MINISTRY OF EDUCATION
AND TRAINING

VIETNAM ACADEMY OF
SCIENCE AND TECHNOLOGY

GRADUATE UNIVERSITY OF SCIENCE AND
TECHNOLOGY
------------------------

NGUYEN THU TRANG

STUDY ON EFFECT OF Fe3O4 NANOPARTICLES IN
POLYMER NANOCOMPOSITE COATING FOR CORROSION
PROTECTION
Scientific Field: Polymer and Composite
Classification Code: 62.44.01.25
DISSERTATION SUMMARY

HANOI – 2019


The dissertation was completed at: Institute for Tropical Technology Vietnam Academy of Science and Technology and Faculty of Chemistry,
Hanoi University of Science - Vietnam National University.
Scientific Supervisors:
1. Assoc. Prof. Dr. Trinh Anh Truc
Institute for Tropical Technology - Vietnam Academy of Science and
Technology
2. Assoc. Prof. Dr. Nguyen Xuan Hoan
Dept. Physical Chemistry, Faculty of Chemistry, Hanoi University of
Science - Vietnam National University

With their own high chemical reactivity, metal and alloys easily are
corrosive in environment, especially in high temperature or electrolyte
solutions which is cause for having high socio-economic impacts, which
translate into substantial costs to the country. According to reports, around
1/3 of the mined metal all over the world cannot using anymore because of
corrosion. In addition to the direct damage that people can calculate,
corrosion of metals can also cause indirect damages such as reducing
machine durability and product quality, causing environmental pollution
and adverse effects to work safety. Therefore, the protection against metal
corrosion from the impact of the aggressive environment is becoming an
extremely pressing issue.
Protecting metal with organic coating has been widely used because
of its effectiveness, ease of processing and reasonable cost. Currently, the
new trend in the field of organic coatings is to find new inhibitors to replace
toxic chromates, creating an environmentally friendly coating, etc.
Nanotechnology has come to life and created tremendous breakthroughs.
Highly reactive pigments with nano dimensions when applied to organic
coatings to protect metal corrosion from concentrations of 2 - 3% show
breakthrough properties. In particular, iron oxides are considered as
pigments used in paint with all colors depending on the type of iron oxide
used, especially Fe3O4 magnetic iron oxide, corrosion protection ability so
far. The mechanism is still unclear.
For the above reasons, we propose the dissertation: “Study on effect
of Fe3O4 nanoparticles on polymer nanocomposite coating for
corrosion protection”

1


2. The main contents of the thesis

2.2. Synthesis iron oxides by hydrothermal method
 Synthesis α-Fe2O3 nanoparticles : FeCl3.6H2O was dissolved with
distilled water. Under stirring, a KOH solution was added to the
solution until the formation of a precipitate occurred. Hydrothermal
2


o

reaction was conducted at 180 C for 15 h. After reaction, the precipitate
was washed with distilled water and dried in a vacuum oven.
 Synthesis Fe3O4 nanoparticles: a mixture of FeCl 3.6H2O/FeSO4.7H2O
2+
3+
(molar ratio Fe /Fe = 1/1) was dissolved with distilled water. Under
stirring, a KOH solution was added to the solution until the formation of
a precipitate occurred. Hydrothermal reaction was conducted at
o

150 C for 7 h. After reaction, the precipitate was washed with distilled
2+
water to remove impurity ions (Cl , SO4 , K ) and dried in a
vacuum oven.
 Synthesis γ-Fe2O3 nanoparticles: Thermal
treatment process for
o
synthesized Fe3O4 nanoparticles at190 C for 2 hours
2.3. Modification Fe3O4 nanoparticles with organic compounds
 Modification Fe3O4 nanoparticles with silane: Silane was dissolved
with mixture solvent of etanol/distilled water (19/1 ratio). Fe 3O4 was

Evaluation method for physical and mechanical properties of coatings:
impact strength, pull-off strength, wet adherence.
Corrosion testing for coatings:
+ Electrochemical impedance spectroscopy
+ Salt spray test was used in order to evaluate the corrosion
protection of the samples.
CHAPTER 3. RESULTS AND DISSCUSIONS
3.1. CHARACTERISTICS AND PROPERTIES OF IRON OXIDES
3.1.1. Characterization of Fe3O4 nanoparticles
Figure 3.1. The XRD pattern of pure
magnetite obtained by hydrothermal method

Figure 3.1 showed the diffraction pattern
that allowed for unequivocal identification of
magnetite; using the ICSD (Inorganic Crystal
Structure Database) reference code 01-076-1849 for magnetite the
diffraction peaks were identified.

Figure 3.2. SEM micrographs of Fe3O4 obtained by hydrothermal method

Figure 3.2. showed SEM images of Fe3O4 particles obtained by the
hydrothermal treatment. The uniform particle morphology and size of
synthesized Fe3O4 were observed. The results confirm that nanoparticles
with average particle size around 50 - 70 nm were observed.

4


%T


Figure 3.5. showed SEM images of α-Fe2O3 particles obtained by the
hydrothermal method. The uniform particles in morphology and size of
synthesized Fe3O4 were observed. The results confirm that nanoparticles
had average particle size around 70 - 80 nm which was not good in
comparison with Fe3O4
5


–1

are related to Fe-O bonds in

nanoparticles and absorptions in 3420 cm

1625
565 476

and 476 cm

–1

3420

result showed that absorption at 565 cm

%T

FTIR
spectrum
of

the ICSD card no. 01-083-0112. No additional
diffraction peaks of any impurity were detected,
demonstrating the high purity of the synthesized samples.
(a)
Figure 3.8. Hysteresis loop of Fe3O4 and

100
80

γ- Fe2O3 particles. Image of magnetite and

(b)

M (emu/g)

40

60
20

maghemite nanoparticles were manipulated by

0

magnet (small image)

-20
-60

Fe3O4 (a)

Figure 3.10. FT-IR spectrum
of γ -Fe2O3 nanoparticles
The result showed that absorptions

3000
3000

2000
2000

-1 )
-1

SốSốsóng (cm)

1000
1000

–1

577

3436

623

1632

%TT(%)



Figure 3.11. Nyquist plots
for the epoxy coating

Figure 3.12. Nyquist plots
for the epoxy coating containing
3 % wt. α-Fe2O3 nanoparticles

Epoxy/α-Fe2O3

7


After 42 days of immersion, for the epoxy coating containing αFe2O3, the second cycle at low frequencies was determined. The result
showed that α-Fe2O3 play the role of a pigment which increase the barrier
property of coating. The EIS diagram of epoxy coating containing γ-Fe 2O3
are did not change the shape.
After 84 days immersion, impedance value of epoxy coating
containing Fe3O4 was higher than this value of another coatings because of
interacting of particles and oxides appearing at the steel/coating interface.
Figure 3.13. Nyquist plots for
the epoxy coating containing 3 % wt.
γ-Fe2O3

Figure 3.14. Nyquist plots for
the epoxy coating containing 3 %
wt. Fe3O4

10 10


5

0

20

40

60

80

100

Thời gian (ngày)

After 84 days of immersion, among coatings, the epoxy/Fe3O4 coating
had highest impedance modulus.
These result shown that the presence of iron oxides in epoxy matrix
significantly improved the barrier properties of the coating, especially Fe 3O4.
8


3.1.5. Mechanical properties of epoxy coating containing iron oxides
Table 3.1. Pull-off strengths and impact strengths for epoxy coating
and epoxy coating containing 3% wt. iron oxides
Samples
Pull-off strength (MPa)
Impact strength
(kg/cm)


(b)

(d)
(c)

0
3

1

2

6

10

3

4

24

epoxy coating containing 3% wt. Fe3O4 (b),

Thời gian (giờ)

α-Fe2O3 (c) and γ-Fe2O3 (d)

The increasing of wet adhesion of epoxy coating containing iron

groups, respectively. This result indicates that silanes have been
successfully grafted onto the surface of Fe3O4 nanoparticles.
DTA/TG analysis
The results showed on DTA curves improved that Fe3O4 nanoparticles
were modified by silanes (APTS, DMPS, TEOS).
Surface potentials of Fe3O4 nanoparticles and silanes modified
Fe3O4 nanoparticles

Figure 3.19. Surface potentials distribution of Fe3O4 and
Fe3O4 modified by silanes: APTS, DMPS và TEOS
The surface potential of Fe3O4 and modified Fe3O4 nanoparticles were
measured in a zeta potential analyzer (Figure 3.19). In the surface potentials
distribution plot of Fe3O4, there were 2 peaks focus on the value at -40 mV
and indicates the average value -21.8 mV. As a result of -OH groups in the
surface of Fe3O4 nanoparticles due to the following model: (surface)(–

OH )n . The average surface potential of modified Fe 3O4 with APTS,
DMPS and TEOS are -19.31 mV; -19.05 mV and -18.15 mV, respectively.
10


Therefore, -OH groups on the surface of Fe3O4 nanoparticles had a reaction
with –OH of silane molecules which lead to change in the surface potential
of nanoparticles. The observed zeta potential value shows the less stability
of the Fe3O4 nanoparticles.
Magnetic property of silane modified Fe3O4 nanoparticles
Figure 3.20. Hysteresis loops of
modified Fe3O4 particles
M (emu/g)


-10000 -500005000

35004500

10000

15000

magnetic particles obtained using a
magnetometer are show in Figure 3.20. The

H(Oe)

values of saturation magnetization the
Fe3O4 nanoparticles modified by APTS, DMPS and TEOS are 79.8 emu/g,
81.8 emu/g and 81.9 emu/g, respectively.
3.2.1.2. Characterization of corrosion protection of epoxy coating
containing silane modified magnetite nanoparticles.
EIS measurements were carried out to evaluate the corrosion
resistance of the carbon steel covered by epoxy coating containing 3% wt.
silane modified magnetite nanoparticles.
Figure 3.21. Nyquist plots
for the epoxy coating containing
3 % wt. Fe3O4/APTS

Fe3O4/APTS

After 1 hour immersion in 3 % NaCl solution, the EIS diagram of three
kinds of coatings presented one circle with very high value. After 24 days
immersion, for epoxy coating containing Fe 3O4/TEOS the second cycle at low

obtained with the epoxy coating containing Fe3O4/APTS and Fe3O4/TEOS.
109

Figure 3.24. Variation of Z1Hz values
with immersion time in NaCl 3% solution of
epoxy coating containing 3% wt. Fe3O4 and
silanes modified Fe3O4

|Z|1 Hz

108

107
106

Fe3O4
Fe3O4/APTS
Fe3O4/DMPS
Fe3O4/TEOS

105
0

20

40

60

80

γ-Fe2O3) and iron oxides occur at the surface of carbon steel prevent water
penetrated through the coating.
The pull-off strength of epoxy coating containing Fe 3O4/APTS and
Fe3O4/TEOS increased significantly in comparison with epoxy coating
containing Fe3O4. In wet condition, it observed that adhesive loss of the coating
with Fe3O4/APTS was smallest after 24 hours immersion in water. While this
loss of coating with Fe3O4/TEOS was equal to coating with Fe3O4/DMPS.

13


Table 3.2. Pull-off strengths and impact strengths for epoxy coating
containing Fe3O4 and Fe3O4 modified by silanes
Samples
Pull-off strengths impact strengths
(MPa)
(kg/cm)
5,9
7,1
6,0
7,8

Epoxy - Fe3O4
Epoxy - Fe3O4/ATS
Epoxy - Fe3O4/DMPS
Epoxy - Fe3O4/TEOS

>200

100

20

6

1

10

2
NF-ATS

NF

24

3
NF-DMPS

4

NF-TEOS

Thời gian (giờ)

0

1694

3000
2000


1099
1057

1386
1455
1427

1630
1629

IBA

1621

2921

3435

Fe3O4/IBA

(%
)

T (%)

Fe3O4

3433



-1

groups were observed at band 1385 cm -1630 cm . These peaks were also
found in the spectrum of pure IBA and BTSA. The comparison of these
spectras showed the presence of the IBA and BTSA molecules on the
surface of the Fe3O4 nanoparticles.
The DTA curves of Fe3O4/IBA và Fe3O4/BTSA samples showed a
o

broad exo-thermic peaks at range 200 - 450 C which is due to thermal
decomposition of two organic components IBA and BTSA. The results
confirmed the presence of inhibitors on the surface of Fe3O4 nanoparticles.
Surface potentials of Fe3O4 and modified Fe3O4by IBA and BTSA nanoparticles

Figure 3.30. Surface charge
distribution on Fe3O4 nanoparticles
modified by IBA and BTSA

Figure 3.30 shows the surface charge distribution for Fe 3O4
nanoparticles modified by IBA and BTSA. For the Fe 3O4/IBA and
Fe3O4/BTSA nanoparticles, the average surface charge was shifted to a
more negative region in comparision with Fe3O4 nanoparticles. Average
Zeta potential of Fe3O4/IBA and Fe3O4/BTSA nanoparticles were -27,29mV
and -29.61 mV, respectively. The results showed the uniform on surface
potential of Fe3O4 modified by inhibitor, especially by IBA.
OOC
HOOC

H

HO

OH

COO

OH

n
Indole-3-butyric acid (IBA)
COO
COO

N

OOC

H

N

O

O

H

H
N


To explain these results, we assume that IBA molecules carried
positive charge on N atoms and surface of Fe3O4 particles had negative
charge (The negative charge on the particles surface can be attributed to the
adsorption of -OH group from the alkaline medium during the
hydrothermal reaction). IBA molecules adsorption on Fe 3O4 particles
surface through –OH groups and created N…O which connected IBA and
Fe3O4 nanoparticles. In the outside, COO- groups carried negative charge
which shifted surface potential of particles to a more negative region.

to Cmax

60

IBA

50

BTSA

40

N độ chất hấp

phụ(mg/g)

The increasing negative charge of modified samples in comparison
with pure sample showed show that surface of Fe 3O4 particles were
changed. Along with FTIR and TGA results confirm that IBA and BTSA
molecules presence on the surface of Fe3O4.
The absorption and release of organic inhibitors on the surface of

The result showed that the time of two samples was
30

* The release of inhibitors in distilled water with three pH value ,
from the modified Fe3O4 particles.
To show the IBA effect on the corrosion protection, the release of IBA
in distilled water, from the IBA– Fe 3O4 particles was measured by UV–Vis
spectroscopy for three pH value

16


Hàm lượng chất ức chế giải thoát)(%

50
IBA

40

Figure 3.33. Release amount of IBA
and BTSA from the modified Fe3O4

BTSA

30
20

particles vs pH in distilled water

10

60

Fe3O4/IBA

modified by organic inhibitors nanoparticles

40
20
0
-20

It observed that

-40
-80

-60
-100

-15000

-10000 -50000500010000 15000

magnetic property of

Fe3O4 nanoparticles was unchanged when

H(Oe)

absorpted the organic inhibitors on the surface.

comparison with the blank solution and the current densities are
significantly lower. For both types of magnetite, accumulation of particles
on the carbon steel surface was observed after the electrochemical
measurements. This observation can explain the results observed in the
presence of the nanoparticles. However, for the solution containing the
Fe3O4/IBA, the corrosion potential is shifted toward anodic values and the
anodic current densities are lower, similar to the curve obtained in the
presence of free IBA. The electrochemical results showed the inhibitive
effect of the IBA on the corrosion of the carbon steel and confirmed that the
IBA molecules are attached on the Fe3O4 nanoparticles.

Figure 3.36. Electrodes after 24 hours immersion in 0.1M
NaCl solution
Figure 3.37. Corrosion potentials vs time
of epoxy coating and epoxy coating containing
particles

18


Figure 3.37. showed the similar trend of the corrosion potentials of
carbon steel coated by epoxy coating and epoxy coating containing
nanoparticles. During 20 days immersion in NaCl solution, corrosion
potentials of all samples increasing strongly and decreased slowly after
that. Corrosion potential values of epoxy/Fe3O4 coating and
epoxy/Fe3O4/IBA coating were higher than this value of pure epoxy coating
due to corrosion inhibition of nanoparticles at the steel/coating interface.
3.2.2.3. Electrochemical impedance of epoxy coating containing Fe 3O4
modified by corrosion inhibitors


Figure 3.41. SEM images of a
fracture surface of epoxy coating
containing 3 % wt. Fe3O4 modified by
corrosion inhibitor
Epoxy/Fe3O4/BTSA

Epoxy/Fe3O4/IBA

20