Фазовая диаграмма системы Cd-O

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Cd-O (Cadmium-Oxygen) H.A. Wriedt The equilibrium solid phases of the condensed Cd-O system at 0.1 MPa hydrostatic pressure are (1) the cph terminal solid solution, (Cd), with a very narrow composition range; (2) the fcc oxide, CdO, with a narrow but significant composition range; and (3) the cubic peroxide, CdO2, with an unknown composition range. No published phase diagram for the Cd-O system was found in the literature. A required (Cd) + L + CdO three-phase equilibrium of the condensed system has not been observed but is listed here with other known transformations. The melting point of CdO is unknown. CdO2 has been omitted here because the nature and temperature of its transformation(s) are unknown. No polymorphic changes are known for any of the phases at 0.1 MPa hydrostatic pressure. Because the only data for phase boundaries are fragmentary and limited to the Cd-rich liquidus of CdO (liquid Cd compositions) and the corresponding solidus, the phase diagram has few details. (Cd) is stable only at low fugacities of O2. In the condensed system, O- saturated (Cd) is in equilibrium with CdO. The (Cd) solvus has not been determined. Although no data are available, on the basis of the minute solubility of O determined for liquid Cd, it is concluded that the (Cd) field is very narrow. The (Cd) solidus and liquidus are also undetermined. CdO exhibits no solid-state transformations. The only attempt to determine the melting point was unsuccessful because the specimen sublimed above 1500 C without melting [61Rot]. At its Cd-rich limit, CdO is in equilibrium with (Cd) or liquid Cd. Although the equilibrium has not been realized, it appears that CdO would be in equilibrium with CdO2 or liquid at its O-rich limit, if sufficiently high O2 fugacities were imposed. The range of compositions of CdO is fairly narrow, but the variation is technically important because of the large change in electrical conductivity that attends the change in the O content [33Bau]. Very little research has been directed at determining the boundary compositions; the upper boundaries are completely unknown. No experiments with O2 fugacities exceeding about 0.1 MPa have been reported, although the upper boundary is at higher fugacities. No specimen of CdO has been shown by chemical (or other) analysis to contain more than the stoichiometric proportion of O2, but at least a very slight excess of Cd was present in all specimens observed, even those prepared in O2. In no instance has CdO2 been equilibrated with another Cd oxide or gaseous O2. Nevertheless, it has been included here as an equilibrium phase of the Cd-O system because it is the highest oxide of which the existence is established. If sufficiently high O2 fugacities could be imposed, it is probable that O- rich CdO would coexist in equilibrium with Cd-rich CdO2. Although the existence of CdO2 is widely acknowledged, it probably has not been produced in the pure state [62Van]. The limits of deviation in composition from stoichiometric CdO2 are unknown. [ 62Van] indicated that appreciable amounts of superoxide ion can be incorporated in CdO2, so that the O-rich limit may lie above the stoichiometric composition. CdO is the only condensed phase other than Cd, solid or liquid, for which vaporization has been investigated. Early investigators thought that vapor formed in the congruent vaporization of CdO was composed of CdO molecules, but [51Bre] showed that it was composed almost entirely of monatomic Cd(g) and O2 molecules. [80Gra] reported that experiments had detected less than 0.1 % CdO in the equilibrium vapor over CdO at all temperatures up to 1056 C. [81Beh] indicated that the molecular ratio CdO/Cd in the vapor increased with increasing temperature. [84Kaz] reported that CdO was 0.004% of the equilibrium vapor at 1027 C. Several oxides other than CdO and CdO2 were reportedly prepared. Some of these were not identified with specific stoichiometric compositions, such as the oxide found on molten Cd by [50Gru]. They thought that it was possibly a lower oxide than CdO. Other "suboxides" that were identified with specific compositions were Cd4O, Cd2O, and Cd3O2 [62Chi]. No other report of Cd3O2 has been found. [26Fer] obtained a substance by decomposing Cd oxalate that had previously been identified with Cd4O, but his specimen produced no lines in XRD. Several different oxides that were called "peroxides" other than CdO2 may exist. Often the given compositions are accompanied by a qualification that they occur hydrated or in combination with Cd hydroxide or H2O2. The latter compounds are omitted here as nonbinary, but the reported compositions of hydrated oxides are given because of the implication that they may exist in the anhydrous state. In review, [62Chi] lists these so-called "peroxides" as Cd2O3, Cd5O8, Cd3O5, and Cd4O7. The "peroxides" were said by [62Chi] to have formed when Cd hydroxide or a Cd salt was treated with H2O2 or CdO with O3 or even air. Cadmium superoxide, CdO4, has not been prepared as a discrete phase [62Van]. [ 62Van], however, indicated that 13% superoxide developed in "Cd peroxide" treated with moist air at 100 C. Reaction of Cd(NO3)2 with NaO2 (sodium superoxide) in liquid NH3 yielded CdO2, not CdO4 [54Sch]. Molecules of CdO3 in solid N2 or Ar were detected by spectroscopic analysis of products of the " matrix" reaction of vaporized Cd with O3 which had been mixed with N2 or Ar [ 80Pro]. 26Fer: A. Ferrari, Gazz. Chim. Ital., 56, 630-637 (1926) in Italian. 33Bau: H.H. von Baumbach and C. Wagner, Z. Phys. Chem. B, 22, 199-211 (1933) in German. 50Gru: W. Gruhl and G. Wassermann, Z. Metallkd., 41, 178-184 (1950) in German. 51Bre: L. Brewer and D.F. Mastick, J. Chem. Phys., 19(7), 834-843 (1951). 54Sch: D.L. Schechter and J. Kleinberg, J. Am. Chem. Soc., 76, 3297-3300 (1954) . 61Rot: R.S. Roth, J. Am. Ceram. Soc., 44(1), 49-50 (1961). 62Chi: D.M. Chizhikov, Cadmium, Izv. Akad. Nauk SSSR, Moscow (1962) in Russian; TR: Pergamon, New York (1966). 62Van: N.-G. Vannerberg, Prog. Inorg. Chem., 4, 125-197 (1962). 66Per: E.A. Perez-Albuerne, R.L. Clendenen, R.W. Lynch, and H.G. Drickamer, Phys. Rev. (Ser. 2), 392-399 (1966). 79Kje: A. Kjekshus and T. Rakke, Acta Chem. Scand., A, 33, 617-620 (1979). 80Gra: M. Grade and W. Hirschwald, Z. Anorg. Allg. Chem., 460, 106-114 (1980). 80Pro: E.S. Prochaska and L. Andrews, J. Chem. Phys., 72(12), 6782-6793 (1980). 81Beh: R.G. Behrens and C.F.V. Mason, J. Less-Common Met., 77, 169-184 (1981). 84Kaz: E.K. Kazenas, G.N. Zviadadze, and M.A. Bol'shikh, Izv. Akad. Nauk SSSR, Met., (2), 67-70 (1984) in Russian; TR: Russ. Metall., (2), 58-61 (1984). Published in Bull. Alloy Phase Diagrams, 8(2), Apr 1987. Complete evaluation contains 1 figure, 8 tables, and 85 references. Special Points of the Cd-O System