Original Article

High Performance Polymers

2014, Vol. 26(3) 255–264
Preparation of aluminum oxide-coated ª The Author(s) 2013
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DOI: 10.1177/0954008313509390
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of composite epoxy coatings research

He Yi1, Chunlin Chen2, Fei Zhong2 and Zhonghao Xu2

Abstract
Multiwalled carbon nanotubes (MWCNTs) were acidized to get MWCNTs-COOH; the aluminum oxide (Al2O3)-
coated MWCNTs hybrid material were prepared by sol–gel method and the result of cladding was verified using
x-ray diffraction and scanning electron microscopy. Silane-coupling agent (KH560) was used to modify the hybrid
materials. Composite coating with different concentrations of MWCNTs and Al2O3-coated MWCNTs was pre-
pared. The wear resistance of the composite coating was tested by wear tester. The impedance performance and
flexibility of Al2O3-coated MWCNTs/epoxy (2 wt%) and MWCNTs/epoxy (2 wt%, composite coating containing 2
wt% nanometer powder) were measured by the electrochemical workstation and mechanical testing equipment
(MTS). The results show that the corrosion resistance and wear resistance of the Al2O3-coated MWCNTs/epoxy
composite coating have some improvement compared with MWCNTs/epoxy, but a reduction in the flexibility of the
Al2O3-coated MWCNTs/epoxy (2 wt%) composite coating.

Keywords
Al2O3-coated MWCNTs, silane-coupling agent, composite coating, preparation, properties

Introduction composite material combines the good wear resistance

of Al2O3 and the excellent performance of MWCNTs.
In recent years, with the development of economy and
Al2O3-coated MWCNTs composite material reduces the
the petroleum industry in particular, increasingly com-
surface energy of the CNTs appropriately and improves
plex drill conditions of super deep wells and corrosion
the dispersion of nanoparticles. In this study, we have
gas wells began to appear. Given this complex drill con-
successfully prepared the Al2O3-coated MWCNTs
ditions, corrosion is becoming an increasingly serious
(Al2O3 clad MWCNTs) material through sol–gel method
issue. Therefore, anticorrosive coating has a very good
and prepared Al2O3-coated MWCNTs/epoxy composite
protection effect on drill pipes.1,2 Therefore, anticorro- coating, the MWCNTs/epoxy composite coating. Their
sion coating is frequently used in harsh environments
corrosion resistance and mechanical properties are tested
and also when exposed to different forms of friction and
through electrochemical workstation and MTS810 test-
wear.3 If the anticorrosion coating lacks mechanical
ing machine.
strength and wear resistance, the coating soon wears, the
material spalls, and the protection effect for steel is
lost,4 which is required to improve the drilling technol-
1
ogy and equipment level constantly. Carbon nanotubes State Key Lab of Oil and Gas Reservoir Geology and Exploitation,
Southwest Petroleum University, Chengdu City, Sichuan Province,
(CNTs) have good mechanical properties and corrosion People’s Republic of China
resistance, but the wear resistance is poor owing to lack 2
School of Chemistry and Chemical Engineering, Southwest Petroleum
of sufficient hardness. In addition, application of CNTs University, Chengdu City, Sichuan Province, People’s Republic of China
is limited because of aggregation.5 For this reason, a
majority of researchers modified the surface of the Corresponding author:
He Yi, State Key Laboratory of Oil and Gas Reservoir Geology and
CNTs, including grafting organic groups on the surface Exploitation, Southwest Petroleum University, Rd. 8, Xindu District,
and coating with inorganic material.6 The aluminum Chengdu City, Sichuan Province, 610500, People’s Republic of China.
oxide (Al2O3)-coated multiwalled CNTs (MWCNTs) Email: heyi007@163.com
256 High Performance Polymers 26(3)

Experimental with a mechanical stirrer after oscillation. Subsequently,

the solution was stirred for 1.5 h at 80 C and filtered in
Materials and equipments vacuum and dried.8,9
The following are the materials acquired: aluminum sul-
XRD test. The CNTs and clad material powder were tested
fate, MWCNTs (provided by Chengdu Organic Chemistry
by X’Pert Pro diffractometer. Copper K radiation source
limited company of Chinese Academy of Sciences), anhy-
with a voltage of 40 kV and a generator current of 40
drous ethanol (analytical reagent grade), sodium hydro-
mA was used. The scanning rate was 2 min1 and scan-
xide, deionized water, silane-coupling agent (KH560),
ning range was about 5–90 .
sulfuric acid, nitric acid, muffle furnace, numerically con-
trolled ultrasonic cleaners of KQ22OOD model, Fourier SEM experiment. CNTs, clad material powder, Al2O3-coated
transform infrared spectrometer (Beijing Rayleigh Analy- MWCNTs/epoxy, and MWCNTs/epoxy with composite
tical Instrument Company, Chaoyang, Beijing, China). coating were observed using JSM-7500F model SEM. The
Scanning electronic microscope (SEM; model JSM- information about the surface appearance of the CNTs, clad
7500F, JEOL, Tokyo, Japan), X’Pert Pro diffractometer material, and their dispersibility in resin were obtained.
(PANalytical, the Netherlands), electrochemical worksta-
tion (Shanghai Brilliance Instruments Limited Company, Infrared spectrum determination. A small quantity of modi-
Shanghai, China), BGD 750 blender (BIUGED Labora- fied CNTs, clad material, and unmodified powder were
tory Instruments Equipment Limited Company, Guangz- placed in a mortar and mixed with some potassium bromide
hou, China), BGD523 ABRASER wear tester, ML204/02 powder. After grinding sufficiently, the infrared absorption
electronic balance (Mettler Toledo Instruments Limited peaks through infrared spectrum were observed.
Company, Columbus, Ohio, USA), and YX-6050 model Electrochemical experiment. The base metal (P110) was pro-
inhaled sandblasting machine (Yu xin Machinery Equip- cessed into a steel sheet of 1  10  20 mm3, and the effec-
ment Limited Company, Sichuan, China). tive area of steel was about 4 cm2. The sandblasting
machine was used to pretreat the surface of steel to ensure
that the surface cleanliness was at Sa2.5 level (sandblasting
Experimental method level in conformity to Sweden SIS criterion). The epoxy
The preparation of clad material. MWCNTs were added to resin and curing agent, with blending ratio 3:1, were mixed
mixed acid (concentrated sulfuric acid:concentrated nitric with MWCNTs and Al2O3-coated MWCNTs of 2 wt%,
acid ¼ 3:1) and dispersed by ultrasonic cleaners for 20 min. respectively. The mixture seriflux was sprayed on the sur-
The mixture was poured into a three-necked flask and stir- face of steel after ultrasonic oscillation and mechanical stir-
red for 12 h at 40 C.7 After stirring, the well-acidized ring. The steel with coating was then kept for 30 min at
MWCNTs/mixture acid liquid was poured into a large room temperature. The coating was baked for 60 min at
amount of deionized water, washed to neutral by sodium 120 C, followed by 100 min at 220 C in an oven, and the
hydroxide solution, and dried at 80 C. The acidified samples (MWCNTs/epoxy(2 wt%) and Al2O3-coated
MWCNTs were again added to the deionized water and MWCNTs/epoxy(2 wt%)) were obtained. The coating cor-
oscillated for 15 min by numerically controlled ultrasonic rosion resistance property was tested by electrochemical
cleaners. The solution was then transferred into a three- workstation. The test frequency scope was 105–102 Hz.
necked flask and was violently stirred for 30 min. The Sine wave signal amplitude was 100–10 mV.10 The
prepared aluminum sulfate/deionized water solution was three-electrode system used comprised a saturated calomel
added slowly in the above-mentioned solution using drop- electrode as reference electrode, platinum electrode as aux-
ping funnel. The pH value of the solution was adjusted to iliary electrode, and the steel sheet with coating as the
8.5–9.5 with sodium hydroxide solution. The reaction was working electrode. Electrolyte solution was 3.5 wt% (mass
conducted at 40 C for 6 h, allowed to rest for 12 h, and fraction) sodium chloride solution; the water used in the
filtered and then the Al2O3-coated MWCNTs were dried experiments was distilled water.
at 80 C for 8 h. The clad material was calcined at 550 C
Abrasion resistance test. The well-epoxy resin/curing agent
in a muffle furnace.
seriflux with MWCNTs and Al2O3-coated MWCNTs of
The modification of CNTs and clad material. Well-acidized different concentrations were mixed, the mixture was dis-
MWCNTs and Al2O3-coated MWCNTs powder were persed with ultrasonic oscillation and mechanical stirring,
added into two beakers separately and deionized water/ and then seriflux was sprayed on the surface of circular
ethanol mixture was then poured into the two beakers. The glass. Cast films were cured in an oven for 120 min to
liquid mixture was dispersed for 30 min by numerically obtain a sample. The abrasion resistance of these coatings
controlled ultrasonic cleaners. The same proportion of was tested through BGD523 ABRASER wear tester. CS-
KH560 was added into the two beakers, respectively. The 17 rotor was employed in the test. The loading and the
solution was then transferred into two three-necked flasks number of rotations were 1 kg and 1000, respectively.
Yi et al. 257

Three-point bending test. The steel sheet was made as

shown in Figure 2. The sandblasting machine was used to
pretreat the surface of steel. The nanometer materials/
epoxy mixture that contained the nanometer powder 2 wt%
was sprayed on the steel. The crack size of these coatings
was observed after pressing the samples to the same radian.

Figure 1. Tensile test specimen.

Results and discussion
XRD analysis of cladding material
The characteristic diffraction peaks of CNTs at 2 ¼ 26.071

25
and 43.173 are shown in Figure 3.11 After being coated, the
200
diffraction peak of 43.173 still existed, but the diffraction
peak of 26.071 disappeared because of the shielding effect
Figure 2. Three-point bending specimen. of Al2O3. Simultaneously, the diffraction peak of 46.08 and
66.774 emerged, which is the characteristic diffraction
peak of Al2O3.12 According to the XRD pattern, the char-
Al2O3-coated MWCNTS acteristic diffraction peaks of CNTs still existed; therefore,
MWCNTS the cladding process did not damage the structure of CNTs.
Al2O3
In addition, the characteristic diffraction peak of alumina
shows that Al2O3s existed on the surface of CNTs.
37.092
46.085 66.774
SEM analysis of cladding material
43.382
26.309 Figure 4(a), (c), and (e) shows MWCNTs electron micro-
scopy images, which are magnified 20,000, 50,000, and
43.173
100,000 times, respectively, and Figure 4(b), (d), and (f) are
36.633 45.898 66.978 cladding material electron microscopy images, which are
magnified 20,000, 50,000, and 100,000 times. According
to the picture, the CNTs are perfect tubular structures before
0 30 60 being coated; the high-surface energy makes these tubular
2θ (deg) structures mutually tangle together because they were not
modified. The cladding material presents ‘‘honeycomb’’
Figure 3. X-Ray diffraction spectra of cladding material. structure after being coated. In general, the cladding material
still maintains tubular structure, which was not destroyed in
Friction pit was obtained through the friction between sheet the cladding process. A layer of material appeared on the
and coatings, and loss mass of coatings were weighed. surface of CNTs after being coated. In addition, the reunion
of powders reduced a lot, owing to the coating with a layer of
inorganic materials that can reduce the surface energy. The
Flexibility of coating measurement SEM shows that we have successfully coated a layer of
Flattening test. The MWCNTs/epoxy and Al2O3-coated Al2O3 films on the surface of CNTs through the sol–gel
MWCNTs/epoxy mixture of 2 wt% and pure epoxy was method.
sprayed on the steels that had the same radian. The coat-
ings were obtained after drying and solidification, and Infrared analysis
the crack size of these coatings was observed in onetime
Figure 5(a) to (d) shows the infrared spectra of Al2O3-
pressing test, which was tested using MTS810 test
coated MWCNTs/KH560, Al2O3-coated MWCNTs,
machine.
MWCNTs/KH560, and MWCNTs, respectively. All of
Tensile test. The steel sheet was processed as shown in them have absorption peaks around 1630 cm1 because
Figure 1. The sandblasting machine was applied for pre- acidification generates carboxyl group on the surface of
treating the surface of steel to make the surface cleanliness CNTs. The absorption peak of 570–800 cm1 is the charac-
reach Sa2.5 level. The MWCNTs/epoxy (2 wt%) and teristic peak of Al2O3.13 Figure 5(e) and (f) stand for
Al2O3-coated MWCNTs/epoxy (2 wt%), and pure epoxy enlarged view of Al2O3-coated MWCNTs/KH560 and
were evenly sprayed on the steel, stretching these coating Al2O3-coated MWCNTs at 2800 and 3000 cm1, respec-
up to yield. tively. The characteristic peak of KH560 emerged at
258 High Performance Polymers 26(3)

Figure 4. Cladding material SEM images. (a, c, and e) Images of MWCNTs magnified 20,000, 50,000, and 100,000 times, respectively; (b,
d, and f) Images of cladding material magnified 20,000, 50,000, and 100,000 times, respectively. MWCNTs: multiwalled carbon nano-
tubes; SEM: scanning electron microscopy.

a Al2O3-coated MWCNTS/KH560 Al2O3-coated MWCNTS/KH560

b Al2O3-coated MWCNTS
c MWCNTS/KH560
(a) d MWCNTS 2856.05957

2921.62744 2827.13257 1396.21008 (e) 2921.62744

1633.4115
786.81451 584.32544
(b)
3200 3100 3000 2900 2800 2700 2600 2500
1646.91077 Wave number (cm–1)
790.67145
611.32397
Al2O3-coated MWCNTS
(c)
1625.69763
(f)
2927.41284 2846.41724
(d)
1639.1969

3000 2900 2800

4500 4000 3500 3000 2500 2000 1500 1000 500
Wave number (cm–1)
Wave number (cm–1)

Figure 5. Infrared spectrogram of composite.

2925.4843 and 2846.4172 from Figure 5(e) and (c).14 How- EIS analysis of composite coating
ever, Figure 5(f) and (d) do not show these two character-
Figure 6 stands for the impedance spectra of Al2O3-coated
istic peaks. Therefore, the nanometer powders were
MWCNTs/epoxy(2 wt%), MWCNTs/epoxy(2 wt%), and the
modified with KH560 successfully.
pure epoxy after soaking for 2 h. According to the picture,
Yi et al. 259

Al2O3-coated MWCNTS/epoxy Al2O3-coated MWCNTS/epoxy

MWCNTs/epoxy MWCNTs/epoxy
Epoxy Epoxy
10000
3000

8000 2500
Zim (Ω cm2)

2000

Zim (Ω cm2)
6000

1500
4000
1000
2000
500

0 0

–5000 0 5000 10000 15000 20000 25000 30000 35000 0 2000 4000 6000 8000 10000 12000 14000

Zre (Ω cm2) Zre (Ω cm )

2

Figure 6. Impedance spectra of coatings after soaking for 2 h. Figure 8. Impedance spectra of coatings after soaking for 48 h.

Al2O3-coated MWCNTS/epoxy Al2O3-coated MWCNTS/epoxy

MWCNTs/epoxy MWCNTs/epoxy
Epoxy 2000 Epoxy
6000 1800
1600
5000
1400
4000 1200
Zim (Ω cm2)

Zim (Ω cm2)

1000
3000
800
2000 600
400
1000
200
0 0
–200
0 5000 10000 15000 20000 25000
0 1000 2000 3000 4000 5000
Zre (Ω cm )2
Zre (Ω cm ) 2

Figure 7. Impedance spectra of coatings after soaking for 24 h. Figure 9. Impedance spectra of coatings after soaking for 96 h.

the radius of impedance arc of Al2O3-coated MWCNTs/ However, the Warburg impedance arc did not emerge in the
epoxy (2 wt%) is larger than MWCNTs/epoxy (2 wt%) and Al2O3-coated MWCNTs/epoxy composite coating and
the pure epoxy. The size of radius delegates the size of MWCNTs/epoxy composite coating. Therefore, they can
impedance. Therefore, the impedance of Al2O3-coated play a protective role to metal substrate.
MWCNTs/epoxy (2 wt%) composite coating is the largest. Figure 9 indicates the impedance spectra of 3 kinds of
Figure 7 shows the impedance spectra of 3 kinds of coatings coatings after soaking for 96 h. We can see that the impe-
after soaking for 24 h. The impedance of the 3 coatings is much dance of the pure epoxy already is smaller than 250  cm2,
smaller than at 2 h because the electrolyte solution penetrates which indicates that the pure epoxy has completely failed.
the coating with the increase in immersion time. The impe- For the MWCNTs/epoxy composite coating, the Warburg
dance of 3 kinds of coating shows the same change trend both impedance arc already starts to emerge and appear two
at 2 h and at 24 h. The impedance of Al2O3-coated MWCNTs/ times constant, which shows that electrolyte solution has
epoxy(2 wt%) composite coating is still the largest. penetrated into the coating and has arrived at the interface
Figure 8 shows the impedance spectra of 3 kinds of coat- of coating/metal base. However, Al2O3-coated MWCNTs/
ings after soaking for 48 h. The impedance of three kinds of epoxy composite coating still does not have these features.
coating reduced a lot. Warburg impedance arc and two time It illustrates that Al2O3-coated MWCNTs/epoxy composite
constant of the pure epoxy coating began to emerge. coating has a better protection.
260 High Performance Polymers 26(3)

Cc Cc
Rs Rs Cdl

Rc Rpo
Rt

(a) (b)

Figure10. The equivalent circuit.

Table 1. Loss of composite coating containing different percentage of MWCNTs.

Percentage (%)
Weight loss per milligram 5% 3% 2% 1% 0.7% 0%

55.7891 55.5155 56.8872 59.7704 57.0877 57.3174

55.7756 55.5052 56.8796 59.7623 57.0784 57.3067
Weight loss for the first time per milligram 13.5 10.3 7.6 8.1 9.3 10.7
55.7636 55.4951 56.8722 59.7544 57.0687 57.2965
Weight loss for the second time per milligram 12 10.1 7.4 7.9 9.7 10.2
55.7511 55.4846 56.8638 59.7457 57.0581 57.2849
Weight loss for the third time per milligram 12.5 10.48 8.4 8.7 10.6 10.8
Average loss per milligram 12.67 10.29 7.8 8.23 9.87 10.56
MWCNTs: multiwalled carbon nanotubes.

14
a
composite coating is equivalent to an isolation layer that
b has great resistance and small capacitance. When electro-
13 c lytes solution has not yet penetrated into the interface of
d coating and metal substrate, the capacitance of coating
12
Weight loss (mg)

increased and its resistance decreased with extending of

11 immersion time. Figure 8 shows that Warburg impedance
arc for MWCNTs/epoxy composite coating begins to
10 appear after soaking for 96 h. The equivalent circuit dia-
gram of impedance spectrum fits with Figure 10(b); Rpo
9
is microporous resistance of coating surface, Cdl is double
8
layer capacitance of interface blister part, and Rp is the
polarization resistance of the reaction of metal corrosion.16
7
0 1 2 3 4 5
Percentage (%) Abrasion resistance analysis
Figure 11. (a) Represents first wear value. (b) Represents the Table 1 shows the wear data of composite coatings contain-
second wear value. (c) Represents the third wear value, and (d) ing different percentages of MWCNTs. According to the
represents the average value of three times after grinding. table, the same trend emerged after repeating the experi-
ment thrice; all the results show that the coating has the best
With the extension of immersion time, the impedance of abrasion resistance at 2 wt%. The CNTs have better com-
the sample reduced gradually. At the beginning of the patibility with epoxy resin when the addition is 2 wt%.
immersion, the speed of electrolyte solution passing MWCNTs play the role of the physical junction.17 In addi-
through coating from the pore of the epoxy coating is far tion, the enormous draw ratio enables it to better adsorb
less than the speed of production of the corrosion products epoxy resin and then strengthen the cohesive action
at the interface between coating and metal substrate, this between metal substrate and epoxy. As a result, it advanta-
stage is called diffusion control corrosion reaction pro- geously disperses the stress and increases its wear resis-
cess.15 Figure 10(a) shows the equivalent circuit diagram tance.18 We can see the result intuitively from Figure 11.
of the impedance spectrum with ZSimpWin fitted; Rs Table 2 shows the wear data of composite coating that
denotes solution resistance, Cc denotes the capacitance of contains different percentages of Al2O3-coated MWCNTs.
coating, and Rc denotes the resistance of coating. The These results show that the coating has the best abrasion
Yi et al. 261

Table 2. Loss of composite coating containing different percentage of Al2O3-MWCNTs.

Percentage (%)
Weight loss per milligram 5% 3% 2% 1% 0.7% 0%

51.1365 55.8403 53.8330 53.7859 54.8133 57.3174

51.1274 55.8354 53.8289 53.7814 54.8075 57.3067
Weight loss for the first time per milligram 9.1 4.9 4.1 4.5 5.8 10.7
51.1192 55.8299 53.8250 53.7814 54.8008 57.2965
Weight loss for the second time per milligram 8.2 5.5 3.9 4.8 6.7 10.2
51.1106 55.8246 53.8207 53.7766 54.7945 57.2849
Weight loss for the third time per milligram 8.6 5.3 4.3 5 6.3 10.8
Average loss per milligram 8.63 5.23 4.1 4.76 6.26 10.56

MWCNTs: multiwalled carbon nanotubes; Al2O3: aluminum oxide.

a 13 a
b b
11 12
c
d 11
10

Weight loss (mg)

10
9
Weight loss (mg)

9
8
8
7 7
6 6

5 5
4
4
0 1 2 3 4 5
3
Percentage (%)
0 1 2 3 4 5
Percentage (%) Figure 13. (a) Represents the average wearing capacity of
MWCNTs/epoxy. (b) Represents the average wearing capacity of
Figure 12. (a) Represents first wear value. (b) Represents the Al2O3-coated MWCNTs/epoxy. MWCNTs: multiwalled carbon
second wear value. (c) Represents the third wear value, and (d) nanotubes; Al2O3: aluminum oxide.
represents the average value of three times after grinding.

respectively. Figure 14(d) to (f) shows pictures magnified

resistance at 2 wt% and has the same trend after repeating
500 times through metallographic microscope after press-
the experiment thrice (Figure 12).
ing (flat to rolling direction distance is 14.00 mm). The fig-
In Figure 13, ‘‘a’’ denotes the average attrition value of
ure shows that the crack in the pure epoxy is the biggest
MWCNTs/epoxy composite coating that contains different
among the three kinds of coatings; therefore, the flexibility
concentrations of MWCNTs and ‘‘b’’ denotes the average
of the pure epoxy without any padding is the worst. The
attrition value of Al2O3-coated MWCNTs/epoxy coating
crack in composite coating of Al2O3-coated-MWCNTs/
with different concentrations of cladding materials after
epoxy (2 wt%) is bigger than in MWCNTs/epoxy (2 wt%),
wearing thrice. According to the figure, there is significant
which illustrates that the flexibility of coating reduced after
improvement in the abrasion resistance of Al2O3-coated
being coated with a layer of Al2O3. Therefore, the flexibil-
MWCNTs/epoxy composite coating compared with the
ity of MWCNTs/epoxy (2 wt%) is the best.
MWCNTs/epoxy composite coating. The reason is that the
reunion of nanoparticles has reduced and the hardness of
Tensile test. The samples were stretched through the MTS810
coating has increased after being coated, resulting in the
testing machine. Tensile length of these samples is 1.5 mm;
increase in its abrasion resistance.
the results of experiment are shown in Figure 15. Figure
15(a) to (c) shows composite coating of the MWCNTs/
epoxy (2 wt%), Al2O3-coated-MWCNTs/epoxy (2 wt%),
The flexibility of composite coating test and epoxy before stretching, respectively. Figure 15(d) to
Flattening test. Figure14(a) to (c) represent pictures of com- (f) shows pictures magnified 500 times through metallo-
posite coating of MWCNTs/epoxy(2 wt%), Al2O3-coated graphic microscope after stretching. According to the figure,
MWCNTs/epoxy (2 wt%), and epoxy before pressing, all these coatings do not appear exfoliated after stretching;
262 High Performance Polymers 26(3)

Figure 14. Samples of pressing test. (a, b, and c) Pictures of composite coating of MWCNTs/epoxy(2 wt%), Al2O3-coated MWCNTs/
epoxy (2 wt%) and epoxy before pressing, respectively. (d, e, and f) Pictures magnified 500 times through metallographic microscope
after pressing. MWCNTs: multiwalled carbon nanotubes; Al2O3: aluminum oxide.

Figure 15. Tensile test specimen. (a, b, and c) Pictures of composite coating of MWCNTs/epoxy(2 wt%), Al2O3-coated MWCNTs/
epoxy (2 wt%) and epoxy before stretching, respectively. (d, e, and f) Pictures magnified 500 times through metallographic microscope
after stretching. MWCNTs: multiwalled carbon nanotubes; Al2O3: aluminum oxide.

Figure 15(d) to (f) shows that the crack in the pure epoxy is Three-point bending test. Figure 16 shows the results of the
larger than in the composite coating. The crack in the Al2O3- bending experiment (all samples were bent from 180 to
coated MWCNTs/epoxy (2 wt%) composite coating is larger 165 ). Figure 16(a) to (c) shows pictures of composite coat-
than in MWCNTs/epoxy (2 wt%). A layer of Al2O3 coating ing of MWCNTs/epoxy (2 wt%), Al2O3-coated-MWCNTs/
has a negative effect on the tensile property of composite epoxy (2 wt%), and epoxy after bending, respectively.
coating. In addition, nanometer material can enhance the Figure 16(d) to (f) shows pictures magnified 500 times
tensile property of the coating. through metallographic microscope. Obviously, the crack
Yi et al. 263

Figure 16. Three-point bending test. (a, b, and c) Pictures of composite coating of MWCNTs/epoxy(2 wt%), Al2O3-coated MWCNTs/
epoxy (2 wt%) and epoxy before bending, respectively. (d, e, and f) Pictures magnified 500 times through metallographic microscope.
MWCNTs: multiwalled carbon nanotubes; Al2O3: aluminum oxide.

Figure 17. SEM image of composite coating. (a, b, c, and d) Pictures of Al2O3-coated MWCNTs/epoxy (2 wt%) and MWCNTs/epoxy
(2 wt%)composite coatings magnified 30,000 and 50,000 times. MWCNTs: multiwalled carbon nanotubes; SEM: scanning electron
microscopy.

in Figure 16(e) was slightly larger than that in Figure 16(d); The SEM analysis of composite coating
however, the crack in Figure 16(f) was much larger than
Figure 17(a) and (c) are electron microscopic images of
that in Figure 16(e) and (d). It shows that coating a layer
Al2O3-coated MWCNTs/epoxy (2 wt%) and MWCNTs/
of Al2O3 film has weakened the bending property of com-
epoxy (2 wt%) composite coating magnified 30,000 times.
posite coating.
Figure 17(b) and (d) show the two composite coatings
264 High Performance Polymers 26(3)

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This work was sponsored by State Key Lab of Oil and Gas Reser- tems. J Electrochim Acta 2005; 50: 3324–3325.
voir Geology and Exploitation (PLN0806) and Sichuan Provincial 17. Ozimina D, Madej M and Kadon0 ski T. The wear resistance
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