VAPOR PRESSURE OVER KI–CoI2 MELTS
205
Table 4. Equilibrium composition of the vapor phase result- ations from Raoult’s law behavior, in accordance with
ing from CoI2 vaporization and decomposition
our results (Fig. 3).
Thermal-emf measurements in the range 798–913 K
[15] also revealed appreciable negative deviations from
ideality at mole fractions of CoI2 from 0.3 to 0.9, which
lends further support to the present results.
T, K
1020
1048
1062
1080
pCoI , Pa
6346
1136
2784
9967
1619
3481
15439
2141
4821
22745
2806
6186
2
pI, Pa
CONCLUSIONS
pI , Pa
2
The vaporization of KI–CoI2 melts was studied in a
wide pressure range.
over pure CoI2 are I, I2, and, probably, Co2I4. Since
studies of cobalt halide dimerization [7–9] did not
reveal significant amounts of Co2I4, this dimer will be
left out of consideration in what follows.
To find the vapor composition over CoI2, we use the
following equations:
Calculations of vapor pressure isotherms in the KI–
CoI2 system revealed negative deviations from linear-
ity. The vapor composition over pure CoI2 was deter-
mined, and the temperature-dependent vapor pressure
of CoI2 was evaluated. The boiling point of pure CoI2
was found to be 1160 K.
ëÓ(s) + 2I(g) = ëÓI2 (g),
(3)
REFERENCES
K1 = pCoI /p21,
(4)
(5)
2
1. Novoselova, A.V., Rare Metals and Their Applications,
in Seriya XI: Khimiya (Series XI: Chemistry), Moscow:
Znanie, 1966, no. 4, p. 24.
I2(g) = 2I(g),
2. Schafer, H., Chemical Transport as a Preparative
Method, Preparative Methods in Solid State Chemistry,
Hagenmuller, P., Ed., NewYork:Academic, 1972. Trans-
lated under the title Preparativnye metody v khimii tver-
dogo tela, Moscow: Mir, 1976, pp. 277–303.
K2 = p2I /p ,
(6)
(7)
I2
pI + pI + pCol = p .
2
2
Bartovska et al. [10] obtained for reaction (3) in the
3. Burylev, B.P., Mironov, V.L., Tsemekhman, L.Sh., and
Sryvalin, I.T., Equilibrium Vapor Pressures over Molten
Salts in CoCl2–MCl Systems, Izv. Vyssh. Uchebn.
Zaved., Khim. Khim. Tekhnol., 1975, vol. 18, no. 4,
pp. 663–665.
range 970–1330 K
logK1 = 4250/T – 2.125 [Pa].
(8)
For reaction (5), Kuniya et al. [11] found
4. Kornilov, N.I., Buryleva, E.B., and Mironov, V.L., Vapor
Pressures and Thermodynamic Properties of the Constit-
uent Bromides in the System CoBr2–KBr, in Fiziko-
khimicheskie issledovaniya metallurgicheskikh prot-
sessov (Physicochemical Investigation of Metallurgical
Processes), Sverdlovsk: Ural. Politekh. Inst., 1981,
pp. 34–38.
logK2 = –7818/T + 0.528logT + 8.742 [Pa]. (9)
The calculated pressures of different vapor species over
CoI2 are listed in Table 4.
From these data, we obtain for the temperature-
dependent equilibrium vapor pressure of CoI2
5. Buryleva, E.B., Mironov, V.L., Garanina, I.A., and
Ignat’eva, L.N., Temperature-Dependent Equilibrium
Vapor Pressures of Rare-Earth Halides and Their Alloys,
Zh. Fiz. Khim., 1976, vol. 50, no. 8, pp. 2174–2175.
log p = –10294/T + 13.872 [Pa].
(10)
6. Veryatin, U.D., Mashirev, V.P., Ryabtsev, N.G., et al., Ter-
modinamicheskie svoistva neorganicheskikh veshchestv:
Spravochnik (Thermodynamic Properties of Inorganic
Substances: A Handbook), Zefirov, A.P., Ed., Moscow:
Atomizdat, 1965, p. 460.
The boiling point is, therefore, 1160 K, which far
exceeds the 1033 K indicated in [12], in accordance
with earlier findings [13].
The present results are in satisfactory agreement
with the data obtained by Hill et al. [8] using Knudsen-
cell vaporization measurements in the range 537–664 K
and by the torsion method in the range 616–678 K, in
spite of the difference between the temperature ranges
studied.
7. Schoonmaker, R.C., Friedman, A.H., and Porter, R.F.,
Mass Spectrometric and Thermodynamic Study of Gas-
eous Transition Metal(II) Halides, J. Chem. Phys., 1959,
vol. 31, no. 6, pp. 1586–1589.
8. Hill, S.D., Clealand, C.A., Adams, A., et al., Vapor Pres-
sures and Heats of Sublimation of Cobalt Dihalides,
J. Chem. Eng. Data, 1969, vol. 14, pp. 84–89.
The structure of the KI–CoI2 phase diagram [14]
(the existence of K2CoI4) points to large negative devi-
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