Фазовая диаграмма системы Ag-S

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Ag-S (Silver-Sulfur) R.C. Sharma and Y.A. Chang The Ag-S system is characterized by an intermediate phase, Ag2S, that forms at ~33.33 at.% S. Ag2S has three stable allotropic forms between room temperature and its congruent melting point of 842 C. The low-temperature form of aAg2S is essentially stoichiometric, whereas bAg2S and gAg2S can dissolve an excess of Ag as well as S. There are two liquid miscibility gaps in the Ag-S system, one each in the Ag- Ag2S and Ag2S-S subsystems. There is no experimental determination of the liquid miscibility gap in the Ag2S-S region. The assessed phase diagram is based on review of the literature [46Kra, 74Rau, 81Fuk]. Pure Ag and S melt at 961.93 and 115.22 C, respectively. S, in the solid state, exists in two allotropic forms, (aS) stable up to 95.5 C and (bS) stable from 95.5 C to its melting point at 115.22 C. The solubility of Ag in (aS) and (bS) has not been experimentally determined; however, it is expected to be negligible. At 100 to 200 C, aAg2S transforms to a different allotropic form, dAg2S, at higher pressures [37Bri]. The aAg2S = bAg2S transition temperature increases with pressure at the rate of ~1.5 с 0.2 C/kbar up to 12.3 kbar and 195 C, at which point a discontinuous change to 3.1 с 0.2 C/kbar occurs [70Cla]. 37Bri: P.W. Bridgman, Proc. Am. Acad. Arts Sci., 72, 45 (1937). 46Kra: F.C. Kracek, Trans. Am. Geophysical Union, 27(3), 364-374 (1946). 70Cla: J.B. Clark and E. Rapaport, J. Phys. Chem. Solids, 31, 247-254 (1970). 74Rau: H. Rau, J. Phys. Chem. Solids, 35, 1553-1559 (1974). 81Fuk: N. Fukatsu and Z. Kozuka, J. Jpn. Inst. Met., 45(12), 1263-1270 (1981) in Japanese. Published in Bull. Alloy Phase Diagrams, 7(3), Jun 1986. Complete evaluation contains 8 figures, 6 tables, and 34 references. Special Points of the Ag-S System