Фазовая диаграмма системы Li-S

К оглавлению: Другие диаграммы (Others phase diargams)

Li-S (Lithium-Sulfur) H. Okamoto The assessed phase diagram for the Li-S system is based on [72Cun] and [72Sha]. Only one compound, Li2S, exists in this system. No solubility of S in either form of (Li) is known. The L to (bLi) transformation in alloys may be eutectic, because [72Cun] observed that the transformation temperature is slightly lower than the melting point of pure bLi. However, the temperature difference may be within experimental uncertainty. Consequently, the transformation temperature in the assessed diagram is shown tentatively at the melting point of bLi. The melting point of Li2S is 1372 C [72Cun], which is within the range 1365 с 10 C reported by [72Sha]. No homogeneity range is known. The form of the Li2S liquidus on the S-rich side in the assessed diagram is based on [72Sha]. The Li-rich liquidus has not been determined. The S-rich liquid phase shows immiscibility [72Cun, 72Sha]. The form of the miscibility gap in the assessed diagram is adopted from [72Sha], with the critical point at about 91 at.% S and 860 C. The critical composition is approximate, due to sparse data points near the critical point. The S-rich side of the miscibility gap measured by [72Cun] and [72Sha] is reasonably consistent. The reason for the discrepancy of ~5 at.% in the miscibility gap measurements by [72Cun] and [72Sha] on the Li-rich side is unknown. The accepted monotectic composition is 65.5 at.% S [72Sha], and the monotectic temperature is shown at 365 C in the assessed diagram, which is close to 364. 8 C given by [72Cun] and within the limit of 362 с 3 C given by [72Sha]. The melting point of bS and the bS = aS allotropic transformation temperature are 115.22 [Melt] and ~95.5 C, respectively. The L to (bS) transformation in alloys may be eutectic, because the transformation temperature (115.5 C) is lower than the observed melting point of bS (118.0 C) [72Cun]. The actual transformation temperature must be very close to the melting point of pure bS, because the solubility of Li in (bS) is very small. Hence, the transformation is shown at the melting point of bS in the assessed diagram. The type of (bS) to (aS) transformation is unknown. [72Cun] observed it at 104 C. The actual temperature is probably very close to that of the allotropic transformation of pure S because of the presumed small solubility of Li in (aS) . [31Pea] found a stable Li2S2 compound, with a melting point at 369.5 C. However, [72Sha] could not confirm its existence. [31Pea] also reported a less stable Li2S4. These compounds may exist as metastable phases. 31Pea: T.G. Pearson and P.L. Robinson, J. Chem. Soc., 413-420 (1931). 72Cun: P.T. Cunningham, S.A. Johnson, and E.J. Cairns, J. Electrochem. Soc., 119(11), 1448-1450 (1972). 72Sha: R.A. Sharma, J. Electrochem. Soc., 119(11), 1439-1443 (1972). Submitted to the APD Program. Complete evaluation contains 2 figures, 4 tables, and 8 references. 1