Homogeneous epoxy coatings containing ZrO2 nanoparticles were applied on Grade A naval steel substrates. The morphology of the coating was characterized by optical microscopy and scanning electron microscopy. The effect of nanoparticles on the corrosion resistance of the hybrid coating was investigated by potentiodynamic polarization method. ZrO2 (1 wt.%) doping increased the microhardness of coating up to 15%, from 12.5 (kgf/mm2) to 14.4 (kgf/mm2). The coated steel samples were electrochemically monitorized over the 30 days of immersion in 5 wt.% NaCl solution. As shown by the polarization resistance and corrosion rate, the nanoparticles have a beneficial role, significantly improving the corrosion resistance

Gina Genoveva ISTRATE

Simona BOICIUC

Tamara RADU

Viorel PANAITE

Viorica MUSAT

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 
N0. 2 – 2013, ISSN 1453 – 083X 
 
 
 
 
 
EFFECT OF ZrO2 NANOPARTICLES ON THE MECHANICAL AND 
ANTICORROSION PROPERTIES OF EPOXY COATING 
 
*Viorel PANAITE1,2, Viorica MUSAT1, Simona BOICIUC1,  
Gina Genoveva ISTRATE1 and Tamara RADU1  
1Centre of Nanostructures and Functional Materials,  Faculty of Materials and Environment Engineering, 
”Dunărea de Jos” University of Galati, 47, Domneasca Street, RO-800008, Galati, Romania,  
2Bureau Veritas Romania Controle International 165b, Galati, Brailei Street, RO-800310, Galati, Romania 
*Corresponding author 
email: panaite_viorel@yahoo.com 
 
ABSTRACT 
 
Homogeneous epoxy coatings containing ZrO2 nanoparticles were applied on 
Grade A naval steel substrates. The morphology of the coating was characterized 
by optical microscopy and scanning electron microscopy. The effect of 
nanoparticles on the corrosion resistance of the hybrid coating was investigated by 
potentiodynamic polarization method. ZrO2 (1wt. %) doping increased the 
microhardness of coating up to 15%, from 12.5 (kgf/mm2) to 14.4 (kgf/mm2). The 
coated steel samples were electrochemically monitorized over the 30 days of 
immersion in 5 wt. % NaCl solution. As shown by the polarization resistance and 
corrosion rate, the nanoparticles have a beneficial role, significantly improving the 
corrosion resistance.  
 
KEYWORDS: nanoparticle, epoxy coating, Tafel curves, corrosion 
parameters 
 
1. Introduction 
 
Epoxy coatings have been widely used as a 
material to protect the metallic structures [1-3] and 
represent one of the most used coating systems in 
naval field. The protective coatings for marine steel 
structures work in very demanding conditions. Epoxy 
coating is suitable for these multiple requirements, 
because of its excellent chemical resistance, good 
electrical insulating properties and strong adhesion to 
steel substrates, but often is susceptible to damage by 
surface abrasion and wear [4, 5] and also is poorly 
resistant to the propagation of cracks [6].  
Usually, epoxy coatings reduce the corrosion of 
a metallic substrate subject to an electrolyte. It is 
acting as a physical barrier layer against the ingress of 
a deleterious species and represent a reservoir for 
corrosion inhibitors. The barrier features of epoxy 
coatings can be enhanced by the incorporation of 
nanosized inorganic filler particles dispersed within 
the epoxy matrix, to form an epoxy nanocomposite.  
Thereby, the following benefits can be obtained: 
 Improving the integrity and durability of 
coatings by dispersion of fine particles in the cavities 
of epoxy matrix [7-9] which cause crack bridging 
[10]; 
 Preventing epoxy disaggregation during 
curing, resulting in a more homogeneous coating, due 
to tendency of nanoparticles to occupy small hole 
defects formed from local shrinkage during curing of 
the epoxy resin and act as a bridge, interconnecting 
more molecules; 
 Offering significant barrier properties for 
corrosion protection, by reducing the total free 
volume and increasing cross-linking density [11, 12]. 
In this work it is discussed the influence of ZrO2 
nanoparticles on the surface morphology, 
microhardness and anticorrosion parameters of epoxy 
coatings. A better understanding of the mechanisms 
through which nanoparticles interact with epoxy 
matrix is very important to offer subsequent 
guidelines in design of epoxy coatings with high 
performances in corrosion protection of steel. 
 
2. Experimental details 
 
2.1. Materials 
The epoxy resin, the hardener and the solvent 
used for coating deposition, commercially known as 
DER 353, I 3100 and D 309 respectively, were 
obtained from S.C. “Policolor” S.A. (Bucharest). 
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ZrO2 nanoparticles with diameter below 100nm, were 
purchased from Sigma Aldrich (Steinheim, 
Germany). Sodium chloride (NaCl) used for 
corrosion test was purchased from S.C. Silal Trading 
S.R.L. (Bucharest). As substrate it was used rectangle 
steel samples (50x20mm) of grade S235JR+AR 
according to EN 10025-2004; the steel substrates 
have the following chemical composition: 0.12% C, 
0.48% Mn, 0.015% Si, 0.013% P, 0.006% S, 0.039% 
Al, 0.016% Cu, 0.029% Cr, 0.024% Ni, 0.001% V, 
0.003% Mo, 0.001% Ti, 0.001% Nb, Fe in rest. The 
composition and mechanical properties are similar to 
those of naval steel grade A.  
 
2.2. Deposition of coatings 
Steel substrates were initially cleaned with 
acetone, sand-blasted to the grade “Sa 2½” and 
cleaned by immersion in acetone. To remove the 
microparticles remained on the surface after sand-
blasted, the substrates were sonicated for 10min. in 
acetone. Two types of coatings were prepared: epoxy 
and epoxy modified with ZrO2 nanoparticles. The 
weight ratio of the epoxy resin to the hardener was 
2:1. Before mixing, both resin and its hardener were 
diluted by solvent with a 1:1 weight ratio [13]. After 
that, the two solutions were stirred (1400rpm) using a 
Heidolph MR Hei-Tech magnetic stirrer, mixed and 
sonicated 10min. using a bath. For nanocomposite 
coating, at this resulted solution were added ZrO2 
nanoparticles, (1%) of the total weight of resin and 
hardener. The steel substrates were dipped into the 
obtained mixture, using a home-made dip-coater, at 
different withdrawn speed of 2.5, 5 and 10cm/min, 
respectively. After each layer deposited, the samples 
were kept at room temperature for 30min. and placed 
in an oven (Model FN 055 Nüve) at 90ºC for 30min. 
Finally, the samples were kept at room temperature 
for 30min.  
The following groups of samples were obtained: 
epoxy coating (six layers) and ZrO2 modified epoxy 
coatings (two layers noted with I and six layers noted 
with II) (Table 1). All the coated samples were kept at 
room temperatures for 14 days, to allow full curing 
for the subsequent mechanical and anticorrosion tests. 
 
2.3. Characterization of coatings 
The Thickness of the Dried Film (DFT) was 
measured by a nondestructive echo-sound test, using 
a 345 type Elcometer. The DFT values are presented 
in Table 1. The surface morphology and the cross-
section for the nanocomposite sample covered by six 
layers at withdrawn speed of 10 cm/min, were 
analyzed by Scanning Electron Microscopy (SEM) 
(model Zeiss EVO MA 15). Microhardness 
measurements were realized for the samples covered 
by six layers, using a specific system (model PMT–
3), according to EN ISO 6507/1 – 2002 [14] and 
equation (1),  
HVF=1.8544*F/d2 [kgf/mm2]                         (1) 
where F is strength test and d is diagonal of 
square trace remained after test.  
The anticorrosive performance of 
nanocomposite coatings was investigated by 
potentiodynamic weak polarization method. The 
samples were kept immersed in corrosive solution 
(5wt.% aqueous NaCl solution) over the 30 days and 
the measurements of corrosion parameters were 
carried out periodically using Voltalab PGP 201 
Radiometer Analytical equipment, with three 
electrodes: the epoxy coated steel sample served as 
the working electrode, while the counter electrode 
and the reference electrode used were a platinum grid 
and a saturated calomel - Ag/AgCl (Sat. KCl), 
respectively. A special cell ensures the reproducibility 
of the experimental parameters, especially the 
distances between electrodes and the free sample 
surface (0.5024cm2) in contact with the corrosive 
solution. The steel was polarized around its corrosion 
potential, in general in the potential range of -
1000mV÷ +200mV by a direct current (DC) signal, at 
a scan rate of 0.2mV/s. The results were processed 
with the application VoltaMaster software, version 4, 
using the following experimental parameters: 
diameter of the free surface of the sample (8mm); 
solution expose surface aria (50.24mm2); steel sample 
density (7.8kg/dm3) and iron valence (2). 
 
3. Results and discussion 
 
3.1. Effect of nanoparticles on the 
morphology of epoxy coating 
Optical top-view images of the investigated 
samples are shown in Figure 1, which indicates that 
cured epoxy coatings have a relatively homogeneous 
morphology, the ZrO2 modified epoxy coatings are 
denser and apparently showed no sign of 
nanoparticles agglomeration. The average thickness 
of the epoxy coatings for the sample studied, 
estimated from its cross-sectional view (as shown in 
Fig. 2a) is in accordance with the thickness of the 
coating measured by nondestructive echo-sound test. 
Six layers epoxy coating has the same range DFT 
with two layers ZrO2 modified epoxy coatings (I). 
These coatings are much thinner than the six layers 
ZrO2 modified epoxy coatings (II) (Table 1), which 
are very homogeneous in value. As it can be seen in 
Figure 2a, the surface of coating has small roughness, 
the coating shows a good compliance and adherence 
to the substrate, is very compact, without boundaries 
between the deposited layers.  
The sample studied has some agglomeration of 
zirconia nanoparticles, revealed by cross section view 
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(see zone A of 24.38µm2) (Fig. 2a) and chemical 
analysis (Fig. 2b). 
 
3.2. Effect of nanoparticles on the 
mechanical properties – microhardness 
As the indentation depth in microhardness 
measurements done on PMT–3 system is around 3µm 
and the coating thickness is above 25µm, the 
contribution of steel substrate to the final results of 
microhardness is negligible. In this work we presume 
that all the coatings have identical mechanical 
properties over the entire thickness and the results of 
microhardness so measured are the representative 
value of the whole coatings. 
 
    
 
Fig. 1. Optical micrographs of epoxy coatings obtained by six layers,  
at withdrawn speed of 10cm/min: a) plain epoxy; b) nanocomposite coatings  
 
    
 
Fig. 2. SEM images of nanocomposite coatings obtained by six layers, at withdrawn speed of  
10cm/min: a) cross sectional view, indicating a thickness of 82µm; b) chemical analysis specific 
for region A 
 
Table 1. DFT of the samples at different 
withdrawn speed 
 
Type of 
coating 
No. of 
layers 
Withdrawn 
speed 
(cm/min) 
DFT  
 
(µm) 
2.5 32±10 
5 50±10 Epoxy 6 
10 70±15 
2.5 35±5 
5 45±5 
ZrO2-Epoxy 
nanocomposite 
(type I) 
2 
10 50±8 
2.5 80±12 
5 95±10 
ZrO2-Epoxy 
nanocomposite 
(type II) 
6 
10 112±18 
Figure 3 shows the values of microhardness 
calculated considering the average thickness of film 
coatings, for the samples covered by six layers, 
measured in two different stages: as prepared (a) and 
after salt spray test chamber (480 hours) (b). The 
incorporation into epoxy of small amount of ZrO2 
nanoparticles (1wt.%) have a beneficial role, 
improving the microhardness of coating, up to 15% 
for the homologous samples obtained for the 
withdrawn speed of 2.5cm/min and maintains the 
values of microhardness upper or sensitive to values 
equal in rest.  
This beneficial role is particularly relevant in 
time, when the coating has worked in demanding 
conditions (after salt spray test chamber).
a) 
b) A 
A 
Steel substrate
Coating 
a) b) 
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3.3. Effect of nanoparticles on the 
corrosion resistance of the coated steel 
The corrosion potential, corrosion current, 
polarization resistance and instantaneous rate were 
estimated from the measured potentiodynamic 
polarization curves of epoxy-coated steel.  
Fig. 4 shows the temporal evolution of 
instantaneous corrosion rate and polarization 
resistance (Rp) of steel samples coated at withdrawn 
speed of 2.5 cm/min, during the 30-day immersion in 
5wt.% NaCl solution. To conclude on the beneficial 
role of introducing nanoparticles into epoxy matrix, it 
is better to compare the temporal evolution of the 
corrosion parameters for plain epoxy with 
nanocomposite type I, the two coatings having DFT 
closer as values. 
 
12
12.5
13
13.5
14
14.5
20 30 40 50 60 70 80 90 100 110 120
Average thickness of coating (µm)
M
ic
ro
ha
rd
ne
ss
 (K
gf
/m
m
2 )
Epoxi Epoxi+ZrO2(II)
          
12
14
16
18
20
22
24
26
30 50 70 90 110 130
Average thickness of coating (µm)
M
ic
ro
ha
rd
ne
ss
 (K
gf
/m
m
2 )
epoxi epoxi+ZrO2(II)
 
 
Fig. 3. Microhardness values calculated considering the average thickness film, for plain epoxy and 
the ZrO2 modified epoxy coating (II) (six layers): a) as prepared; b) after salt spray corrosion test 
 
0.01
0.1
1
10
100
1000
10000
0 200 400 600 800 1000
Time in 5% NaCl solutions (hrs)
C
or
ro
si
on
 ra
te
 (µ
m
/y
ea
r)
Bare steel Epoxy Epoxy+ZrO2(I) Epoxy+ZrO2(II)
      
0.01
0.1
1
10
100
1000
10000
100000
0 200 400 600 800 1000
Time in 5% NaCl solutions (hrs)
Po
la
riz
at
io
n 
re
si
st
an
ce
 (k
Ω
cm
2 )
Bare steel Epoxy Epoxy+ZrO2(I) Epoxy+ZrO2(II)
  
 
Fig. 4. Temporal evolution of: corrosion rate - a); polarization resistance - b), for samples coated  
at withdrawn speed of 2.5cm/min, measured in 5wt% aqueous NaCl solution, at different  
times of immersion
In case of nanocomposite type II, the beneficial 
role could be the result both of the presence of ZrO2 
nanoparticles and the thickness obtained after six 
layers deposited. So, the incorporation into epoxy 
coating of small amount of ZrO2 nanoparticles 
(1wt.%) significantly reduced the corrosion rate of the 
epoxy-coated steel over the 30-day immersion in 
5wt.% NaCl solution, up to 80 times after 800 hours 
(Fig. 4a), and consequently leads to the adequate 
improving corrosion resistance of the epoxy-coated, 
up to 20 times (Fig. 4b). It can be noted that Rp for 
nanocomposite type II in comparison with similar 
value for nanocomposite  type I, is maintained higher 
by 3-27 times, while the corrosion rate at some 
moments of tests are better for nanocomposite type I. 
It is assumed that in the type I nanocomposite 
coatings, the nanoparticles were better dispersed, the 
two layers were thinner opposite to nanocomposite II, 
a) 
b) 
a) b) 
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in which some nanoparticles agglomeration were 
highlighted. For samples covered with six layers, 
each layer deposited leads to increasing the internal 
stress, the source for micro-cracks and pinholes [11, 
12], decreasing mechanical strength and corrosion 
resistance. 
 
Conclusions 
 
ZrO2 nanoparticles were successfully dispersed 
in epoxy based coatings at a concentration of 1%.  
The electrochemical monitoring of coated steel 
over the 30 days of immersion in 5wt.% NaCl 
solution suggested the beneficial role of nanoparticles 
in significantly improving the corrosion resistance of 
the coated steel. The epoxy coating modified with 
ZrO2 nanoparticles showed an important enhanced 
microhardness value.  
The hardness remains at good values for 
samples subjected to corrosion test for long time.  
For future research, it would be important to 
investigate ways to improve dispersion of the 
nanoparticles in the coating matrix, further effect of 
increasing ZrO2 nanoparticles content on the 
anticorrosive performance for epoxy coating; the 
potential application of the nanoparticles as reservoirs 
of corrosion inhibitors, for the storage and for 
releasing them in some conditions will be 
investigated.  
 
References  
 
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Effect of ZrO2 Nanoparticles on the Mechanical and Anticorrosion Properties of Epoxy Coating

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Effect of ZrO2 Nanoparticles on the Mechanical and Anticorrosion Properties of Epoxy Coating

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