Фазовая диаграмма системы K-Zn

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K-Zn (Potassium-Zinc) A.D. Pelton The assessed phase diagram for the K-Zn system is based on the data of [08Smi]. It exhibits a very wide range of liquid immiscibility with one compound, KZn13, which melts (syntectically) to form two immiscible liquids at 592 с 5 C. The two eutectics are essentially coincident with the melting points of the pure elements. The phase diagram very closely resembles the Na-Zn phase diagram, except that the region of immiscibility is wider, as expected. Thermal arrests were observed by [08Smi] at 2 at.% Zn and at 98 at.% Zn, so the miscibility gap is at least this wide. In the Na-Zn system, the gap extends at 557 C from 0.8 to 93.5 at.% Zn. That is, Na is more soluble in Zn than Zn is in Na. This may also be true of the K-Zn system. As a very rough estimate, the gap in the K-Zn system at 592 C probably extends from around 0.2 to about 99 at.% Zn. [08Smi] originally proposed the formula KZn12 for the compound KZn13, but X- ray work [37Ket, 37Zin, 38Zin, 52Sho] has shown conclusively that the formula is KZn13, isotypic with NaZn13, RbZn13, KCd13, RbCd13, and CsCd13. This formula has also been confirmed by chemical analysis [38Zin]. No other compounds have been reported. Some unusual arrests in the cooling curves were reported by [08Smi] over the range 60 to 91 at.% Zn in the temperature range 439 to 571 C. Although [08Smi] suggested that these might be indicative of an allotropic transformation of KZn13, this seems very unlikely. Nonequilibrium effects would be expected in thermal analysis experiments when a solid is formed from two immiscible liquids. Most likely the invariant reaction was not complete at 592 C. 08Smi: D.P. Smith, Z. Anorg. Allg. Chem., 56, 114-119 (1908) in German. 37Ket: J.A.A. Ketelaar, J. Chem. Phys., 5, 668 (1937). 37Zin: E. Zintl and W. Haucke, Naturwissenschaften, 25, 717 (1937) in German. 38Zin: E. Zintl and W. Haucke, Z. Elektrochem., 44, 104-111 (1938) in German. 52Sho: D.P. Shoemaker, R.E. Marsh, F.J. Ewing, and L. Pauling, Acta Crystallogr. 5, 637-644 (1952). Published in Bull. Alloy Phase Diagrams, 8(6), Dec 1987. Complete evaluation contains 1 figure, 2 tables, and 6 references. Special Points of the K-Zn System