The Cs-Sn (Cesium-Tin) System
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The Cs-Sn (Cesium-Tin) System J. Sangster* and C.W. Bale École Polytechnique de Montréal
Equilibrium Diagram
analysis revealed only Cs and CsSn. The absence of Cs-rich compounds was corroborated by [79Str].
The assessed Cs-Sn phase diagram is shown in Fig. 1, and the special points of this diagram are listed in Table 1.
CsSn was prepared by direct reaction between the elements [64Hew, 79Dri, 79Str, 81Dri, 82Yat, 87Mel] and was characterized by its x-ray powder diffraction pattern [64Hew, 87Mel]. According to [79Dri, 81Dri], this compound melts incongruently at 630 °C, showing a peritectic composition of 41 at.% Sn. Later work [82Yat, 87Mel], claims that CsSn melts congruently at 884 °C, with a solid transition at 630 °C. In the proposed phase diagram [82Yat, 87Mel] however, the presence of a congruently melting CsSn implies the presence also of a high-temperature eutectic. The published diagram [87Mel] shows thermal arrests that may correspond to this eutectic, but there is no mention of this in the text. Further, although the Li-Sn and Na-Sn systems both contain congruently melting one-to-one compounds, the corresponding compounds in both the K-Sn and Rb-Sn systems melt incongruently. The assessed Cs-Sn phase diagram shows a peritectic for CsSn in conformity with the other heavy alkali metal + Sn systems.
The assessed phase diagram was constructed from the combined results of two independent studies [79Dri, 81Dri] and [82Yat, 87Mel]. The liquidus data in both studies were given only as points on phase diagrams, from which they were read. Both groups performed thermal analyses on alloys in sealed containers, either of stainless steel [79Dri, 81Dri] or Mo [82Yat, 87Mel]. In the more recent work [82Yat, 87Mel], the boundary of the two-liquid phase region was defined through “thermomagnetic analysis” and “solubility” measurements. There are two eutectics in this system, the temperatures of both of which are indistinguishable from the melting points of the pure elements. The eutectic compositions were assumed to be almost identical to the pure components (a liquid alloy of 99.5 at.% Sn showed a thermal arrest at the eutectic temperature, ~28 ° C), and zero solid solubility [87Mel] was implied. In the absence of any more specific information, these assumptions are incorporated in Fig. 1.
Cs2Sn3 was prepared by direct reaction of the elements [79Dri, 81Dri, 82Yat, 84Dri, 87Mel]. It melts congruently, and its melting point is the highest temperature on the Cs-Sn liquidus: 930 °C [79Dri, 81Dri] or 935 °C [82Yat, 87Mel]. The compound was characterized by its powder x-ray [79Dri, 84Dri] and neutron [84Dri] diffraction patterns.
The monotectic temperature was reported to be 605 °C [79Dri, 81Dri] or 590 °C [87Mel, 82Yat]. The miscibility gap at the monotectic temperature is according to [79Dri, 81Dri], 7.5 to 39 at.% Sn as stated in the text. However, on their phase diagrams [79Dri, 81Dri] the range is 10 to 39 at.% Sn. The boundaries of the two-phase liquid region were better defined by [82Yat, 87Mel] to be 2.3 to 39 a
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