Фазовая диаграмма системы Cd-O
К оглавлению: Другие диаграммы (Others phase diargams)
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