Study of properties of lustrous nickel coatings deposited from a low-concentration chloride electrolyte

Article abstract of DOI:10.1134/S1070427211100107

Effect of electrolysis modes on the physicomechanical properties of lustrous nickel coatings deposited from a low-concentration chloride electrolyte was examined. Results obtained in an experimental study of the industrial use of the given electrolyte are presented.

Full text of DOI:10.1134/S1070427211100107

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2011, Vol. 84, No. 10, pp. 1732−1737. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © V.I. Balakai, N.Yu. Kurnakova, K.V. Murzenko, I.F. Byrylov, D.N. Kuznetsov, 2011, published in Zhurnal Prikladnoi Khimii, 2011,
Vol. 84, No. 10, pp. 1640−1645.
APPLIED ELECTROCHEMISTRY
AND CORROSION PROTECTION OF METALS
Study of Properties of Lustrous Nickel Coatings Deposited
from a Low-Concentration Chloride Electrolyte
V. I. Balakai, N. Yu. Kurnakova, K. V. Murzenko, I. F. Byrylov,
and D. N. Kuznetsov
South-Russian State Technical University (Novocherkassk Polytechnic Institute, Novocherkassk,
Rostov-on-Don oblast, Russia
Received May 12, 2010
Abstract—Effect of electrolysis modes on the physicomechanical properties of lustrous nickel coatings deposited
from a low-concentration chloride electrolyte was examined. Results obtained in an experimental study of the
industrial use of the given electrolyte are presented.
DOI: 10.1134/S1070427211100107
Use of dilute electrolytes meets requirements of
environment protection because this can diminish
the content of heavy metal ions in wastewater and
atmosphere and even enable development of low-waste
and waste-free technologies. A considerable economical
effect can be achieved owing to a decrease in the reagent
consumption for preparation and adjustment of the
electrolyte and lower expenses and energy expenditure
for wastewater purification. In some cases, coatings
with new functional properties can be obtained.
unreduced molecules of nickel compounds, contained in
a dispersed particle, are incorporated into a coating and
thereby lead to changes in coating properties [luster,
internal stress (IS), microhardness, adhesion, corrosion
resistance, uniformity of the deposit distribution over
article surfaces, and porosity].
The goal of our study was to examine properties
of nickel coatings deposited from a low-concentration
chloride electrolyte and the possibility of their use for
deposition of protective-decorative coatings.
Chloride nickel-plating electrolytes are advantageous
over sulfate and sulfate-chloride electrolytes in having
a higher electrical conductivity, causing no anode
passivation, and exhibiting a weaker tendency toward
coagulation of sols [1, 2].
EXPERIMENTAL
We used an electrolyte of composition (electrolyte 1)
–1
(
g l ): NiCl ·6H O 100, NiSO ·7H O 5, H BO 35,
2
2
4
2
3
3
It was shown in [3] that, in the course of electrolysis
in a chloride nickel-plating electrolyte, the near-cathode
layer is alkalized and colloidal and finely dispersed
compounds of the metal being electrodeposited are
formed. It follows from [4] that particles of the hydroxide
being precipitated upon alkalization of the solution bear
a positive charge if a metal chloride is the starting salt,
and a negative charge if this is the metal sulfate.
chloramine B 1.5; still bottoms of 1,4-butynediol (SBB)
5 ml l . The electrolysis mode was the following:
temperature 20–60°C, pH 1.0–5.0, cathode current
density 0.5–12 A dm–2 [5]. Nickel was deposited onto
articles made of St.3 steel, M1 copper, and L63 brass
in a 250-ml cell. The sample surface was pretreated by
the known methods [6]. NPA-1 nickel served as anodes.
The microhardness of coatings with thicknesses of no
less than 25 μm on a copper plate was determined with
PMT-3 microhardness meter at an indenter load of 50 g
in conformity with GOST (State Standard) 2999–75. The
–
1
The stability of colloidal and finely dispersed
compounds and basic salts of nickel in the near-cathode
layer in the presence of nickel chloride may result in that
1
732

STUDY OF PROPERTIES OF LUSTROUS NICKEL COATINGS
1733
internal stresses were found by the method described
determined by the method described in [3].
in [7], with a flexible horizontally arranged cathode.
A 35 × 10 × 0.05 mm copper cathode being tested was
preliminarily annealed at a temperature of 700°C for
One of the most important tasks in the field of elec-
trodeposition of metals is to develop an electrolyte and
conditions in which coatings with prescribed properties
can be deposited. The physicomechanical properties of
electrolytic deposits, important quality characteristics of
coatings, predetermine their application areas.
3
0 min [8] and then was cooled in a closed furnace to
room temperature. The substrates were insulated on one
side with a poly(vinyl chloride) lacquer. Deviations of
the cathode from the original position were recorded
using a MIR-2 microscope. The IS was calculated by
the formula
One of properties characterizing the quality and
corrosion resistance of electroplated coatings is their
porosity. It is known that this property depends on
whether IS appears in deposits and on the quality of the
preliminary treatment of the substrate surface, substrate
material, current efficiency, and electrolysis modes.
Finding reasons for pore formation in deposits is one of
the most important issues in electrolytic deposition of
metals and alloys.
2
Ed z
IS = –––– ,
2
3
δl
where E is the elastic modulus of the substrate material;
d, cathode thickness (m); z, cathode end deflection (m);
δ, coating thickness (m); and l, length of the coated part
of the cathode (m).
It can be seen in Fig. 1a that the porosity of coatings
deposited at a temperature of 20°C, pH 1.0, and coating
–
2
Changes in the luster of the nickel coatings were
studied on 50 × 60 × 0.5 mm steel plates with an FB-
thickness of 6 μm at current densities of 1–5 A dm
–
2
increases from 13 to 15 pores cm and then decreases
to 12 pores cm as the current density is raised
to 9 A dm . It was found that the porosity of 6-μm-
–
2
1
A luster meter. As the reference whose luster was
–
2
taken to be 100% served a polished copper plate coated
with a 20-μm-thick layer of lustrous nickel from the
thick coatings deposited at a cathode current density of
5 A dm and pH 1.0 decreases from 15 to 9 pores cm
–
1
–2
–2
electrolyte of composition (g l ): NiSO ·7H O 260–
4
2
3
00, NiCl 6H O 40–60, H BO 30–40, 1,4-butynediol
as the electrolyte temperature is raised from 20 to 60°C
(Fig. 1b). For coatings deposited at a current density
2
2
3
3
(100%) 0.12–0.2, saccharine 1.5–2.0, and phthalimide
–
2
0
5
3
.08–0.12. The electrolysis was performed at pH 4.0–
.0, temperature of 55–65°C, and current density of
of 5 A dm and a temperature of 20°C, the porosity
–
2
decreases from 15 to 9 pores cm as the electrolyte
pH is raised from 1.0 to 4.0. As the pH value is raised
further (to 5.0), the porosity increases to 11 pores cm–2
–
2
–8 Adm .
The strength of coating adherence to the base was
(Fig. 1c).
determined by multiple 90° bending of a coated sample
until its complete fracture in conformity with GOST
9
coating thickness, 20 μm. We examined the outward
appearance of the coatings with an MIM-7 microscope
at ×487.5 magnification. The porosity was determined
by application of filter paper in conformity with
GOST 9.302–88.
As the thickness of a coating deposited at a cathode
–
2
.302–88. The sample size was 25 × 5 × 1 mm, and the
current density of 5 A dm and pH 1.0 increases from 1
to 12 μm, the porosity first sharply decreases and then,
in the range 9–12 μm, varies only slightly. For example,
as the thickness of nickel coatings is raised from 1 to
–2
9 μm, the porosity decreases from 36 to 10 pores cm ,
and when the thickness is raised further to 12 μm, the
–
2
porosity decreases to 8 pores cm .
The phase composition of the nickel coatings was
examined with a DRON-1.5 X-ray diffractometer with
CuKα radiation and a nickel filter. The X-ray diffraction
patterns we obtained were indexed by the Frevel–Rinn
method [9]. The angular correction of the diffractometer
was determined using a reference (quartz). The
scanning rate was 1 deg min . The throwing power of
the electrolyte was studied with a dismountable angled
cathode with an angle of 60° between its sides [10]. The
current efficiency (CE) by nickel and hydrogen was
We studied how the IS in nickel coatings depends
on electrolysis modes (Fig. 2). Measurements were
made at the completion instant of electrolysis. Tensile
stresses were observed. It can be seen in Fig. 2a that,
as the cathode current density is raised from 1 to 5
–
1
–2
A dm , the IS increases from 235 to 245 MPa, and
upon further increase in the current density from 5 to 9
–
2
A dm , decrease from 245 to 225 MPa at an electrolyte
pH 1.0 and temperature of 20°C. As the electrolyte
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 10 2011

1734
BALAKAI et al.
(a)
(a)
–
2
jc, Adm–2
b)
jc, Adm
(b)
(
T, °C
c)
T, °C
c)
(
(
Fig. 2. Internal stress IS of nickel coatings vs. (a) current
density j , (b) electrolyte temperature T, and (c) electrolyte
Fig. 1. Porosity N of nickel coatings vs. (a) cathode current
c
pH. Conditions of a and b are similar to those in Fig. 1.
density j , (b) electrolyte temperature T, and (c) electrolyte
c
–
2
(
c) Temperature 20°C, current density 5 A dm , SBB
pH. Coating thickness 6 μm. (a, b) pH: (1) 1.0, (2) 5.0, and
–1
–
1
concentration 5.0 ml l .
(
(
5
3) 3.0. (a) Temperature 20°C, SBB concentration 5.0 ml l .
–2
b) Current density 5 A dm , pH 3.0, SBB concentration
–
1
–1
.0 ml l . (c) Temperature 20°C, SBB concentration 5.0 ml l .
–1
those for the preceding series, somewhat increases, from
SBB concentration (ml l ): (1) 1.0, (2) 5.0, and (3) 8.0.
2
45 to 255 MPa, and then, upon an increase in pH to 5.0,
sharply grow to 280 MPa (Fig. 2c).
temperature is raised from 20 to 60°C (Fig. 2b), the IS
of 6-μm-thick coatings deposited at a cathode current
At an electrolyte temperature of 20°C and pH 1.0 the
microhardness of nickel coatings first increases from
2500 to 2650 MPa as the cathode current density is raised
–
2
density of 5 A dm and pH 1.0 decreases from 245
to 165 MPa. As pH is raised from 1.0 to 4.0, the IS in
nickel coatings deposited under the same conditions as
–
2
from 1 to 5 A dm , and then, on raising the cathode
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 10 2011

STUDY OF PROPERTIES OF LUSTROUS NICKEL COATINGS
1735
(a)
monodisperse, the amount of inclusions of this kind in
a coating decreases and, therefore, the microhardness
decreases. The possibility of formation of finely
dispersed nickel compounds in the near-cathode layer in
a chloride electrolyte was demonstrated in [3].
The strongest luster of nickel coatings is observed
at those cathode current densities at which the highest
microhardness of deposits is reached. The dependence of
the IS and porosity on the cathode current density is also
confirmed by the dependence of variation of the coating
microhardness in electrolytes containing finely dispersed
compounds of the metal being electrodeposited.
jc, Adm–2
b)
(
According to X-ray diffraction data for coatings
deposited from a low-concentration chloride electrolyte
at pH 1.0, temperature of 20°C, and current densities
–
2
of 1 and 9 A dm , the γ-NiOOH phase is present in the
coatings, but the number of its reflections is substantially
–
2
smaller at 9 A dm . This is also confirmed by the fact
that, as the reduction potential of nickel hydroxide
(–0.720 V) is reached at the cathode, dispersed nickel
compounds start to be incorporated into a coating.
A study of how the electrolyte pH affects the
surface microprofile of nickel coatings deposited
from the chloride electrolyte under study at a cathode
T, °C
Fig. 3. Microhardness H of nickel deposits vs. (a) current
density j and (b) temperature T. (a, b) Coating thickness
0 μm. pH: (1) 1.0, (2) 3.0, and (3) 5.0. (a) Temperature 20°C;
–
2
current density of 5 A dm and temperature of 20°C
demonstrated that the surface of nickel coatings
obtained at pH 1.0 is smoother than that at pH 5.0. The
reason is that the dispersed nickel compounds obtained
in the electrolyte at pH 1.0 are more finely dispersed
than those at pH 5.0. In addition, more finely dispersed
compounds have time to be fully reduced at the cathode
in a larger amount, compared with coarsely dispersed
compounds. Images of nickel coatings deposited from
a low-concentration chloride electrolyte at a temperature
of 20°C and pH 1.0 and 5.0 were obtained with a Quanta
c
2
(
–2
b) current density 5 A dm .
–
2
current density to 9 A dm , decreases to 2400 MPa
Fig. 3a). As the electrolyte temperature is raised
from 20 to 60°C, the microhardness of nickel coatings
deposited at a cathode current density of 5 A dm and
pH 1.0 decreases from 2650 to 2350 MPa (Fig. 3b).
(
–
2
For electrolytes in which metals discharge only
from ions, such a dependence is unusual. However,
for an electrolyte in which finely dispersed compounds
of the metal being electrodeposited are reduced at the
cathode together with ions, the observed dependence
of the coating microhardness on the current density,
presumably, indirectly confirms the specificity of the
cathodic process. If the reduction potential of finely
dispersed particles is not reached yet, or if it is already
reached, but reduction is incomplete because of the
polydispersity of the particles, then the amount of
unreduced particles in a coating grows. This changes
the structure-sensitive properties of the coatings.
After the full reduction potential of finely dispersed
nickel compounds is reached and these compounds are
2
00 scanning electron microscope. Histograms of the
nickel coatings demonstrated that their surface has
a deeper profile at pH 5.0, compared with pH 1.0. The
microprofile of nickel coatings deposited at pH 1.0,
temperature of 20°C, and current density of 5 A dm–2
shows that finer hydroxide inclusions are formed on
the surface, compared with those obtained at a current
–
2
density of 1 A dm . Presumably, this occurs because
the reduction potential of nickel hydroxides is reached
at a higher current density, i.e., the hydroxides are partly
reduced, with the hydroxide inclusions formed on the
surface being finer than those obtained at a low current
density. Because the hydroxides formed at a lower
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 10 2011

1736
BALAKAI et al.
current density have not enough time to be reduced, the
inclusions produced in this case are coarser.
Properties of nickel coatings deposited from the chloride
electrolyte under study and sulfate-chloride electrolyte
(GOST 9.305–84)
The corrosion resistance was determined using the
Corrodcote technique. Coatings deposited from a low-
concentration chloride electrolyte compare well in cor-
rosion resistance with coatings deposited from the wide-
ly industrially used sulfate-chloride electrolyte (electro-
lyte no. 2, GOST 9.305–84) containing 1,4-butynediol
as a luster-forming additive. The electrolyte had the fol-
Values of parameters for a coating
deposited from indicated electrolyte
Parameter
sulfate-chloride
chloride no. 1
no. 2
–
1
Microhardness,
MPa
2350–2650
165–280
9–15
1900–2100
125–190
13–18
lowing composition (g l ): nickel sulfate heptahydrate
2
1
50–300, boric acid 25–40, sodium chloride 10–15,
,4-butynediol 0.2–0.5, formalin 0.5–1.2, and chlora-
Internal stress,
MPa
mine B 2.0–2.5. The deposition was carried out at pH
.5–5.5, electrolyte temperature of 40–50°C, and cath-
4
Porosity at a
–
2
ode current density of 2.5–3.5 A dm . The adhesion of
nickel coatings deposited from the chloride electrolyte
to the base of steel, copper, and copper alloys satisfies
GOST 9.302–88.
thickness of 6 μm,
–
2
pores cm
Adhesion to a base
made of steel,
copper, and copper
alloys
Satisfies GOST 9.302–88
The chloride lustrous-nickel-plating electrolyte
compares well in throwing power with sulfate-
chloride lustrous-nickel-plating electrolytes containing
Current efficiency
92–96
93–98
1
,4-butynediol as a luster-forming additive. As the
by nickel, %
–
2
cathode current density is raised from 0.5 to 9 A dm ,
the throwing power of the low-concentration chloride
electrolyte decreases from 26 to 16% at pH 1.0, and
from 22 to 13% at pH 5.0.
Luster, %
96–99
13–26
90–92
8–14
Throwing power,
%
The properties of nickel coatings deposited from the
chloride electrolyte under study were compared with
those of nickel coatings deposited from a sulfate-chloride
electrolyte containing 1,4-butynediol (GOST 9.305–84)
for heating a bath to the necessary temperature, and
permanent control over the electrolyte temperature.
The electrolyte developed in the study operates at both
elevated and room temperatures.
(see the table). It can be seen in the table that the nickel
coatings deposited from the low-concentration chloride
electrolyte (electrolyte no. 1) surpass those deposited
from the sulfate-chloride electrolyte (electrolyte no. 2) in
microhardness and luster, are about the same in porosity,
adhesion, and current efficiency; and are inferior to the
latter only in the IS. The throwing power of the chloride
electrolyte is somewhat higher than that of the sulfate-
chloride electrolyte.
It is desirable to maintain the current density within
–
2
the range 0.5–5 A dm at a temperature of 20°C and
–
2
1–12 Adm at 60°C.
The chloride lustrous-nickel-plating electrolyte was
used in a 500-l bath. The electrolyte was adjusted on
taking into account the passed amount of electricity
–1
(
A h l ). Upon a prolonged operation of the electrolyte
–
1
–1
–1
Use of a chloride nickel-plating electrolyte diluted
in its main component will make it possible to diminish
the content of nickel ions in wastewater and to develop
low-waste and waste-free technologies. Industrial
electrodeposition of lustrous nickel coatings mostly
employs electrolytes operating at elevated temperatures
with 80 A h l , 1.5 ml l of SBB and 0.4 g l of
chloramine B was added. The main components of the
electrolyte were adjusted once in a month on the basis
of the results of a chemical analysis. For an electrolyte
operating at 60°C, the solution volume was brought to
the initial level not rarer than once in 1–2 shifts, with
the pH value simultaneously adjusted. Water used
for this purpose was taken from the first uncirculated
washing bath (catching bath), which saves salts carried
(40–60°C).This leads to an increased energy expenditure
and faster evaporation of water from baths and requires
permanent electrolyte adjustment, additional time
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 10 2011

STUDY OF PROPERTIES OF LUSTROUS NICKEL COATINGS
1737
away by articles from the nickel-plating bath. To obtain
REFERENCES
high-quality deposits, the electrolyte was subjected to
chemical and selective purification not rarer than once
in 1.5–2 months.
1. Gran’, T.V. and Kheifets, V.L., Tsv. Met., 1964, no. 4,
pp. 22–26.
2
3
4
. Kheifets, V.L. and Gran’, T.V., Elektroliz nikelya
Electrolysis of Nickel), Moscow: Metallurgiya, 1975.
(
CONCLUSIONS
. Balakai, V.I., Arzumanova, A.V., and Balakai, K.V., Zh.
Prikl. Khim., 2010, vol. 83, no. 1, pp. 67–73.
(
1) It was shown that the dependence of the
. Zhukov, I.I., Izbrannye trudy (Selected Works),
Leningrad: Akad. Nauk SSSR, 1952, pp. 297–307.
microhardness, internal stress, and porosity on the
–
2
cathode current density (1–9 A dm ) has an extremal
nature. The maximum values of microhardness, internal
stress, and porosity are 2650 MPa, 245 MPa, and
5
6
. RF Patent 2213810.
. Yampol’skii, A.L. and Il’in, V.A., Kratkii spravochnik
gal’vanotekhnika (Concise Electroplater’s Handbook),
Leningrad: Mashinostroenie, 1981.
–2
1
5 pores cm , respectively. The manner in which these
physicomechanical properties of nickel coatings depend
on the pH value and temperature of the electrolyte was
determined and quantitative results were presented.
7
8
. Popereka, M.Ya., Vnutrennie napryazheniya elektro-
liticheski osazhdaemykh metallov (Internal Steresses
in Electroplated Metals), Novosibirsk: Nauchno–Sib.
Knizhn. Izd., 1966.
(
2) It was found that nickel coatings deposited from
a low-concentration chloride electrolyte (electrolyte no.
) compare well in corrosion resistance with coatings
deposited from the sulfate-chloride electrolyte widely
used in the industry [electrolyte no. 2, GOST (State
Standard) 9.305–84].
. Bobylev, A.V., Mekhanicheskie i tekhnologicheskie svoi-
stvametallov:Spravochnik(MechanicalandTechnological
Properties of Metals), Moscow: Metallurgiya, 1980.
1
9. Gorelik, S.S., Rastorguev, L.N., and Skakov, Yu.A.,
Rentgenografi h ce skii elektronnoopticheskii analiz
X-ray Diffraction and Electronic-Optical Analyses),
i
(
(
3) It was demonstrated that the throwing power of
the low-concentration chloride electrolyte is within the
range 13–26%.
Moscow: Metallurgiya, 1970.
1
0. Tsupak, T.E., Novikov, V.T., Nachinov, G.N., and Vagra-
myan, T.A., Laboratornyi praktikum po tekhnologii elek-
trokhimicheskikh pokrytii: Uchebnoe posobie (Practical
Laboratory Works on Technology of Electrochemical
Coatings), Moscow: Khimiya, 1980.
(
4)Technological recommendations for industrial use
of the suggested chloride electrolyte for lustrous nickel
plating were substantiated and confirmed in practice.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 10 2011