Applied Surface Science 372 (2016) 1–6

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Applied Surface Science

journal homepage: www.elsevier.com/locate/apsusc

Effects of choline chloride on electrodeposited Ni coating from a

Watts-type bath
Yurong Wang a , Caihong Yang a , Jiawei He a , Wenchang Wang a , Naotoshi Mitsuzak e ,
Zhidong Chen b,c,d,∗
a
School of Petrochemical Engineering, Changzhou University, Changzhou 213164, China
b
School of Material Science and Engineering, Jiangsu Key Laboratory of Materials, Surface and Technology, Changzhou University, Changzhou 213164,
China
c
Jiangsu Collaborative Innovation Center of Photovoltaic Science and Engineering, Changzhou University, Changzhou 213164, China
d
Jiangsu Key Laboratory of Advanced Catalytic Material and Technology, Changzhou University, Changzhou 213164, China
e
Qualtec Co., Ltd, Osaka 590-0906, Japan

a r t i c l e i n f o a b s t r a c t

Article history: Electrodeposition of bright nickel (Ni) was carried out in a Watts-type bath. Choline chloride (ChCl) was
Received 2 October 2015 applied as a multifunctional additive and substitute for nickel chloride (NiCl2 ) in a Watts-type bath. The
Received in revised form 19 January 2016 function of ChCl was investigated through conductivity tests, anodic polarization, and cathodic polariza-
Accepted 22 January 2016
tion experiments. The studies revealed that ChCl performed well as a conducting salt, anodic activator,
Available online 23 January 2016
and cathodic inhibitor. The effects of ChCl on deposition rate, preferred orientation, grain size, surface
morphology, and microhardness of Ni coatings were also studied. The deposition rate reached a maximum
Keywords:
value of greater than 27 ␮m h−1 when 20 g L−1 ChCl was introduced to the bath. Using X-ray diffraction, it
Additives
Choline chloride was confirmed that progressive addition of ChCl promoted the preferred crystal orientation modification
Electroplating from (2 0 0) and (2 2 0) to (1 1 1), refined grain size, and enhanced microhardness. The presence of ChCl
Nickel lowered the roughness of the coating.
Preferred orientation © 2016 Elsevier B.V. All rights reserved.

1. Introduction smooth film. Meng et al. [11] demonstrated that the addition of
phytic acid favored the growth of nano-scale twins in the inte-
Electroplated nickel (Ni) is extensively used in engineering rior of the grains of Ni coating and could improve the corrosion
applications due to its excellent corrosion and wear resistance, resistance. Sezer et al. [12] revealed that using N,N-dimethyl-
easy mechanical operation, and good electromagnetic character- N-2-propenyl-2-propene-1-ammonium chloride-2-propenamide
istics [1,2]. As is known to all, the structural characteristics and (PQ7) as a surfactant provided the possibility of obtaining Ni coat-
mechanical properties of Ni coating are closely related to the plating ings with high plating rate, high leveling, and low particle size.
parameters, such as bath component [3], current density [4], addi- The effect of the additive on Ni coating is highly dependent on
tives [5–9], etc. Nevertheless, under certain suitable conditions, the functional groups present in their structures. For examples, the
additives have a more profound influence on deposition proper- additives containing hydroxyl groups, such as 2-butyne-1,4-diol [8]
ties than any other plating variables [5]. Thus, more effort has been and glycerol [10], usually serve to brighten Ni coating. Compounds
placed toward applying new additives to Ni electroplating bath containing quaternary ammonium functional group, such as PQ7
[10–15]. [12] and benzyl-dimethyl-alkyl ammonium chlorides [16], play a
Oloveira et al. [10] studied the effects of glycerol, manni- role of leveling Ni coating surface and inhibiting the cathode Ni
tol and sorbitol finding that the presence of polyalcohols in deposition. NiCl2 behaves as a conducting salt while the chloride
the electrolytic solution could significantly improve the stability ion acts as an anodic activator is commonly applied in Ni electro-
of the bath and achieve good leveling properties to produce a plating bath [17]. In this context, this work aims to explore the
feasibility of designing or screening a compound containing various
functional groups to serve as a multifunctional additive to simplify
the electroplating bath and improve the performance of Ni coating.
∗ Corresponding author at: School of Material Science and Engineering, Jiangsu
Choline chloride (ChCl, 2-hydroxyethyltrimethylammonium
Key Laboratory of Materials, Surface and Technology, Changzhou University,
Changzhou 213164, China. chloride, (CH3 )3 N(Cl)CH2 CH2 OH), a cheap, biodegradable, and safe
E-mail address: zdchen.lab@gmail.com (Z. Chen). quaternary ammonium salt, has been widely applied to metal Ni

http://dx.doi.org/10.1016/j.apsusc.2016.01.182
0169-4332/© 2016 Elsevier B.V. All rights reserved.
2 Y. Wang et al. / Applied Surface Science 372 (2016) 1–6

Table 1 scanning electron microscope (SEM, JSM-6360LA, Japan Electron

Composition and operating conditions for Ni electroplating.
Optics Laboratory Co. Ltd., Japan), respectively. The roughness of
Bath composition Operation conditions the Ni coatings was tested by optical stylus profilometer (Contour
NiSO4 • 6H2 O (g L−1 ) 200 pH 4.0 GT, Bruker Corporation, USA).
H3 BO3 (g L−1 ) 30 Temperature (◦ C) 30 In order to describe the structure and estimate quantitatively
ChCl (g L−1 ) 0–200 Current density (A dm−2 ) 2 the preferred orientation of the Ni deposits, the relative texture
a
Time (min) 10 coefficient RTC(h k l) was calculated, which is defined as [14]:
a
60 min for microhardness test.
0
I(h k l)/I(h k l)
RTC(h k l) = × 100% (1)
[18,19] and its alloys [20,21] electrodeposition in the form of deep 
3
0
I(h k l) /I(h
eutectic solvents (DESs). Recently, our group applied ChCl both as a k l)
solvent and a ligand to conduct electroless silver [22], tin [23], gold 1
[24], and palladium [25] deposition in ChCl-H2 O solutions. All the
where I(h k l) are the diffraction intensities of the (h k l) lines
coatings exhibited bright surfaces and satisfactory performance. 0
measured in the diffractogram of the deposit and I(h are the cor-
ChCl contains Cl− , quaternary ammonium and hydroxyl functional l k)
groups. Thus, it could be a good multifunctional additive to simplify responding intensities of a standard Ni powder sample randomly
the electroplating bath and improve the performance of Ni coating. oriented from JCPDS 04-0850. The summation in the denominator
Applying ChCl to Ni electrodeposition from aqueous solution has is taken for the three “basic” lines visible in the diffraction pattern,
not reported up to now. i.e. (1 1 1), (2 0 0), and (2 2 0). A preferred orientation through an
In the present work, ChCl has been introduced to the most axis (h k l) is indicated by the value of RTC ≥ 16.7%.
widely used Watts-type bath as a novel multifunctional additive. The crystal grain size of Ni coating was calculated through the
The roles of ChCl in the plating bath and the effects on Ni coating Scherrer equation [26] on the basis of the Ni (1 1 1) line from the
have been investigated through the techniques of electrochemistry XRD.
and surface analysis, respectively.
3. Results and discussion
2. Experimental
3.1. Features of ChCl in plating bath
2.1. Electrodeposition procedure of Ni coating
Firstly, as a quaternary ammonium salt, ChCl contains con-
The electroplating was carried out in a Taflon rectangular cell ducting power. Experiments were carried out to measure the
(8 cm × 6 cm × 5 cm) containing Watts-type bath with different conductivity of the plating bath with different ChCl concentrations
amount of ChCl. A Ni plate (50 mm × 150 mm × 2 mm) and a Cu (CChCl ) at room temperature. The results showed that the conduc-
sheet (20 mm × 50 mm × 0.2 mm) were used as the anode and tivity increased linearly from 46.6 mS cm−1 to 78.2 mS cm−1 with
cathode, respectively, at a distance of 80 mm. The plating bath com- the increasing CChCl from 0 to 50 g L−1 . The linear regression equa-
position and operating conditions are listed in Table 1. All solutions tion for the linear part of the plotted CChCl – Conductivity curve
were prepared with analytic grade reagents and distilled water. was established. The slope, intercept and square of the correlation
Before electroplating, Cu sheets were treated in alkali and acid solu- coefficient of the equation were 0.622, 46.7 and 0.9989, respec-
tions to be degreased and micro-etched, respectively. After each of tively. In contrast, the conductivity of Watts bath containing varied
the pretreatment steps, the substrates were rinsed with distilled NiCl2 • 6H2 O concentration (CNiCl2 , all the following mentioned NiCl2
water and dried through air flow. are referred to NiCl2 • 6H2 O) from 0 to 50 g L−1 was also tested. It was
found that the conductivity increased with CNiCl2 and reached the
2.2. Instruments and methods maximum of 75.0 mS cm−1 when CNiCl2 increased to 50 g L−1 , which
is about 1.17 times as many the mole ratio of Cl− in NiCl2 as in ChCl.
Conductivity was measured using a conductivity meter (DDS-
11A, Shanghai Kangning Electric Light Technology Co. Ltd., China).
The microhardness property was analyzed using a microhardness
tester (HXD-1000TMC/LCD, Shanghai Taiming Optical Instrument
Co. Ltd., China) with a diamond pyramid indentor at a load of 200 g
for 15 s.
Electrochemical measurements were conducted on an electro-
chemical workstation (CHI660D, Beijing Huake Putian Technology
Co. Ltd., China). The anodic polarization and cathodic polarization
experiments were conducted in the plating solution as was shown
in Table 1. The counter electrode and the reference electrode were a
platinum plate (10 mm × 10 mm) and saturated calomel electrode
(SCE), respectively. The working electrode was a Ni plate anode
and a platinum wire electrode for anodic polarization and cathodic
polarization experiments, respectively. The potential was scanned
at a constant scan rate of 5 mV s−1 .
The thickness of Ni coating was measured by energy dispersive
X-ray spectroscopy (EDX, EDX1800, Skyray Instrument Co. Ltd.,
China). Structure and surface morphology of the deposited Ni
coating were investigated by X-ray diffraction (XRD, Rigaku D/max
2500 powder diffractometer, Cu K␣ ( = 1.542◦ A) radiation at Fig. 1. Effect of ChCl on anode polarization of nickel electrodeposition in comparison
30 kV and 40 mA, scan rate at 6◦ min−1 , 2 from 10◦ to 80◦ ) and with Watts bath containing 20 g L−1 NiCl2 . Conditions are shown in Table 1.
 Y. Wang et al. / Applied Surface Science 372 (2016) 1–6 3

Fig. 2. Effect of ChCl on cathode polarization of Ni electrodeposition in comparison Fig. 3. Effect of ChCl on the deposition rate. Other conditions are as shown in Table 1.
with Watts bath containing 20 g L−1 NiCl2 . Conditions are shown in Table 1.

So it can be concluded that Watts-type bath with ChCl has better

conducting power than Watts bath with NiCl2 . the effect of ChCl on the cathode in comparison with NiCl2 . As can
Secondly, the presence of Cl− can improve the activity of the be seen from Fig. 2, all the polarization curves shifted negatively
Ni plate electrode, the current efficiency, and anodic dissolution with the addition of ChCl, nevertheless, the slope of polarization
[17,27]. Thus, the anodic polarization curves were constructed curves increased with the increasing CChCl from 20 g L−1 to 50 g L−1 .
to see the effect of ChCl on anode in comparison with NiCl2 . As It exhibited the largest cathodic polarization effect on the condi-
can be seen in Fig. 1, anodic dissolution current was almost zero tion of 10 g L−1 ChCl. The reason for decreased cathodic polarization
unless ChCl or NiCl2 was presented in the bath. The polarization with the increasing CChCl is perhaps due to the ability of depolariza-
curves shifted positively and the current density increased with the tion by Cl− on the cathode. Therefore, the more ChCl presented
increasing CChCl in plating bath. However, comparing both ChCl and in the plating bath, the more Cl− released, and the weaker the
NiCl2 at the same mass amount of 20 g L−1 , ChCl exhibited stronger polarization was. In contrast, the presence of NiCl2 brought about
anodic polarization effect than NiCl2 . Therefore, ChCl has the func- potential shifting positively, which suggests depolarization on the
tion of increasing anodic activation and may be a good substitute cathode. Hence, it’s not hard to see that it’s necessary for Watts
for NiCl2 . bath to add organic additives to conduct cathodic polarization for
Finally, the quaternary ammonium group has the ability of obtaining refined coatings, while in our Watts-type bath, ChCl may
cathodic polarization and inhibiting the deposition of metals [28]. play the role of additives, and organic additives might not be needed
Thus, the cathodic polarization curves were also performed to see any more.

Fig. 4. Effect of ChCl on XRD patterns of Ni coatings. Other conditions are shown in Table 1.
4 Y. Wang et al. / Applied Surface Science 372 (2016) 1–6

3.2. Effect of ChCl on Ni coating

Since ChCl had multiple effects in Watts-type bath, it should

have an influence on Ni coating in turn. Here, the commonly used
organic additive, pyridinium propyl sulphobetain ((1-pyridinio)-
1-propanesulfonate, C8 H11 O3 NS, PPS), which has the similar
quaternary ammonium group as ChCl, and NiCl2 were applied for
comparison.

3.2.1. Effect on the deposition rate

Effect of ChCl on deposition rate is shown in Fig. 3. It was
observed that ChCl had significant influence on deposition rate.
With ChCl being absent in the plating solution, the deposition
rate showed the slowest level, for the reason that no anodic
activation occurred without Cl− . With the increasing CChCl , the
deposition rate was speeded up until CChCl reached 20 g L−1 . This
was due to the raised Cl− concentration and promoted anodic acti-
vation. Then, the deposition rate slowed down with the increasing
CChCl . The reasons could be accounted for by two aspects. On one
hand, the increased CChCl will make the viscosity of the plating Fig. 5. Variation of RTC(h k l) for different diffraction peaks with the varied CChCl .

solution greater and greater. As a result, the ability of ions migra-

tion in plating solution decreased [24]. On the other hand, ChCl The relationship between ChCl and orientation identified as
would be absorbed onto the surface of the cathode to prevent RTC(h k l) is shown in Fig. 5. The preferred orientation was (2 0 0)
Ni2+ from electrolysis. Thus, the deposition rate of Ni deposition and (2 2 0) when ChCl was absent in the plating solution. Nev-
decreased. ertheless, the increasing CChCl from 10 g L−1 to 40 g L−1 brought
on decreasing predomination of (2 0 0) and (2 2 0) crystal orien-
3.2.2. Effect on Ni crystal structure tation, and increasing predomination of (1 0 0) crystal orientation
The XRD patterns of Ni coatings deposited from plating solutions sharply. While further increasing CChCl had no significant effect on
containing varied CChCl were presented in Fig. 4. Crystal structure the RTC(1 1 1) , RTC(2 0 0) , and RTC(2 2 0) . The preferred crystal orienta-
could be deduced from the sharp diffraction and smooth baseline. tion changing from (2 0 0) to (1 1 1) is similar to what Rashidi et al.
The diffraction peaks at 44.5◦ , 51.3◦ , and 76.4◦ are attributed to [29] presented. However, RTC(1 1 1) showed almost double that of
Ni (1 1 1), (2 0 0), and (2 2 0) crystalline facet, respectively. With Rashidi reported where saccharin was used as additive. For com-
the increasing CChCl , the intensity of X-ray scattered from (1 1 1) parison, XRD pattern of Ni coating deposited from saccharin-free
phase increased, whereas for (2 0 0) and (2 2 0) phases decreased. Watts baths containing 20 g L−1 NiCl2 was taken. It showed that tex-
The results indicate that the crystallographic orientation was ture (2 0 0) exhibited predominating over (1 1 1) and (2 2 0) crystal
not randomly oriented, but grew at a specific orientation and orientation at RTC(2 0 0) of 89%, which is similar with Ref. [30], where
significantly influenced by CChCl . the preferred orientation was texture (2 0 0) as well.

Fig. 6. SEM images of Ni coatings deposited from Watts-type baths containing different CChCl . (a) 0 g L−1 ; (b) 10 g L−1 ; (c) 20 g L−1 ; (d) 30 g L−1 ; (e) 40 g L−1 ; (f) 50 g L−1 ; (g)
70 g L−1 ; (h) 100 g L−1 ; (i) 150 g L−1 ; (j) 200 g L−1 .
 Y. Wang et al. / Applied Surface Science 372 (2016) 1–6 5

Table 2
Roughness of the Ni coatings obtained by electrodeposition from solutions (a) with-
out ChCl, (b) with 20 g L−1 ChCl, and (c) with 0.1 g L−1 PPS.

Samples a b c
a
Roughness Ra (␮m) 9.47 ± 0.39 8.04 ± 0.20 8.59 ± 0.13

a
Every sample was tested for 5 ran-dom points, Ra is the average results of 5
points.

microhardness of Ni coating followed the direct Hall–Petch relation

[32], which is that microhardness of a material has a linear depend-
ency with the reciprocal square root of grain size for a certain grain
size.

3.2.4. Effect on roughness

Considering the experimental result that the surface of Ni coat-
ing was rough and dim with 20 g L−1 PPS, the following comparative
experiments were carried out between 20 g L−1 ChCl and 0.1 g L−1
PPS (0.1 g L−1 is the typical amount added in Ni electroplating solu-
Fig. 7. Effect of ChCl on the crystal grain size. Other conditions are as shown in tion). The roughness of Ni coatings obtained from the solutions as
Table 1. without ChCl, with 20 g L−1 ChCl, and with 0.1 g L−1 PPS, respec-
tively, was investigated to verify the function of ChCl as brightener
Fig. 6 shows the influence of ChCl on the surface morphology of (see Table 2). It was observed that with the presence of ChCl and
Ni coatings. It can be seen that the surface was refined and the grain PPS, the values of the average roughness Ra of the coatings were
size decreased simultaneously with the increasing CChCl . According lower than that from the solution without additives. Furthermore,
to the Debye–Scherrer equation, Ni crystal grain size could be cal- Ra of the coating obtained from the solution with ChCl was even
culated from XRD data. On the basis of the Ni (1 1 1) line from Fig. 4, lower than the coatings deposited from the solution with PPS at the
the grain sizes of Ni coatings were calculated and plotted in Fig. 7. value of 8.04 ␮m. Thus, it could be say that ChCl could be served as
The grain size decreased with the increasing CChCl , which was in brightener.
accordance with the results shown in Fig. 4. The refined surface
and decreased grain size may be attributed to the roles of quater- 4. Conclusions
nary ammonium group and hydroxyl group in ChCl. The organic
compounds with two such functional groups were always applied In this content, ChCl was applied as a new multifunctional
as additives to brighten and refine grain size [11,10]. additive to simplify the electroplating bath and improve the
performance of Ni coating in a Watts-type bath, proven by electro-
3.2.3. Effect on microhardness chemical and surface analytic techniques. It was found that ChCl
As described above that an increase in CChCl produced a could be applied as a conducting salt, anodic activator, cathodic
decreased in grain size of Ni coating, therefore ChCl could also influ- inhibitor, and brightener simultaneously. The deposition rate had
ence the microhardness of the coating. It can be seen from Fig. 8 that the maximum value of higher than 27 ␮m h−1 when 20 g L−1 ChCl
the microhardness of Ni coatings increased dramatically with the presented in the bath. The concentration of ChCl larger than 30 g L−1
increasing CChCl until CChCl reached 50 g L−1 , and then slowed down could lead (1 1 1) crystal orientation to predominate over (2 0 0) and
the increasing trend. This phenomenon can be attributed to the (2 2 0) crystal orientations. Texture (1 1 1) kept dominant steadily
higher texture coefficient of (1 1 1) [31] and the continually reduced when the concentration of ChCl was larger than 40 g L−1 . Contin-
grain size of Ni coating (see the insert part of Fig. 8). In our case, the uously increased the concentration of ChCl could refine the grain
size and enhance the microhardness constantly. Presence of ChCl
could lower the roughness of the Ni coating.

Acknowledgements

The authors greatly acknowledge financial support from

National Natural Science Foundation of China (Grant No. 51401038,
51574047), Foundation of Jiangsu Educational Committee (Grant
No.13KYB150004).

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