Nghiên cứu chế tạo lớp phủ polyme nanocompozit bảo vệ chống ăn mòn sử dụng nano oxit sắt từ fe3o4 tt tiếng anh

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

st

1 Reviewer: ...................................................................................
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nd

2 Reviewer: ..................................................................................
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rd

3 Reviewer: ..................................................................................
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The dissertation will be defended at Graduate University of Science
And Technology, Vietnam Academy of Science and Technology, 18 Hoang
Quoc Viet, Cau Giay District, Hanoi City.
At… hour… date… month… 2019
The dissertation can be found in National Library of Vietnam and
library of Graduate University of Science And Technology, Vietnam
Academy of Science and Technology

ii


INTRODUCTION
1. Background
Metal and metal alloys are base materials that people have used for a
long time and play an important role in our new world without replacing.

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

- Synthesis and characterization of Fe3O4 nanoparticles, -Fe2O3
nanoparticles and γ-Fe2O3 nanoparticles by hydrothermal method. Compare
the corrosion protection ability of epoxy film containing synthetic iron
oxide particles.
- Fabrication and evaluation of steel corrosion protection effect of
epoxy membrane containing magnetic iron oxide nanoparticles and nano
iron oxide from organic denaturation with some silane compounds and with
corrosion inhibiting compound.
- Research on using microstructure analysis methods to clarify the
role of nanoparticles in improving the anti-corrosion protection of products.
DISSERTATION CONTENTS
CHAPTER 1. LITERATURE REVIEW
The literature review provided an overview:
 Introduction about iron oxides and their applications containing: FeO, α-Fe 2O3, γFe2O3, Fe3O4. This chapter focus on characteristic of structure, properties and
thermal synthesis method of Fe3O4.
 Introduction about surface modification of Fe 3O4 nanoparticles: surface properties,
modification method of particles, stabilization of particle surface
 Introduction about corrosion protection of coating prepared by polymer
nanocomposite.

CHAPTER 2.
EXPERIMENTS 2.1. Material and equipments
 FeSO4.7H2O , FeCl3.6H2O, KOH, C2H5OH, Xylene, HCl, HNO3,

N-(2-Aminoethyl)-3-aminopropyltrimethoxysilane
(APTS),
Diethoxy(methyl)phenylsilane (DMPS), Tetraethoxysilane ( TEOS),
Indol 3-Butyric axit (IBA), Irgacor 252, 2-(1,3-Benzothiazol-2-ylthio)
succinic axit (BTSA), epoxy resin (Diglycidyl ete of Bisphenol A,
Epotec YD 011-X75) and hardener polyamide 307D-60.

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

added to the solution then stirring and using ultrasonic vibration. The
o

reaction mixture was kept at 60 C for 60 minutes with mechanical
o
stirring. Afterwards, particles were washed and dried in oven at 50 C
for 10 hours.
 Modification Fe3O4 nanoparticles with corrosion inhibitors: IBA (or
BTSA) was dissolved in a water/ethanol mixture (1/19 ratio). Then,
the Fe3O4 nanoparticles were dispersed by disperser and then
mechanically stirred and ultrasonic vibrated for 15 minutes and 30
minutes, respectively. The mixture was left in 3 hours. Afterwards, the
precipitate was filtered and washed with ethanol several times to
remove the excess IBA. The modified Fe3O4 nanoparticles were
o
finally dried in a vacuum oven at 60 C for 10 hours.
2.4. Preparation of epoxy coating containing iron oxides and modified
iron oxides
Carbon steel plates (150 mm x 100 mm x 2 mm) were used as
substrates which were cleaned and dried before coating. The pre-polymer
mixtures (with or without particles) were applied by spin-coating at a speed
of 600 rpm for 1 min. After polymerization and drying at room temperature
for 24 hours, the coatings were about 30 µm.
3


2.5. Analytical characterizations for nanoparticles
FT-IR analysis, X-rays diffraction, UV-Vis, TGA analysis, SEM, Zeta
potential, saturation magnetization.
2.6. Method for evaluation properties of coatings:

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

FTIR spectrum of Fe3O4 nanoparticles is shown in Figure 3.3. Figure
3.3. FT-IR spectrum of
Fe3O4 nanoparticles
The result showed that absorptions in
–1

–1

3431 cm and 1629 cm are responsible to
O-H that adsorbed on the surface of the
–1
nanoparticles and absorption at 586 cm and
–1
Số sóng (cm )
447 cm are related to Fe-O bonds in
nanoparticles.
3.1.2. Characterization of α-Fe2O3 nanoparticles
-1

Figure 3.4. The XRD pattern of
pure magnetite obtained by
hydrothermal method

Figure 3.4. showed the diffraction pattern that allowed for
unequivocal identification of hematite; using the ICSD (Inorganic Crystal
Structure Database) reference code 01-079-0007 for hematite the
diffraction peaks were identified.

Figure 3.5. SEM micrographs of α-Fe2O3 particles obtained
by hydrothermal method

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

α-Fe2O3
nanoparticles is shown in Figure 3.6. The

–1

–1

and 1625 cm are responsible to O-H that
absorbed on the surface of the nanoparticles.

4000

3000

2000

1000

-1

Số sóng (cm )

Figure 3.6. FT-IR spectrum of
α-Fe2O3 nanoparticles
3.1.3. Characterization of γ-Fe2O3 nanoparticles
Figure 3.7. The XRD pattern of a)
Fe3O4 và b) γ-Fe2O3
In comparison with XRD pattern of Fe3O4,
the peaks were shifted slightly that allowed for
unequivocal identification of maghemite; using

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)

-40
-80

γ-Fe2O3(b)

-100

05000

10000

15000

These results showed clearly that the Fe3O4 and

-15000 -10000 -5000

H (Oe)

γ- Fe2O3 nanoparticles exhibited superparamagnetic
behavior which obtained the highest magnetization saturation value (Ms) of
81 emu/g and 60 emu/g, respectively.

Figure 3.9. SEM micrographs of γ-Fe2O3 nanoparticles
The results SEM confirm that γ-Fe2O3 nanoparticles are similar in
size with Fe3O4 nanoparticles.
6

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(%)

1122

2938

100

–1

in 3420 cm
and 1625 cm
are
responsible to O-H that adsorbed on the
surface of the nanoparticles and
–1

–1

absorption at 565 cm and 476 cm are
related to Fe-O bonds in nanoparticles.

3.1.4. Effect of nanoparticles on corrosion protection of epoxy coating
Corrosion protection of epoxy coating containing 3% wt. particles
was demonstrated by electrochemical impedance spectroscopy (EIS).
After 1 hour immersion in 3 % NaCl solution, electrolyte had not
penetrated in the coating yet. After 14 days immersion, the EIS diagram of
pure epoxy coating presented two circles well defined. In the other hand,
EIS diagram of epoxy/ γ-Fe2O3 showed that a third time constant appeared
in the medium frequency range because of the reaction between particles
and epoxy coating. The particles filled the holes in the surface of coating
and prevented the electrochemical process taking place.

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

9

10

Figure 3.15. Variation of Z1Hz
values with immersion time in NaCl
3% solution of pure epoxy coating,
epoxy coating containing 3% wt.
iron oxides: epoxy/Fe3O4, epoxy/
α-Fe2O3 và epoxy/γ-Fe2O3

Epoxy
Epoxy/Fe3O4
Epoxy/γ-Fe2O3
Epoxy/α-Fe2O3

10

8

10

7

|Z|1Hz

10 6

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)

Pure epoxy
Epoxy/Fe3O4
Epoxy/α-Fe2O3
Epoxy/γ-Fe2O3

3,5
6,0
7,0
6,2

180
>200

Diện tích bong rộp %

120
MT

NF AF G-AF

Figure 3.16. Delaminated area
showing the adhesive loss vs
immersion
time in water: pure epoxy coating (a),

80

(a)

40

(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

oxides can be explained by the cooperative bonds between the iron oxides
(Fe3O4, α- Fe2O3 or γ-Fe2O3) and the oxide layer at the steel/coating
interface which prevent water penetrated through the coating.
3.1.6. Morphology of epoxy coating containing 3% wt. Fe3O4
nanoparticles

Figure 3.17. SEM images of a fracture surface of epoxy coating
containing 3 % wt. Fe3O4
SEM imagines show the agglomeration of Fe 3O4 particles in epoxy
coating. Therefore modifying surface of particles by organic compounds was
necessary which improved the dispersion of Fe 3O4 particles in epoxy matrix. The
particular properties of particles will not be changed in modifying process.
9


3.2. CHARACTERIZATION OF CORROSION PROTECTION OF
EPOXY CONTAINING Fe3O4 AND MODIFIED Fe3O4
3.2.1. Characterization of corrosion protection of epoxy coating
containing silane modified Fe3O4 nanoparticles
3.2.1.1. Characterization of Fe3O4 nanoparticles modified by silanes
FT-IR analysis
Figure 3.18. FT-IR spectrum of Fe3O4
and Fe3O4 modified by silanes: ATPS,
DMPS, and TEOS
The spectrum of silane modified Fe3O4 nanoparticles presents the
-1

-1

bands at 1120 cm and 1050 cm characteristic of Si-O-Fe and Si-O-Si

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)

100
80

Fe3O4/APTS

60

Fe3O4/DMPS
Fe3O4/TEOS

40
20
0
-20
-40
-60
-80
-100
-15000

75

The hysteresis loops of the modified

70

65

2500

-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

frequencies were not determined. When immersion time reach to 42 days, the
EIS diagram of all coatings presented two circles well defined. This indicates
that electrolyte penetrated in the coating and the corrosion process occurred at
metal surface. However, the impedance values of epoxy coating
11


containing silane modified Fe3O4 nanoparticles were high after along
immersion time. This result showed that surface modification by silanes
enhanced protection efficiency of Fe3O4 on epoxy coating.
Figure 3.22. Nyquist
plots for the epoxy coating
containing 3 % wt.
Fe3O4/DMPS

Figure 3.23. Nyquist
plots for the epoxy
coating
containing 3 % wt.
Fe3O4/TEOS

Fe3O4/DMPS

Fe3O4/TEOS

The variation of Z1Hz values with immersion time in NaCl 3%
solution are presented in Figure 3.24.
The Z1Hz value of epoxy/Fe3O4/DMPS were equivalent with the one
of epoxy/Fe3O4 while epoxy/Fe3O4/APTS and epoxy/Fe3O4/TEOS have
highest impedance modulus. The best values and best protection were

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

100

Thời gian (ngày)

The SEM micrographs (figure 3.25 to 3.27) showed that surface
modification Fe3O4 by silanes decreased the cluster in the epoxy matrix
significantly. The images indicated that Fe3O4/APTS had highest dispersion
in the polymer matrix.
12


Epoxy/Fe3O4/APTS

Figure 3.25. SEM images of a fracture surface of epoxy coating
containing 3% wt. Fe3O4/APTS

Epoxy/Fe3O4/DMPS

Figure 3.26. SEM images of a fracture surface of epoxy coating
containing 3% wt. Fe3O4/DMPS

Epoxy/Fe3O4/TEOS

Figure 3.27. SEM images of a fracture surface of epoxy
coating containing 3% wt. Fe3O4/TEOS
Physical mechanical properties of epoxy coating containing silane
modified Fe3O4
The increasing of wet adherence of epoxy coating containing iron oxide
have the reason that the interaction between iron oxides (Fe 3O4, α- Fe2O3 or

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

Figure 3.28. Delaminated area showing

8
0

the adhesive loss vs immersion time in

Diện
tích
bong
rộp %

water: epoxy coating with Fe3O4 (a),

6
0

(a)

Fe3O4/APTS(b), Fe3O4/DMPS (c), and
(b)(c) (d)

4
0

Fe3O4/TEOS (d)

3

20

6

1

10

2
NF-ATS

NF

24

3
NF-DMPS

4

NF-TEOS

Thời gian (giờ)

0

1694

3000
2000

-1
-1
SốBướcsóng sóng(cm (cm) )

Độ truyềnTqua(%)(%)

435 593
740

503

2602

2947

3393

3036

qu
a

Độ truyền
4000

Fe3O4

447

585

1099
1057

1386
1455
1427

1630
1629

IBA

1621

2921

3435

Fe3O4/IBA

(%
)

T (%)

Fe3O4

3433

3.2.2. Corrosion protection performance of epoxy coating with Fe3O4
nanoparticles modified by organic inhibitors
3.2.2.1. Characterization of Fe3O4 nanoparticles modified by organic
inhibitors
FT-IR and DTA/TG analysis

1000

4000


1 -1

(cm ) )

(a) : Fe3O4 modified by IBA and pure IBA (b): Fe3O4 modified by BTSA and pure
BTSA Figure 3.29. FT-IR spectrum of Fe3O4 and Fe3O4 modified by IBA and

pure IBA (a), Fe3O4 modified by BTSA and pure BTSA (b)
The spectrums of all samples presents the bands characteristic for –OH
group and Fe-O groups. The –CH2 characteristic peaks were observed at 2921
-1

-1

cm (Fe3O4/IBA) and 2920 cm (Fe3O4/BTSA) while C=C of –C6H5
14


-1

-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

Fe3O4

N H

HO

H

H
HO

HO

H
O N

Fe3O4

N O
OH

Fe3O4

OH

HO

OH

HO

OH

COO

OH

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

N

OOC

H

N

O

O

H

H
N

Fe3O4

O

O

N
H

H

O

O

N

COO

H N

OOC

OOC

Figure 3.31. Absorption model of IBA molecules on the surface of
Fe3O4 nanoparticles
15

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

Fe3O4 nanoparticles
* The adsorption of organic inhibitors on the surface of Fe3O4
nanoparticles
30
20
10


ồng

0
0

50

100

150

200

Thời gian (phút)

minutes and Cmax was over 50 mg/g.

Figure 3.32. The absorption
diagram of organic inhibitors on
the
surface of Fe3O4 nanoparticles

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

0

It is observed that the corrosion
2

4

6

8

1012

pH

M (emu/g)

inhibitor release increases for the high pH
value. It can be recalled that the corrosion process induces an increase of
the local pH due to the cathodic reaction of oxygen reduction. Thus, the
release of IBA and BTSA, favored in alkaline conditions, will lead to the
corrosion inhibition of the carbon steel.
Magnetic property of Fe3O4 modified by organic inhibitors
nanoparticles
Figure 3.34. Hysteresis loops of Fe3O4
100

Fe3O4/BTSA

80

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.

3.2.2.2. Polarization curves
Figure 3.35. Polarization curves
obtained for the carbon steel
electrode
after 24 h of immersion in the
0.1 M NaCl solution: (○) 3%
wt. Fe3O4,
(●)3% wt. Fe3O4/IBA, (▼)10
3
M IBA, (—)blank solution

-


17


The polarization curves obtained for the carbon steel in the 0.1 M
NaCl solutions containing Fe3O4 or IBA–Fe3O4 nanoparticles are presented
in Figure 3.35.
-3

In solution with 10 M IBA, it can be seen that the corrosion potential
is shifted in the anodic direction (about 100 mV) and the anodic current
densities are significantly lower by comparison with the blank solution,
particularly near the corrosion potential. This result confirmed the
inhibitive properties of IBA and showed that the compound is an anodic
inhibitor. The polarization curves obtained in the presence of Fe 3O4 or
IBA–Fe3O4 presented similar shape.
The corrosion potential is shifted toward cathodic potentials by

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 3.38.Nyquist plots for the epoxy coating containing 3%
wt. Fe3O4 nanoparticles modified by IBA
After 14 days of immersion, the diagrams of epoxy/Fe 3O4/BTSA
coating was characterized by one capacitive loop and epoxy/Fe 3O4/IBA
coating was characterized by two well defined capacitive loops following:
one in the the high-frequency part and one in the low- frequency part. This
results indicates the inhibitive action and barrier property of Fe 3O4/BTSA
was higher than this of Fe3O4/IBA.
After 84 days of immersion, the second loop appeared in the diagrams
of all samples. Impedance value of epoxy/Fe 3O4/IBA coating decreased
strongly but this value of epoxy/Fe3O4/BTSA coating was still better.

19


Figure 3.39. Nyquist plots for the epoxy coating containing 3%
wt. Fe3O4 nanoparticles modified by BTSA
Figure 3.40. Variation of Z1Hz
values with immersion time in NaCl 3%
solution of epoxy coating containing 3%
wt. Fe3O4 and modified Fe3O4
nanoparticles

After 14 days of immersion, the impedance modulus of epoxy coating
containing Fe3O4/BTSA decreased slightly and reached to stability state in
the next period of time. The impedance modulus of epoxy coating
containing Fe3O4/IBA decreased rapidly and was similar with this value of
epoxy coating containing Fe3O4 after 84 days of immersion.
3.2.2.4. Morphology of epoxy coating containing Fe3O4 modified by
corrosion organic inhibitor

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