisconsin-Milwaukee, Milwaukee, WI 53201. Manuscript submitted October 12, 1977.
M.S. thesis. At the completion of his study, a paper by Rau l4 on the same subject was published. The objectives of the present paper are 1) to report our experimental data 2) to evaluate the data obtained by us as well as those available in the literature in order to obtain thermodynamic equations of state for all the Ni-S intermediate phases and 3) to present several forms of the Ni-S phase diagrams.
EXPERIMENTAL The experimental method has been described elsewhere.',17,18 In brief, a metal sample or a sulfide sample is equilibrated with a gas mixture consisting of HzS, Hz and argon at a given temperature. The activity of su
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