Фазовая диаграмма системы Cd-Na

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Cd-Na (Cadmium-Sodium) A.D. Pelton The assessed phase diagram for the Cd-Na system is based primarily on the thermal analysis measurements of [06Mat] and [07Kur] and the sampling and analysis measurements of [64Wee]. The assessed diagram was calculated from thermodynamic analysis. The thermodynamic properties of this system were measured several times, and the phase diagram and the thermodynamic data are in excellent agreement. The compound Cd11Na2 has now been identified as such by crystal structure determinations. Previously, this compound was thought to be Cd5Na or Cd6Na. The compound Cd2Na has an extremely complex cubic crystal structure that corresponds to the composition Cd1.92Na. Both Cd11Na and Cd2Na may exhibit narrow ranges of inhomogeneity. Cd2Na has a congruent melting point of 385 C. Freezing point depressions of Cd caused by Na additions of 1.3 at.% or less have been measured by [07Kur]. The observations agree well with the limiting freezing point depression for no solid solubility calculated thermodynamically with the enthalpy of fusion of Cd given by [83Cha]. Measurements of Na activity in the liquid phase in the composition range near pure Cd indicate quite strong negative deviations from ideality. Furthermore, the activity coefficient of Na does not approach a constant value even in extremely dilute solutions. It is thus clear that the activity coefficient of Cd in the liquid decreases quite rapidly with small Na additions. For this reason, the calculated Cd liquidus drops quickly at Na contents above 2 at.%. Liquidus points reported by [07Kur] at 3.5 and 4.7 at.% Na lie several degrees above the calculated liquidus. However, it is not possible for the liquidus to pass through these experimental points and then drop very rapidly to the eutectic reported by these authors (5.5 at.% Na at 291 C), which is close to the calculated eutectic. The assumption of some solid solubility of Na in (Cd) could improve the agreement between the calculated and reported Cd liquidus. However, based on the difference in atomic radii of Na and Cd, any significant solid solubility is unlikely. Eutectic halts were observed by [07Kur] at the lowest Na content reported of 1.17 at.%. 06Mat: C.H. Mathewson, Z. Anorg. Allg. Chem., 50, 180-187 (1906). 07Kur: N.S. Kurnakow and A.N. Kusnetzow, Z. Anorg. Allg. Chem., 52, 173-185 ( 1907). 62Sam: S. Samson, Nature, 195, 259-262 (1962). 64Wee: J.R. Weeks and H.A. Davies, AEC Rep., Conf. 660712-1, BNL-10372, 23 p ( 1964). 83Cha: M.W. Chase, Bull. Alloy Phase Diagrams, 4(1), 124 (1983). Published in Bull. Alloy Phase Diagrams, 9(1), Feb 1988. Complete evaluation contains 3 figures, 1 table, and 30 references. 1