ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2018, Vol. 92, No. 1, pp. 53–56. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © Yu.V. Polenov, E.V. Egorova, G.A. Shestakov, 2018, published in Zhurnal Fizicheskoi Khimii, 2018, Vol. 92, No. 1, pp. 62–65.
CHEMICAL KINETICS
AND CATALYSIS
Kinetics of the Reduction of Cadmium Sulfate
by Thiourea Dioxide in an Aqueous Ammonia Solution
upon the Metallization of Carbon Fiber
Yu. V. Polenov*, E. V. Egorova, and G. A. Shestakov
Ivanovo State University of Chemistry and Technology, Ivanovo, 153000 Russia
*
е-mail: polyurij@yandex.ru
Received March 25, 2017
Abstract—The kinetics of the decomposition of thiourea dioxide and the reduction of cadmium cations by
thiourea dioxide in an aqueous ammonia solution are studied. The kinetic parameters of these reactions are
calculated using experimental data, allowing us to adjust conditions for the synthesis of cadmium coatings on
carbon fiber of grade UKN-M-12K. The presence of the metal crystalline phase on the fiber is confirmed by
means of X-ray diffraction, and its amount is measured via atomic absorption spectroscopy.
Keywords: thiourea dioxide, cadmium, carbon fiber, kinetic model, chemical metallization
DOI: 10.1134/S0036024418010181
INTRODUCTION
mechanism of the reductive action of the latter under
conditions of the metallization of carbon fiber (CF).
The reduction of salts of metals from solutions by
chemical reducing agents is one way of preparing dis-
persions of metals and metal coatings on dielectric
materials. Such compounds as hypophosphite,
sodium borohydride, sodium dithionite, and ron-
galite, which allow us to reduce cations of copper, sil-
ver, palladium, nickel [1–4], and other metals whose
redox potentials are more positive than those of the
reducing agents are traditionally used for these pur-
poses. However, the reduction of cadmium cations,
the redox potential of which in an aqueous medium is
We initially studied the kinetics of the decomposi-
tion of thiourea dioxide in an aqueous ammonia solu-
tion to obtain a kinetic description of the reduction of
cadmium cations. The conditions for applying cad-
mium coatings onto carbon fiber were selected on the
basis of the resulting kinetic data.
EXPERIMENTAL
Solid thiourea dioxide (NH ) CSO , synthesized
2
2
2
from analytical purity grade thiourea and superior
grade mark B hydrogen peroxide according to the pro-
cedure in [11], was used in the present work. The con-
tent of the main substance in the final product, deter-
mined by means of iodometric titration [11], was no
less than 96%.
−0.4, cannot be accomplished with any of the above
reagents.
Thiourea dioxide (TUDO) in an aqueous solution
of ammonia at a concentration of 3 mol/L was used in
[
5] to synthesize a powder of high-purity metallic cad-
In our experimental studies of the kinetics of the
decomposition of TUDO in an aqueous ammonia
solution, the reaction mixture was sampled at regular
time intervals and analyzed to determine the content
of thiourea dioxide via iodometric titration [11].
mium. As is well known, the ammonia complex of
cadmium has a redox potential of −0.66 V [6]; i.e., the
reduction of its ions is more difficult than that of neat
2+
Cd ions. However, the increase in the activity of
TUDO due to the formation of products of its decom-
position (anions of sulfoxylic acid) in this case plays a
For our experimental studies of the kinetics of the
key role [7]. As was shown in [8–10], the reduction of reduction of cadmium sulfate, aqueous solutions of
nickel and palladium ions by thiourea dioxide in an TUDO and cadmium sulfate (chemically pure grade
aqueous ammonia solution also proceeds because of 3CdSO · 8H O was used) were prepared and held for
4 2
2
−
5 min in a thermostat. The solutions were then mixed,
and an ammonia solution was added to the mixture.
the presence of SO2 anions.
The aim of this work was to determine the kinetic
The reaction mixture was sampled at specific time
parameters of the reduction of cadmium cations by intervals, and the concentration of cadmium ions was
thiourea dioxide and identify the stoichiometric analyzed by means of complexometric titration [12].
53