Russian Journal of Applied Chemistry, 2010, Vol. 83, No. 11, pp. 1944−1947.
Pleiades Publishing, Ltd., 2010.
Original Russian Text © A.V. Novoselova, V.V. Smolenskii, 2010, published in Zhurnal Prikladnoi Khimii, 2010, Vol. 83, No. 11, pp. 1812−1815.
AND CORROSION PROTECTION OF METALS
Electrochemical and Thermodynamic Properties
of Thulium Trichloride in a Molten NaCl–KCl–CsCl Eutectic
A. V. Novoselova and V. V. Smolenskii
Institute of High-Temperature Electrochemistry, Ural Branch, Russian Academy of Sciences, Yekaterinburg, Russia
Received July 6, 2010
Abstract—Potentiometric method was used to measure the redox potentials of Tm
in a eutectic melt of
sodium, potassium, and cesium chlorides relative to a chlorine reference electrode in the temperature range 823–
973 K. The main thermodynamic characteristics of the redox reaction TmCl
were calculate from the conditional standard potentials E
Lanthanides (Ln) are present in high-activity waste
as ﬁ ssion products. In addition, they are neutron poisons
and, therefore, should be separated from the main
components (U, Pu) in processing of spent nuclear fuel.
Moreover, the chemical and electrochemical properties
of lanthanides and actinides (An) are very close [1–
6], and, therefore, their separation is difﬁ cult. For the
same reason, it is highly important to know the redox
potentials of An and Ln in molten media.
There is only scarce published evidence about
the redox potentials of thulium [7–9]. In , the
electroreduction of Tm
ions on W and Mo electrodes
in a NaCl–KCl melt was studied by cyclic voltammetry
and the diffusion coefﬁ cients of Tm
calculated. The electrochemical behavior of Tm(III) ions
in a low-melting eutectic melt 3LiCl–2KCl on W and Al
electrodes was studied in  in the temperature range
673–823 K. The diffusion coefﬁ cients of Tm(III) and
Tm(II) ions were found, the solubilities of TmOCl and
were calculated, and it was shown that Al–Tm
alloys are formed. The redox potentials of Tm
a CsCl melt were measured in  and their temperature
dependence was presented. A deeper and more detailed
analysis of the occurring processes is impossible without
a systematic study by means of precision methods
directly yielding the necessary information.
Electrochemical techniques are the most widely
used, reliable, and informative methods for study of
the thermodynamic properties of molten systems.
One of ways to ﬁ nd the thermodynamic parameters of
chemical reactions is based on measurements of the
electromotive force of galvanic cells. Electromotive
force measurements in salt melts, which can be regarded
as equilibrium measurements with high reliability,
enable analysis of the thermodynamic properties of
substances at elevated temperatures without additional
In this study, we measured the electromotive force of
the following galvanic cell
in a low-melting nonhygroscopic eutectic mixture of
sodium, potassium, and cesium chlorides in relation
to the ratio between the thulium tri- and dichloride
concentrations at various temperatures.
We used sodium, potassium, and cesium chlorides
of special-purity, analytically pure, and chemically pure
grades, respectively. Preliminarily, these compounds
were subjected to prolonged drying in a vacuum under
conditions of gradually increasing temperature, melted
in the atmosphere of an inert gas, puriﬁ ed by the zone