Russian Journal of Applied Chemistry, 2009, Vol. 82, No. 2, pp. 255−261.
Pleiades Publishing, Ltd., 2009.
Original Russian Text
V.I. Balakai, N.Yu. Kurnakova, A.V. Arzumanova, K.V. Balakai, I.V. Balakai, 2009, published in Zhurnal Prikladnoi Khimii,
2009, Vol. 82, No. 2, pp. 262−267.
AND CORROSION PROTECTION OF METALS
Possibility of Raising the Deposition Rate of Nickel Coatings
from a Chloride Electrolyte
V. I. Balakai, N. Yu. Kurnakova, A. V. Arzumanova, K. V. Balakai, and I. V. Balakai
South-Russian State Technical University, Novocherkassk, Rostov-on-Don oblast, Russia
Received February 28, 2008
Abstract—Conditions under which nickel coatings can be deposited from a chloride electrolyte at a high rate
were studied. The mechanism of this process was suggested and experimentally confirmed. The mass-transfer
rate of nickel-containing particles was determined by chronopotentiometry, with temperature raised from 20 to
50°C. The dependence of pH
on the current density was determined. Physicochemical parameters of the coatings
(microhardness, internal stresses, porosity, luster, and adhesion) were measured.
As known [1−3] that it is possible to accelerate
electrodeposi-tion of metal coatings from electrolytes in
which the discharge process involves, together with ions
of electrodeposited metals, also ﬁ nely dispersed particles
of their compounds, capable of discharging to the metal
in the same range of potentials as the ions themselves. In
the course of nickel plating, a kinetically stable system of
ﬁ nely dispersed particles may appear in the near-cathode
space and can intensify the electrodeposition process.
In the optimal case, this system can be likened to a
mobile system of pores, in which arise, in the course of
electrolysis, electrosurface phenomena that cause stirring
of the difﬁ cultly stirrable part of the diffusion layer.
This system should not be necessarily thermally stable.
It is sufﬁ cient that it should be kinetically stable during
electrolysis and possess certain optimal parameters that
enable the appearance of nonequilibrium electrosurface
phenomena. The ﬁ nely dispersed particles generated in
the course of electrolysis may be composed of hydroxide
and basic salt species.
To be discharged at the cathode, the ﬁ nely dispersed
particles should be positively charged. The charge can
be imparted to them via adsorption of nickel cations,
because it is known that inorganic ions contained in
the particle core are primarily adsorbed on dispersed
particles. As the cathode current density increases, the
alkalization of the near-cathode space should become
more pronounced because hydrogen evolution commonly
occurs together with nickel deposition at the cathode. In
high-performance electrolytes, it is necessary to lower
the pH in the solution bulk or choose more effective
buffering additives lest the pH value of the near-cathode
, be shifted too strongly toward the onset pH
of hydrate formation for nickel, pH
, thereby leading to
rapid coagulation and formation of coarsely dispersed
particles and their coagulation and, consequently, to their
Nickel chloride was chosen as the main component
for developing a high-performance electrolyte. Chloride
electrolytes offer wide opportunities for acceleration
of the nickel plating process, because the electrolyte
should not contain large amounts of multiply charged
ions, including sulfate ions, which exhibit coagulating
capacity with respect to sols. In addition, according to
, hydroxide species precipitated upon alkalization
of the solution are positively charged if the starting salt
is a chloride. If, however, the starting salt is a metal
sulfate, negatively charged hydroxide species are formed,
which is undesirable as regards the intensiﬁ cation of the
nickel-plating process. The stability of ﬁ nely dispersed
hydroxide and basic salt particles in the near-cathode
layer in the presence of nickel chloride and their positive
charge can intensify the electrolysis process.
A promising way to make progress in electroplating
is to devise and use high-performance electrolytes con-
taining ﬁ nely dispersed compounds of a metal being
electrodeposited, which are reduced at the cathode [1, 2].
However, the mechanism by which the electrodeposition