ISSN 0036-0244, Russian Journal of Physical Chemistry, 2006, Vol. 80, No. 5, pp. 689–692. © Pleiades Publishing, Inc., 2006.
Original Russian Text © V.A. Titov, E.E. Grinberg, 2006, published in Zhurnal Fizicheskoi Khimii, 2006, Vol. 80, No. 5, pp. 799–802.
CHEMICAL THERMODYNAMICS
AND THERMOCHEMISTRY
The Thermodynamic Characteristics of Sublimation
of Chromium Trichloride
a
b
V. A. Titov and E. E. Grinberg
a
Institute of Inorganic Chemistry, Siberian Division, Russian Academy of Sciences,
pr. Akademika Lavrent’eva 3, Novosibirsk, 630090 Russia
b
Research Institute of Chemical Reagents and Special-Purity Substances, Moscow, Russia
E-mail: tv@che.nsk.ru
Received May 24, 2005
Abstract—The sublimation of stoichiometric chromium trichloride was experimentally studied by the static
method of vapor pressure measurements. The main reaction was found to be CrCl (cr) = CrCl (g). The enthalpy
3
3
and entropy of this reaction were calculated. Sublimation was also performed in the presence of excess chlorine.
The thermodynamic characteristics of the reaction 2CrCl (g) + Cl = 2CrCl (g) were estimated.
3
2
4
DOI: 10.1134/S0036024406050049
INTRODUCTION
tion [4], it is 1097 K; and, according to [15], CrCl2
melts above 1423 K. It follows that heating stoichio-
Chromium trichloride has long and successfully
been used as a reagent in inorganic and organoelement
synthesis and also for the preparation of chromium
coatings. The execution of the corresponding reac-
tions in practice shows that compound purity is of
considerable importance for obtaining acceptable
results. Chromium trichloride does not exist in the liq-
uid state at practicable rectification temperatures, and
the determination of optimum sublimation purifica-
tion conditions requires knowledge of the composi-
tion of its vapor and the temperature dependence of
vapor pressure.
metric CrCl should correspond to monovariant equi-
3
librium and the introduction of additional chlorine into
the system should result in divariant equilibrium, but an
additional material balance equation then appears
because the amount of excess chlorine is known. These
circumstances allow the system to be studied by the
static method of vapor pressure measurements.
EXPERIMENTAL
We used industrial samples prepared and purified by
different methods. Sample 1 was obtained by the chlo-
rination of a mixture of chromium oxide and carbon.
Sample 2 was synthesized in the reaction between chro-
mium oxide and dry carbon tetrachloride taken in large
excess at ~1300 K. The product deposited in the cold
quartz reactor zone was not subjected to additional
purification. Sample 3 was obtained in a similar reac-
tion and subjected to sublimation purification in a flow
of chlorine. Sample 4 was prepared similarly to sam-
ple 2 and purified by the hydrothermal method at 360–
The vaporization of chromium trichloride under
heating has been the object of a huge number of studies
[1–13]. Nevertheless, it is still not completely clear
what the pressure and molecular composition of its
vapor and the phase composition of the substance dur-
ing sublimation are. This is explained by the possibility
of simultaneous occurrence of several processes at
9
00–1500 K, namely,
CrCl (cr) = CrCl ,
(1)
3
3
3
65 K. According to the iodometric titration data, the
2
CrCl (cr) = CrCl (cr) + CrCl or
3 2 4
content of the major component in samples 1–4 was 94,
95, 97, and 96 wt %; the content of high-volatility
hydrocarbons (mainly hexachlorobenzene) was 1.5, 3,
(2)
2
CrCl (cr) = CrCl (sln) + CrCl ,
3
2
4
0
.5, and 1.2 wt %; and the content of low-volatility
CrCl = CrCl + Cl ,
(3)
(4)
4
2
2
compounds was 3.5, 3, 2.5, and <2 wt %, respectively.
According to the atomic emission analysis data, the
contents of the other elements in all samples were: Ni,
2
CrCl + Cl = 2CrCl .
3 2 4
According to experimental studies, the melting 0.15–0.19 wt %; iron, 0.02–0.09 wt %; and silicon,
point of chromium dichloride lies within the interval 0.01–0.02 wt %. The concentrations of Ag, Be, Mn, In,
t (CrCl (cr)) = 1069–1096°C; according to the data of Cd, Ga, Cu, Co, Bi, Pb, Tl, Mo, Au, Ge, Sn, Ti, Al, Mg,
m
2
the Termotsentr (Thermocenter) of the Russian Federa- Zn, Pt, Ba, As, and Te were below the detection limit.
6
89