Journal of Surface Engineered Materials and Advanced Technology, 2013, 3, 89-93
http://dx.doi.org/10.4236/jsemat.2013.31A013 Published Online February 2013 (http://www.scirp.org/journal/jsemat)
89
Assessment of the Erosive Wear Kinetics of Epoxy
Coatings Modified with Nanofillers
Danuta Kotnarowska*, Michał Przerwa
Department of Mechanical Engineering, University of Technology and Humanities, Radom, Poland.
Received October 20th, 2012; revised November 25th, 2012; accepted December 3rd, 2012
ABSTRACT
The paper presents results of investigation on the erosive wear kinetics of epoxy coatings modified with alumina or sil-
ica nanoparticles. Natural weathering caused a decrease of their erosive wear resistance. After a 3-year natural weather-
ing, highest erosive wear resistance showed the epoxy coating modified with alumina nanoparticles.
Keywords: Polymer Coating; Nanofillers; Erosive Wear Resistance; Natural Weathering
1. Introduction
During their service life, polymer coatings are exposed to
various environmental factors that deteriorate their pro-
tective and decorative functions. Among the exposure
factors that affect polymer coatings applied on technical
objects exposed to natural weathering conditions the fol-
lowing ones are most common: climatic factors (ultra-
violet radiation, heat, humidity), aggressive media and
erosive particles [1].
Erosion is the dominating wear process of polymer
protective coatings of agricultural, constructional and
mining equipment or facilities and occurs as a result of
erosive particle impacts typical for a given environment.
The erosive wear process occurs when hard particles
(mineral particles, sand, dust, soil lumps, hail etc.) im-
pact the surface of the object. Hard particles cause wear
of the surface which leads to material losses in the super-
ficial layer [2,3,4]. Erosive wear of polymer coatings
manifests itself in abrasion, peeling, scratching, losses of
their parts as well as deformation of the coating with
substrate—in the places where erosive particles impact
the coating. This is a complex process and its kinetics
depends on particles material kind, their geometrical pa-
rameters, shape, velocity and impact angle as well as on
the coefficient of friction between the coating and ero-
sive particle. Erosive wear intensity of coatings rises with
a synergetic action of heat strokes, ultraviolet radiation as
well as aggressive media. Environmental factors affect
elastic, frictional and strength properties of polymer
coatings determining their erosive wear resistance.
Ultraviolet radiation is the most dangerous climatic
factor that causes chemical and physical destruction of
polymer coatings [5,6] which, first of all, destroys super-
ficial layers generating silver cracks. Superficial silver
cracks can also propagate inside the coating. As the re-
sult of the action of ultraviolet radiation, an intensive
chemical and physical destruction of coating surfaces
occurs which, first of all, deteriorates coating decorative
properties [7]. UV radiation induces oxidation of coating
superficial layers what results in an increased brittleness.
This manifests itself in a loss of cohesion between bind-
ing resin and fillers and pigments. In the next stage, pig-
ment and filler particles are released from the coating
surface layers. This process is called chalking and causes
an increase of the surface roughness which, in turn,
causes gloss loss and colour fading deteriorating, ipso
facto, coating decorative properties. Moreover, micro-
roughness cavities create favourable environment for the
growth of microorganisms (such as viruses, bacteria and
mould fungi) leading to the coating degradation in result
of biological corrosion development, for instance in form
of etching pits in the coating structure. Pits generated in
coatings can develop and, in the final stage, they can
reach the substrate and due to this the coating loses its
decorative and protective properties. Deterioration of
decorative properties may also result from the action of
such aggressive media as: brine, marine breeze, acid
rains, exploitation fluids and bird droppings [8-11]. Ag-
gressive media induce also coating cracking and swelling
as well as generate pores [12,13] that deteriorate the pro-
tective effectiveness of the coating. Moreover, aggressive
media trapped beneath the coating, where they accumu-
late, may induce blistering processes, whereas, a direct
contact of aggressive media with the metal substrate
*Corresponding author.

Assessment of the Erosive Wear Kinetics of Epoxy Coatings Modified with Nanofillers
90
causes the development of corrosion processes. Corro-
sion products formed at the substrate surface reduce or
destroy the coating/metal bond what leads to the adhe-
sion loss [8,10,14].
The need to investigate kinetics of organic coating
erosive wear caused by hard particles impacting results
from the fact that the erosive wear process is not suffi-
ciently recognised. Additionally, in the studies on the
erosive wear kinetics of polymer coatings, the extent of
coating destruction induced by environmental factors
(aggresive media, ultraviolet radiation, mechanical stresses)
should also be taken into consideration because the ero-
sive wear intensity is conditioned by changeable envi-
ronmental conditions [15-17].
2. Method of Coating Sample Preparation
Three-layer epoxy coatings (Figure 1) were applied by
air-spraying on the steel substrate. The coating consisted
of two primer layers (2 and 3) and one unmodified (A) or
nanofiller-modified (B) surface layer.
The samples used in the investigation were made of
S235JR steel and were of dimensions 160 × 80 × 2 mm.
The surfaces of the samples were prepared by grit blast-
ing (in a special tumbler) with the use of small ceramic
bars. Before coating application the samples were de-
greased.
The epoxy paint was modified with alumina nanopar-
ticles (Al2O3) with the grain size of 20 nm or silica
nanoparticles with the size of 12 nm. The nanofiller con-
tent was 3.5% (by weight). The obtained coatings were
acclimatised for 10 days at the temperature of 20˚C and
the relative humidity of 65% ± 5% (PN-EN 23270:1993).
3. Investigation Methodology
The coating thickness was measured with the use of
Figure 1. Cross-section scheme of the investigated epoxy
coatings; (a) unmodified coating; (b) modified coating, 1—
steel substrate; 2—primer layer I (epoxide); 3—primer
layer II (epoxide); A—unmodified surface layer; B—nano-
fillermodified surface layer.
Mega-Check FE meter (according to the Polish standard
PN-EN ISO 2808:2000). The average thickness of the
three-layer coatings was equal to 120 μm, including the
surface layer with the thickness of 40 μm. The coating
hardnes was determined with the application of the
Buchholz method (according to the Polish standard PN-
EN ISO 2815:2004). For coating roughness measure-
ments the Hommel T500 tester was applied (according to
the Polish standards PN-87/M-04251, PN-ISO 8501-1:1996,
PN-ISO 8501-1:1998).
Methodology of the Erosive Wear
Resistance Evaluation
The resistance to erosive wear was evaluated using the
falling abrasive particles method which consists in sub-
jecting coatings to the action of abrasive material stream.
The investigation on the coating erosive wear was carried
out using the apparatus presented in Figure 2.
The resistance to erosive wear of polymer coatings was
evaluated applying the criterion S according to Equation
(1). It expresses a proportion of the total mass M of
erosive particles which erode the coating (exposing the
steel substrate surface of the ellipsoid shape with the
minor diameter d = 3.6 ± 0.1 mm) to the coating thickness
G:
M
SG  (1)

200
60
o
 22
 19
915
25

4
5
2
1
3
Figure 2. Apparatus for erosive wear of polymer coating
testing: 1—container for erosive material; 2—pipe trans-
porting erosive material; 3—optical microscope; 4—tilting
holder for fixing metallic test specimen with examined
coating; 5—container collecting erosive material after the
test.

Assessment of the Erosive Wear Kinetics of Epoxy Coatings Modified with Nanofillers 91
where: S—erosive wear resistance, [kg/μm]; M—mass of
erosive particles, [kg]; G—average coating thickness,
[μm]. Particles of granulated alundum 99A (according to
the Polish Standard PN-76/M-59111) of grain number 30
(according to PN-ISO 8486-2) were used as abrasive
material (Figure 3). Alundum grains were of the size
0.60 - 0.71 mm. The main constituent of erosive material
was aluminium oxide (minimum 99%). Other constitu-
ents were: silicon dioxide, iron oxide, calcium oxide and
sodium oxide.
A sample with tested coating was inclined by 45˚. The
tests were carried out at the temperature of 20˚C ± 2˚C
and the relative humidity of 65% ± 5%.
4. Investigation Results
The effect of weathering on the epoxy coating thickness
is presented in Figure 4. One may notice that coating
thickness decreased on average by 2% after a 3-year
ageing period. Swelling was observed only for unmodi-
fied coatings aged for 2 years. Addition of the nanofiller
favourably increased the coating structure tightness, what
prevented swelling of the nanofiller modified coatings.
Figure 3. Morphology of alundum particles.
1
2
3
y
2
= -x
2
- 0,6x + 135,9
R
2
= 0,9971
y
1
= -4,5x
3
+ 17,5x
2
- 17x + 180
R
2
= 1
y
3
= -2,2x + 184,8
R
2
= 0,8345
70
100
130
160
190
220
01234
Ageing time t, [y ears]
Thickness G, [

m]
1 - unm odified
2 - m odified with n anoa l um ina
3 - m odified with n anosil i ca
Figure 4. Thickness of epoxy coatings subjected to natural
weathering conditions for 3 years.
Hardness characteristics (Figure 5) of epoxy coatings
reveal an essential effect of the modification with alu-
mina or silica nanoparticles on an increase of the unaged
epoxy coating hardness. After a 3-year natural weather-
ing only the alumina modified coatings showed increased
hardness.
Results of the surface topography measurements of
epoxy coatings reveal an essential effect of a 3-year
natural weathering on an increase of the coating surface
roughness (Figures 6 and 7). The highest Ra and Rz pa-
rameters—over the whole weathering period—were ob-
served for coatings modified with nanosilica. Reasons of
the increased surface roughness can be accounted for a
tendency of silica nanoparticles to form globules. Such
explanation is confirmed by the increase of Ra and Rz
parameters by over 100%. Positive effect of modification
on the surface roughness decrease was stated for epoxy
coatings with the alumina modified surface layer.
The carried out investigation on epoxy coatings, after
3 year natural weathering, showed a decrease of the re-
sistance to alundum particles impacts. Moreover, the
results of erosive wear investigation proved that modify-
cation of epoxy coatings with nanosilica caused a slight
1
2
3
y
2
= 3x
2
- 9,4x + 92,1
R
2
= 0,99 46
y
1
= 2,33 33x
3
- 9,5x
2
+ 7,16 67x + 9 0
R
2
= 1
y
3
= 3,25 x
2
- 12,05x + 95,95
R
2
= 0, 9993
70
75
80
85
90
95
100
01234
Ageing time t, [years]
Hardness H
1 - unm o di fi ed
2 - m odi fi ed wi th n anoa l umi na
3 - modified with nanosilica
Figure 5. Hardness of epoxy coatings after 3-year natural
weathering.
1
2
3
y
2
= 0, 0 15x
2
+ 0,035x + 0,405
R
2
= 0,985
y
1
= -0, 01x
2
+ 0, 1 36x + 0, 371
R
2
= 0,9722
y
3
= 0,0 25x + 0, 9 65
R
2
= 0, 4 181
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
0123
Ageing time t, [years]
Roughness parameter R
a
, [

m]
4
1 - unmodi fied
2 - modi fied wi th na noal um i na
3 - modi fied wi th na nos il i ca
Figure 6. Effect of natural weathering on the Ra parameter
of epoxy coatings.

Assessment of the Erosive Wear Kinetics of Epoxy Coatings Modified with Nanofillers
92
decrease of their erosive wear resistance (by 5%). The
erosive wear resistance of epoxy coatings modified with
alumina was comparable with that of unmodified coat-
ings (Figure 8).
The surface layer of a nano-silica modified epoxy
coating showed the lowest erosive wear resistance (S)
after a 3-year natural weathering (Figure 9). Its erosive
wear resistance was over 12% lower compared to the
unmodified surface layer. The coating modified with
alumina nanoparticles showed the highest erosive wear
resistance—higher by 14% than the one of the unmodi-
fied coating.
Figures 10 and 11 present the effect of natural weather-
ing on a destruction of epoxy coating surface. As the result
of weathering, coating components lose cohesion with
epoxy resin and are released from coating surface layers.
5. Conclusions
In summary, it is concluded as follows:
1) Modification of the epoxy coating structure advan-
tageously affected the resistance to erosive particles ac-
tion of the coatings weathered naturally for 3 years only
1
2
3
y
2
= -0,1675x
2
+ 1, 2975x + 1,9525
R
2
= 0,9553
y
1
= 1,01x + 2,08
R
2
= 0,9986
y
3
= 0, 3075x
2
- 0,6115x + 5,673 5
R
2
= 0,9873
0,0
1,5
3,0
4,5
6,0
7,5
9,0
01234
Ageing time t, [y ears]
Roughness parameter Rz, [

m]
1 - unmodi fied
2 - modifie d with nanoal um i na
3 - modifie d with nanosi l i ca
Figure 7. Effect of natural weathering on the Rz parameter
of epoxy coatings.
1
2
3
y
3
= -0,115x
3
+ 0,5x
2
- 0,665x + 1, 0 2
R
2
= 1
y
2
= -0, 15 17x
3
+ 0,67x
2
- 0,8 983x + 1,21
R
2
= 1
y
1
= -0,14x
3
+ 0,615x
2
- 0,865x + 1,28
R
2
= 1
0,3
0,5
0,7
0,9
1,1
1,3
0123
Ageing time t, [y ears]
The resistance to erosive wear S, [ kg/
m]
4
1 - unm odi fi ed
2 - m odi fi ed wi th n anoal umi na
3 - m odi fi ed wi th n anosi lica
Figure 8. Erosive wear resistance of unmodified and modi-
fied epoxy coatings.
1
2
3
y
3
= 0,0275 x
2
- 0, 2955x + 0 ,9795
R
2
= 1
y
2
= 0, 075x
2
- 0,465x + 1, 1 65
R
2
= 0,9984
y
1
= 0, 045x
2
- 0,407x + 1, 2 03
R
2
= 0,9974
0, 3
0, 5
0, 7
0, 9
1, 1
1, 3
01234
Ageing time t, [y ears]
The resist an ce t o er os ive wear S, [k g/

m]
1 - unmodi fied
2 - modi fied with nanoa lum i na
3 - modi fied with nanosil ica
Figure 9. Erosive wear resistance of the surface layers of
unmodified and modified epoxy coatings.
Figure 10. Surface morphology of the epoxy coating modi-
fied with alumina nanoparticles: unaged (a) and subjected
to natural weathering conditions for 3 years (b).
Figure 11. Surface morphology of the epoxy coating modi-
fied with silica nanoparticles: unaged (a) and subjected to
natural weathering conditions for 3 years (b).
in the case of alumina nanoparticles application.
2) This is due to increased hardness of the nano-alu-
mina modified coatings and their lower surface rough-
ness compared to the unmodified coating.
3) Modification of epoxy coatings with nano-silica re-
sulted in lowering of the coating erosive wear resistance
during the whole 3-year weathering period. It resulted
from decreased hardness and increased surface roughness
of this type of coatings. Reasons of the increased surface
roughness of the nano-silica modified coatings can be
accounted for a tendency of silica nanoparticles to form
globules.
4) Moreover addition of a nanofiller, both silica and

Assessment of the Erosive Wear Kinetics of Epoxy Coatings Modified with Nanofillers
93
alumina, favourably increased the coating structure tight-
ness, what prevented humidity swelling of the nano-
filler modified coatings. Swelling was observed only in
the case of unmodified coatings after 2-year weathering
period.
5) Summarising, one can state that modification of
epoxy coatings with nanofillers resulted in an increased
in-service durability only in the case of modification with
alumina nanoparticles.
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