Фазовая диаграмма системы Ca-Cu

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Ca-Cu (Calcium-Copper) D.J. Chakrabarti and D.E. Laughlin The equilibrium phases of the Cu-Ca system are (1) the liquid, miscible in all proportions and stable down to 482 C at 75.7 at.% Ca; (2) the fcc solid solution, (Cu), with limited solubility of Ca; (3) the bcc solid solution, ( bCa), with negligible solubility of Cu and stable down to ~443 C; (4) the fcc solid solution, (aCa), with negligible solubility of Cu and stable below ~443 C; (5) the hexagonal phase Cu5Ca, with a composition that includes the stoichiometric composition, stable below 950 C; (6) the orthorhombic stoichiometric phase bCuCa, stable between 567 C and some undefined lower temperature; (7) the monoclinic low-temperature modification of the CuCa phase, aCuCa, whose temperature limits of stability have not been defined; and (8) the orthorhombic stoichiometric phase CuCa2, which forms peritectically at 488 C. The assessed Cu-Ca phase diagram has been derived primarily from the work of [ 71Bru]. The liquidus is characterized by four temperature-invariant transformations, corresponding to two eutectic and two peritectic reactions. Three intermediate phases of stoichiometry Cu5Ca, CuCa, and CuCa2 are present, with Cu5Ca having a limited solubility field and undergoing congruent melting at 950 C. The crystal structures of the intermediate phases constitute prototypes of new structures. Ca is very reactive in air, and the Cu-Ca alloys behave similarly. Thus, contamination is a problem with these alloys, particularly in the liquid. Because the Cu-Ca phase diagram is reasonably well established, the equilibrium boundaries between the coexisting phases can be used to derive expressions for the thermodynamic variables of the different phases. 71Bru: G. Bruzzone, J. Less-Common Met., 25, 361-366 (1971). Published in Bull. Alloy Phase Diagrams, 5(6), Dec 1984. Complete evaluation contains 2 figures, 6 tables, and 23 references. Special Points of the Cu-Ca System