The paper presents the electrochemical obtaining of nickel matrix composite coatings using kaolin particles as dispersed phases. Watts electrolytes were used, with a pH = 4.5 current densities of 6, 9, 12 A/dm2 , a dispersed phase concentration of 20 g/L, shaking speeds of 500, 700 and 900 rpm, deposition time of 60 minutes. Their characterization has been achieved both from a microstructural point of view and from the point of view of layer thickness, microhardness and behaviour in salt mist corrosion. The presence of dispersed phase particles, which acted as nucleation centres, led to the reduction of the nickel crystallites, which further decreased the roughness of the coatings while increasing hardness. By correlating the current density with the rate of stirring, respectively the increase their, thicker layers were obtained

Simona BOICIUC

The Annals of “Dunarea de Jos” University of Galati Fascicle IX Metallurgy and Materials Science

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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
No. 1 - 2018, ISSN 1453-083X 
 
 
 
 
STUDIES AND RESEARCHES ON OBTAINING 
ELECTROCHEMICAL COMPOSITE COATINGS 
 IN NICHEL - Ni / KAOLIN MATRIX 
 
Simona Boiciuc 
“Dunarea de Jos” University of Galati 
e-mail: simonaboiciuc@yahoo.com 
 
ABSTRACT 
 
The paper presents the electrochemical obtaining of nickel matrix composite 
coatings using kaolin particles as dispersed phases. Watts electrolytes were used, 
with a pH = 4.5 current densities of 6, 9, 12 A/dm2, a dispersed phase concentration 
of 20 g/L, shaking speeds of 500, 700 and 900 rpm, deposition time of 60 minutes. 
Their characterization has been achieved both from a microstructural point of view 
and from the point of view of layer thickness, microhardness and behaviour in salt 
mist corrosion. The presence of dispersed phase particles, which acted as 
nucleation centres, led to the reduction of the nickel crystallites, which further 
decreased the roughness of the coatings while increasing hardness. By correlating 
the current density with the rate of stirring, respectively the increase their, thicker 
layers were obtained. 
 
KEYWORDS: Ni composite coatings, electrodeposition, kaolin, 
microhardness 
 
1. Introduction 
 
The field of composite materials is in a rapid 
and continuous expansion due to the large number of 
possible combinations between two or more 
components and the advantage of obtaining a wide 
range of materials the use of which can be expanded 
in almost all technical fields (aerospace, naval, 
automotive, electrical and electronics industries) as a 
result of the possibility of modelling their structure 
and properties. In this respect, the following 
properties are to be improved: hardness, wear 
resistance, high temperature resistance, dimensional 
stability, corrosion resistance, vibration damping 
capacity, lubrication [1, 2, 4, 5]. 
ACE electrochemical composite coatings have a 
number of advantages such as high deposition 
velocity (rate), simple automation equipment, easy 
control of microstructure and thickness deposition 
(from nanometer to micrometric level), uniform 
coverage capability of both complicated geometry 
surfaces and large ones [1, 2, 4, 5]. 
Ni - kaolin composite materials are used in the 
aerospace, automotive industry, in applications 
requiring good behavior to wear, abrasion, fatigue, 
corrosion [3]. 
The properties of the composite materials 
depend on the type, structure, shape, size, 
morphology and content of the complementary phase 
particles, as well as their distribution in the metal 
matrix. 
The functional properties of composite coatings 
are strongly influenced by their structure, tensions 
developed in the layer as well as by the orientation of 
the complementary phases which can determine the 
anisotropy of the properties. 
Nickel was chosen as a coating material because 
it is one of the most common industrial coatings used 
for decorative and functional applications [4]. 
Kaolin - Al2O3*2SiO2*2H2O - is a very fine 
grain, white 2.65 g/cm3 density clay (mineral) of 
low-plasticity, high temperature resistance and by 
burning it turns solid and very compact. A mineral 
layer has a triclinic crystalline symmetry made up of 
octahedral Al2O3 and tetrahedral formations of SiO2 
that share a common plan formed by oxygen atoms. 
The layers thus formed are linked together by 
hydrogen atoms [bonds] [3]. The mechanical 
properties of the composite materials depend on their 
microstructure (nanocrystalline, microcrystalline), 
correlating with dislocation theory, strength and 
ductility. The addition of dispersed phase particles in 
order to obtain composite materials acts as a barrier 
against the displacement of dislocations followed by 
blocking them at the grain boundary which results in 
increased resistance to deformation and hardness [6]. 
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
No. 1 - 2018, ISSN 1453-083X 
 
 
 
 
Fig. 1. Crystalline structure of kaolin [3] 
 
The research carried out in this paper has as a 
general objective the development of a technology 
for the electrochemical production of composite 
coatings in nickel matrix using as dispersed phase 
kaolin particles with dimensions of approx. 2 μm and 
their characterization in terms of microstructure, layer 
thickness, microdurity and behaviour in salt mist 
corrosion. 
 
2. Experimental research 
 
To obtain nickel coatings and composite 
coatings in a nickel matrix, a DC source, a device 
provided with a magnetic stirrer and a bath 
temperature control system with an electrolyte 
receptacle were employed. A volume of 300 ml 
solution was used and the experiments were carried 
out at 50 oC. 
Watts electrolytes consisting of NiSO4 6H2O – 
300 g/L, NiCl2 6H2O – 50 g/L and H3BO3 – 40 g/L, 
pH = 4.5 current densities of 6, 9, 12 A/dm2, a 
dispersion phase concentration of 20 g/L, stirring 
speeds of 500, 700 and 900 rpm, with a 60 minutes 
deposition time. 
The electrodeposition was achieved by vertical 
alignment of the electrodes at a distance of 14 mm 
from each other. As anode, high purity nickel (99%) 
was used, the cathode being copper strip, 
representing the support material for 76 x 20 x 1 mm 
coatings. 
The copper band used was prepared by 
degreasing (organic solvents - trichlorethylene), 
pickled (HNO3 + HCl at room temperature for 1-2 
minutes) followed by washing with distilled water. 
The metallographic analysis of the samples was 
carried out on a Neophot 2 microscope, with the 
acquisition of data on the computer and revealed the 
appearance of the nickel deposition surface compared 
to the composite coatings, their adhesion, the way 
electrodes have grown, as well as the presence of 
defects such as pores, cracks, exfoliations. The EDS 
analysis was performed with a SEM Quanta 200 
electronic scanning microscope provided with an 
energy dispersion spectrometer. 
To determine the microdurity, the PMT-3 
micro-hardness durimeter was used with a load of 50 
g. 
The corrosion behavior in salt mist of the 
composite layers was performed according to ISO 
9227/2012 for a period of 96 hours. For the test, the 
sodium chloride solution was prepared by dissolving 
in distilled water with a conductivity of less than or 
equal to 20 µS/cm2 at 25  2 oC, of a quantity of 
sodium chloride to give a concentration of 50 ± 5 g/L. 
The relative density of a solution with this 
concentration is between 1.00255 and 1.0400. The 
pH of the saline solution was adjusted so that the pH 
of the solution collected in the spraying chamber 
ranged between 6.5 and 7.2. This was measured with 
a pH meter HI 991001, produced by "Hanna 
Instruments", also provided with a temperature 
indicator. 
 
3. Experimental Results 
 
Characterization of composite coatings in 
nickel matrix with dispersed phase 
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
No. 1 - 2018, ISSN 1453-083X 
 
 
Al2O3*2SiO2*2H2O kaolin obtained 
electrochemically 
Characterization of ACE composite coatings 
was performed compared to pure nickel coatings and 
consisted of macro and microstructural analysis, layer 
thickness and micro hardness determinations. 
Fig. 1 shows the appearance of pure nickel 
coatings for different current densities and different 
agitation/stirring rates. It can be seen that the 
deposited layers are homogeneous, without cracked 
and have good adhesion to the copper supports. It can 
also be seen that increasing the density of the current 
increases the thickness of the obtained layer, keeping 
the temperature and deposition time constant. 
Increasing the current density leads to the formation 
of finer structures as a result of the multiplication of 
the crystallization germs on the cathode. 
This influence of the current density can be 
explained by increasing the active surface of the 
cathode, the crystalline germs being formed on the 
inactive parts of the less active cathode [5]. 
As to the influence of the stirring speed 
(correlated with the current density), it has been 
found that when this grows compact, smooth, fine 
grain deposits of a high current efficiency can be 
obtained; the higher the current density, the more 
stirring should be done. 
The primary role of stirring/agitation is to favour 
the homogenization of the ionic concentration in the 
cathode film and in the rest of the solution. It 
maintains the concentration of the solution constant, 
avoiding concentration polarization. 
Fig. 2 shows the microstructural aspect of the 
electrochemical composite coatings in nickel matrix 
using kaolin particles as dispersed phase. 
Analysing Fig. 2 it can be seen that the 
electrochemically obtained composite coatings in 
nickel matrix using kaolin particles as dispersed 
phase exhibit good homogeneity and compactness. 
Increasing the current density increases the degree of 
inclusion of the dispersed phase. 
The kaolin particles led to the decrease of the 
crystallites' dimensions (compared to the pure nickel 
deposits) which further led to the decrease in the 
roughness of the deposits and the increase of the 
hardness (concomitantly blocking the displacement of 
the dislocations in the nickel matrix) (Fig. 7). 
For the current density of 6 A/dm2 it was 
considered that the optimal deposition regime was 
that of sample P3 (Dcrt = 6 A/dm2, v = 900 rpm, t = 60 
minutes). At low stirring rates and low current 
densities (P1, P2), the growth rate of the crystalline 
germs exceeds the germination rate, which results in 
larger, less homogeneous and less compacted 
macrocrystalline deposits. 
For the current density of 9 A/dm2 it was 
considered that the optimal deposition regime was 
that of the P6 sample (Dcrt = 9 A/dm2, v = 900 rpm, t 
= 60 minutes). This has led to a compact, 
homogeneous, adherent deposit. As the current 
density increases, the germination speed increases 
and leads to more and more microcrystalline, fine-
grained deposits. 
 
 
 
 
P01 – 6 A/dm2, v = 500 rpm, 60 minutes  
 
P01 – 6 A/dm2, v = 500 rpm, 60 minutes 
 
5 m 10 m 
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
No. 1 - 2018, ISSN 1453-083X 
 
 
 
P05 – 9 A/dm2, v = 700 rpm, 60 minutes 
 
P05 – 9 A/dm2, v = 700 rpm, 60 minutes 
 
P09 – 12 A/dm2, v = 900 rpm, 60 minutes 
 
P09 – 12 A/dm2, v = 900 rpm, 60 minutes 
 
Fig. 1. Microstructural appearance of pure nickel coatings 
 
 
P3 – 6 A/dm2, v = 900 rpm, 60 minutes 
 
P3 – 6 A/dm2, v = 900 rpm, 60 minutes 
5 m 10 m 
10 m 5 m 
10 m 5 m 
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
No. 1 - 2018, ISSN 1453-083X 
 
 
 
P6 - 9 A/dm2, v = 900 rpm, 60 minutes 
 
P6 - 9 A/dm2, v = 900 rpm, 60 minutes 
 
P7 - 12 A/dm2, v = 500 rpm, 60 minutes 
 
P7 - 12 A/dm2, v = 500 rpm, 60 minutes 
 
Fig. 2. The microstructural aspect of the electrochemical composite coatings in the nickel matrix 
using kaolin particles as dispersed phases 
 
By adding kaolin particles at a concentration of 
20 g/L, it has been found that layer thickness 
increases relative to pure nickel deposits which 
confirms the inclusion of dispersed phase particles 
into the metal matrix. As regards the morphology of 
the layer, there is a binary symmetry, both pyramidal 
and pseudo-pentagonal (Fig. 3). 
Following the EDS analysis performed on the 
P6 sample both on surface and punctually, it was 
found that the distribution of the dispersed phase in 
the deposited layer is relatively uniform (Fig. 4 and 
5). 
For the current density of 12 A/dm2, it was 
considered that the optimal deposition regime was 
that of the P7 sample (Dcrt = 12 A/dm2, v = 500 rpm, 
t = 60 minutes), the other regimes leading to less 
adherent and compact deposits. 
With higher current densities, the concentration 
of metal ions in the immediate vicinity of the crystals 
decreases a lot and the crystals tend to grow towards 
the edges of the sample where the concentration of 
these ions is higher. Dendritic or spongy structures 
are thus obtained. Fig. 6 shows the influence of 
current density and stirring velocity on the layer 
thickness of pure nickel coatings and on 
electrochemical composite coatings in the nickel 
matrix using dispersed kaolin particles. It can be seen 
that increasing the current density and the stirring 
speed, the thickness of the obtained layer increases, 
while the temperature and the deposition time remain 
constant. The resulting composite coatings feature 
higher thicknesses compared to pure nickel deposits. 
 
5 m 
5 m 
10 m 
10 m 
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
No. 1 - 2018, ISSN 1453-083X 
 
 
          
 
Fig. 3. SEM image of the deposited layer for sample P6 
 
Fig. 7 shows the influence of the current density 
and stirring velocity on the microdurity of pure nickel 
coatings and on electrochemical composite coatings 
in nickel matrix using dispersed kaolin particles. 
It can be seen that when increasing the density 
of the current and the rate of stirring, the 
microhardnessy of the obtained layer increases, the 
temperature and the deposition time being kept 
constant. This increase is due, on the one hand, to the 
increase in the stresses in the layer with the current 
density, and on the other hand to the better inclusion 
of the dispersed phase particles into the deposited 
layer. 
Following the accelerated corrosion test 
performed in saline mist, it has been found that 
composite coatings exhibit a better corrosion 
behaviour compared to the pure nickel coating, as 
shown in Fig. 8. The presence of kaolin particles in 
the nickel matrix, correlated with the deposition 
parameters (current density, stirring rate), led to 
increased corrosion resistance in saline mist, the best 
behaviour being with samples P2, P5, P6, P7 where a 
higher passivation of the deposited layers was found. 
 
 
 
 
4. Conclusions 
 
The following conclusions can be drawn from 
the experimental researches: 
❖ the nickel coatings obtained from variations 
in current density and stirring rate are homogeneous, 
crackles and have good adhesion to copper supports; 
the increase in the current density also increases the 
thickness of the obtained layer; 
❖ the electrochemical composite coatings in 
nickel matrix using dispersed kaolin particles are 
homogeneous and crackles; the increase in the current 
density leads to the formation of finer structures as a 
result of the multiplication of crystallization germs on 
the cathode; 
❖ when increasing both the  current density 
and the stirring speed, the thickness of the layer thus 
obtained increases from 0.05 mm for pure nickel 
coatings obtained at a current density of 6 A/dm2 and 
a stirring speed of 500 rpm at 0.12 mm for pure 
nickel coatings obtained at a current density of 12 
A/dm2 and 900 rpm, from 0.059 mm for ACE Ni - 
kaolin obtained at a current density of 6 A/dm2 and a 
stirring speed of 500 rpm to 0.135 mm for ACE Ni - 
kaolin obtained at a current density of 12 A/dm2 and 
900 rpm, the temperature and deposition time being 
constant; 
 
 
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
No. 1 - 2018, ISSN 1453-083X 
 
 
 
 
Fig. 4. Surface EDS analysis for sample P6 
 
 
 
 
 
 
 
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
No. 1 - 2018, ISSN 1453-083X 
 
 
 
 
Fig. 5. Punctual EDS analysis on the dispersed phase particle 
 
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
No. 1 - 2018, ISSN 1453-083X 
 
 
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
6 9 12
T
h
ic
k
n
e
s
s
, 
[m
m
]
Current density, [A/dm2]
500rpm-Ni 700rpm-Ni 900rpm-Ni 500rpm-Ni-caolin 700rpm-Ni-caolin 900rpm-Ni-caolin
 
 
Fig. 6. The influence of current density and stirring velocity on the layer thickness of pure nickel 
coatings and on electrochemical composite coatings in nickel matrix using kaolin particles as 
dispersed phase 
 
 
0
50
100
150
200
250
300
350
400
6 9 12
M
ic
ro
h
a
rd
n
e
s
s
, 
H
V
0
.0
5
, 
[d
a
N
/m
m
2
]
Current density, [A/dm2]
500rpm-Ni 700rpm-Ni 900rpm-Ni 500rpm-Ni-caolin 700rpm-Ni-caolin 900rpm-Ni-caolin
 
 
Fig. 7. The influence of current density and stirring velocity on the microdurity of pure nickel 
coatings and on electrochemical composite coatings in nickel matrix using kaolin particles as 
dispersed phase 
 
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
No. 1 - 2018, ISSN 1453-083X 
 
 
0
20
40
60
80
100
120
140
160
180
200
24 48 72 96
C
o
rr
o
s
io
n
 r
a
te
, 
[m
g
/m
2
h
]
Time, [h]
P1 P2 P3 P4 P5
 
 
Fig. 8. Corrosion behaviour of electrochemical composite coatings in nickel matrix using kaolin 
particles as dispersed phase 
 
❖ the electrochemical composite coatings in 
nickel matrix using dispersed kaolin particles exhibit 
higher microhardness  compared to pure nickel 
coatings; thus the microdurity increases from 104.4 
daN/mm2 for copper support at 240 - 290 daN/mm2 
for pure nickel coatings, to 264 - 375 daN/mm2 for 
ACE Ni - kaolin coatings obtained at different current 
densities and stirring velocities, temperature and 
deposition time being maintained constant; this 
increase is due, on the one hand, to the increase in the 
stresses in the layer with the current density, and on 
the other hand to the good incorporation of the 
disperse phase particles in the deposited layer and its 
hardening; 
❖  salt mist corrosion behaviour of 
electrochemical ACE Ni - kaolin was superior to pure 
nickel layers, due to the passivation during the test. 
 
References 
 
[1]. Yahia H. Ahmad, Adel M. A. Mohamed, Electrodeposition 
of Nanostructured Nickel-Ceramic Composite Coatings: A review, 
International Journal of Electrochemical Science., 9, 2014. 
[2]. Raul Novac, Materiale compozite cu proprietăţi speciale, Teză 
doctorat, Galaţi, 2011. 
[3]. Davies Nathan, Applications of Clay Sedimentation: 
Deposition of CIGS Photovoltaic Inks, December 2014, Institute of 
Mathematics and Physics Aberystwyth University. 
[4]. Pavlov A. I., Influenţa tratamentelor electrochimice a 
suprafeţelor (straturi nanocompozite în matrice de nichel) asupra 
rezistenţei la coroziune şi uzură, Teză de doctorat, Galaţi, 2012. 
[5]. Gül H., Kılıc F., Aslan S., Alp A., Akbulut H., 
Characteristics of electro-co-deposited Ni–Al2O3 nano-particle 
reinforced metal matrix composite (MMC) coatings, Wear, 267, p. 
976-990, 2009. 
[6]. Tushar Borkar, Electrodeposition of nickel composite 
coatings, Mumbai University India, 2007. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Studies and Researches on Obtaining Electrochemical Composite Coatings in Nickel - Ni / Kaolin Matrix

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Studies and Researches on Obtaining Electrochemical Composite Coatings in Nickel - Ni / Kaolin Matrix

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