Russian Journal of Applied Chemistry, 2010, Vol. 83, No. 1, pp. 65−71.
Pleiades Publishing, Ltd., 2010.
Original Russian Text
V.I. Balakai, A.V. Arzumanova, K.V. Balakai, 2010, published in Zhurnal Prikladnoi Khimii, 2010, Vol. 83, No. 1, pp. 67−74.
AND CORROSION PROTECTION OF METALS
Alkalization of the Near-Cathode Layer in Electrodeposition
of Nickel from a Chloride Electrode
V. I. Balakai, A. V. Arzumanova, and K. V. Balakai
South-Russian State Technical University, Novocherkassk, Rostov-on-Don oblast, Russia
Received April 15, 2009
Abstract—Dependences of the pH at which hydrate formation begins and the pH of the near-cathode layer on
the electrolysis modes (temperature, cathode current density, pH in the electrolyte bulk) and the dependence of
the pH of the near-cathode layer on the distance from the cathode surface in a low-concentration chloride nickel-
plating electrolyte were studied.
The electrochemical deposition of metals is frequently
accompanied by simultaneous evolution of hydrogen,
which leads to alkalization of the near-cathode space
and creates conditions in which highly dispersed
sols of hydroxides and basic salts of a metal being
electrodeposited can be formed. Changes in the pH
of the near-cathode layer, pH
, affect the mechanism
and kinetics of electrode reactions and the quality and
structure of the deposit formed.
The formation of colloidal and microheterogeneous
particles in electrolytes in deposition of metals and alloys
and their effect on the properties of the electroplated
coatings obtained and on the metal deposition mechanism
have long attracted the attention of electrochemists.
The fundamental aspects of colloid formation in
cathodic processes of metal discharge have been analyzed
[1–20]. M.N. Polukarov suggested that colloidal and
microheterogeneous compounds of a metal being
electrodeposited are formed near the cathode in the course
of electrolysis. The formation of a metallic coating on the
cathode from particles moving toward its surface has been
observed in those cases when kinetically stable dispersed
systems appear under the electrolysis conditions [2–4].
Electron-microscopic studies have shown that a difﬁ cultly
soluble hydroxide of a metal being electrodeposited
is present on the surface of lustrous deposits [5, 6].
The process of formation of stable colloidal and
microheterogeneous compounds of nickel in the near-
cathode space of various nickel-plating electrolytes has
been studied with an ultramicroscope [7–9]. The authors
of [10–13] examined the formation and stability of colloid
compounds of nickel in nickel-plating electrolytes.
Studies of the Watts nickel-plating electrolyte with
various additives have led to a conclusion that the
dispersity of colloidal particles of basic nickel compounds
affects the quality of the deposits obtained [14–17]. It
was found that the quality of the deposits improved as
the dispersity of colloid nickel compounds increased. In
addition, it was suggested that the electrodeposited nickel
is formed by two simultaneously occurring processes:
discharge of nickel ions and reduction of a ﬁ lm of nickel
hydroxide to the metal by atomic hydrogen formed as
a result of alkalization of the near-cathode space.
V.A. Kaikaris experimentally demonstrated that
colloidal compounds of metals can be reduced at the
cathode to give a compact plated coating. It was found
that, if colloidal particles of compounds of metals being
electrodeposited are present and the conditions of the
two-factor theory of luster formation are satisﬁ ed, a strong
luster of the coatings is obtained [18, 19].
According to the two-factor theory of luster formation,
the following conditions should be satisﬁ ed for lustrous
coatings to be obtained: (1) colloidal particles that can
be reduced by hydrogen or electrons from the cathode
should be formed in the near-cathode layer and (2) forces
aligning the reducing colloidal particles in accordance
with the shape of the fluid 1–fluid 2 phase surface
should be created. In this case, ﬂ uid 1 is the bulk of the