Dissertation summary: Study on effect of Fe3O4 nanoparticles on polymer nanocomposite coating for corrosion protection

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.

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: Assoc Prof Dr Trinh Anh Truc Institute for Tropical Technology - Vietnam Academy of Science and Technology Assoc Prof Dr Nguyen Xuan Hoan Dept Physical Chemistry, Faculty of Chemistry, Hanoi University of Science - Vietnam National University 1st Reviewer: 2nd Reviewer: 3rd Reviewer: 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 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 - 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” 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 LITERATURE REVIEW The literature review provided an overview:  Introduction about iron oxides and their applications containing: FeO, αFe2O3, γ-Fe2O3, Fe3O4 This chapter focus on characteristic of structure, properties and thermal synthesis method of Fe3O4  Introduction about surface modification of Fe3O4 nanoparticles: surface properties, modification method of particles, stabilization of particle surface  Introduction about corrosion protection of coating prepared by polymer nanocomposite CHAPTER EXPERIMENTS 2.1 Material and equipments  FeSO 7H O , FeCl 6H O, KOH, C H OH, Xylene, HCl, HNO , 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 reaction was conducted at 180oC for 15 h After reaction, the precipitate was washed with distilled water and dried in a vacuum oven  Synthesis Fe3O4 nanoparticles: a mixture of FeCl3.6H2O/FeSO4.7H2O (molar ratio Fe2+/Fe3+ = 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 150oC for h After reaction, the precipitate was washed with distilled water to remove impurity ions (Cl- , SO42- , K+ ) and dried in a vacuum oven  Synthesis γ-Fe2O3 nanoparticles: Thermal treatment process for synthesized Fe3O4 nanoparticles at190oC for 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) Fe3O4 was added to the solution then stirring and using ultrasonic vibration The reaction mixture was kept at 60oC for 60 minutes with mechanical stirring Afterwards, particles were washed and dried in oven at 50 oC 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 hours Afterwards, the precipitate was filtered and washed with ethanol several times to remove the excess IBA The modified Fe3O4 nanoparticles were finally dried in a vacuum oven at 60oC 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 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 After polymerization and drying at room temperature for 24 hours, the coatings were about 30 µm 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 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 %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 3431 cm–1 and 1629 cm–1 are responsible to O-H that adsorbed on the surface of the nanoparticles and absorption at 586 cm–1 and 447 cm–1 are related to Fe-O bonds in Số sóng (cm ) 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 1625 3420 565 476 %T FTIR spectrum of α-Fe2O3 nanoparticles is shown in Figure 3.6 The result showed that absorption at 565 cm–1 and 476 cm–1 are related to Fe-O bonds in nanoparticles and absorptions in 3420 cm–1 and 1625 cm–1 are responsible to O-H that absorbed on the surface of the nanoparticles 4000 3000 2000 1000 Số sóng (cm-1) 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 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 Figure 3.8 Hysteresis loop of Fe3O4 and (a) γ- Fe2O3 particles Image of magnetite and (b) maghemite nanoparticles were manipulated by magnet (small image) These results showed clearly that the Fe3O4 and 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 100 80 M (emu/g) 60 40 20 -20 -40 Fe3O4 (a) γ-Fe2O3(b) -60 -80 -100 -15000 -10000 -5000 5000 10000 15000 Figure 3.9 SEM micrographs of γ-Fe2O3 nanoparticles The results SEM confirm that γ-Fe2O3 nanoparticles are similar in size with Fe3O4 nanoparticles 623 3436 3000 3000 2000 2000 -1)-1) SốSốsóng (cm sóng (cm 1000 1000 577 %T T (%) 1632 1122 2938 100 Figure 3.10 FT-IR spectrum of γ -Fe2O3 nanoparticles The result showed that absorptions in 3420 cm–1 and 1625 cm–1 are responsible to O-H that adsorbed on the surface of the nanoparticles and absorption at 565 cm–1 and 476 cm–1 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 hour immersion in % 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 % wt α-Fe2O3 nanoparticles Epoxy/α-Fe2O3 After 42 days of immersion, for the epoxy coating containing α-Fe2O3, 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-Fe2O3 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 % wt γ-Fe2O3 Figure 3.14 Nyquist plots for the epoxy coating containing % wt Fe3O4 |Z|1Hz 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/ αFe2O3 epoxy/γ-Fe2O3 10 10 10 10 10 10 Epoxy Epoxy/Fe3O4 Epoxy/γ-Fe2O3 Epoxy/α-Fe2O3 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 Fe3O4 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 bands at 1120 cm-1 and 1050 cm-1 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 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 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 Fe3O4 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 100 80 M (emu/g) 60 Fe3O4/APTS Fe3O4/DMPS Fe3O4/TEOS 40 20 -20 75 The hysteresis loops of the modified 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 -40 70 -60 -80 -100 -15000 -10000 65 -5000 2500 5000 3500 10000 4500 15000 Figure 3.21 Nyquist plots for the epoxy coating containing % wt Fe3O4/APTS Fe3O4/APTS After hour immersion in % 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 Fe3O4/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 % wt Fe3O4/DMPS Figure 3.23 Nyquist plots for the epoxy coating containing % 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 10 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 10 10 Fe3O4 Fe3O4/APTS Fe3O4/DMPS Fe3O4/TEOS 10 10 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 (Fe3O4, α- Fe2O3 or γFe2O3) and iron oxides occur at the surface of carbon steel prevent water penetrated through the coating The pull-off strength of epoxy coating containing Fe3O4/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 Pull-off strengths impact strengths Samples (MPa) (kg/cm) Epoxy - Fe3O4 5,9 >200 Epoxy - Fe3O4/ATS 7,1 Epoxy - Fe3O4/DMPS 6,0 Epoxy - Fe3O4/TEOS 7,8 Figure 3.28 Delaminated area showing the adhesive loss vs immersion time in water: epoxy coating with Fe3O4 (a), Fe3O4/APTS(b), Fe3O4/DMPS (c), and Fe3O4/TEOS (d) Diện tích bong rộp % 100 80 60 (a) 40 (b)(c) (d) 20 31 24 10 Thời gian (giờ) NF NF-ATS NF-DMPS NF-TEOS 3000 2000 SốBước sóng sóng (cm-1(cm ) -1) 2000 447 585 755 1197 1160 588 1110 450 1099 1630 3000 1422 1455 2852 2924 1710 1000 1385 1630 2920 2849 3433 503 3440 (%)(%) Độ truyềnTqua 593 435 BTSA 740 1694 4000 4000 Fe3O4/BTSA 3435 Fe3O4 447 585 1099 1057 1630 2947 1621 1455 1427 2602 3036 IBA 1386 1629 3435 2921 Fe3O4/IBA 3393 (%)(%) T qua Độ truyền 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 SốBước sóng sóng (cm-1(cm ) -1) (a) : Fe3O4 modified by IBA and pure IBA (b): Fe3O4modified 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 cm-1 (Fe3O4/IBA) and 2920 cm-1 (Fe3O4/BTSA) while C=C of –C6H5 14 groups were observed at band 1385 cm-1-1630 cm-1 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 Fe3O4/BTSA samples showed a broad exo-thermic peaks at range 200 - 450oC 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 Fe3O4 nanoparticles modified by IBA and BTSA For the Fe3O4/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 OH HO OH HO N H N Fe33O O44 Fe HO H OH H Fe3O4 O H N H HO HO O OH COO OH n Indole-3-butyric acid (IBA) CO O CO O N N H O O O OC H H N Fe3O4 O O N H O H O N CO O H N O OC O OC Figure 3.31 Absorption model of IBA molecules on the surface of Fe3O4 nanoparticles 15 Nồng độ chất hấp phụ (mg/g) 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 Fe3O4 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 The increasing negative charge of modified samples in comparison with pure sample showed show that surface of Fe3O4 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 60 BTSA 50 40 Figure 3.32 The absorption diagram of organic inhibitors on the surface of Fe3O4 nanoparticles IBA 30 20 10 0 50 100 150 200 Thời gian (phút) The result showed that the time to Cmax of two samples was 30 minutes and Cmax was over 50 mg/g * 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– Fe3O4 particles was measured by UV–Vis spectroscopy for three pH value 16 Hàm lượng chất ức chế giải thoát (%) 50 IBA BTSA Figure 3.33 Release amount of IBA and BTSA from the modified Fe3O4 particles vs pH in distilled water 40 30 20 10 It is observed that the corrosion pH 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 10 12 100 80 M (emu/g) 60 Figure 3.34 Hysteresis loops of Fe3O4 modified by organic inhibitors nanoparticles Fe3O4/IBA Fe3O4/BTSA 40 20 -20 -40 -60 -80 -100 -15000 -10000 -5000 5000 10000 15000 H(Oe) It observed that magnetic property of Fe3O4 nanoparticles was unchanged when 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, (▼)10-3M 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 In solution with 10-3M 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 Fe3O4 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 Fe3O4 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/Fe3O4/BTSA coating was characterized by one capacitive loop and epoxy/Fe3O4/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 Fe3O4/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/Fe3O4/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 % wt Fe3O4 modified by corrosion inhibitor Epoxy/Fe3O4/BTSA Epoxy/Fe3O4/IBA 20 In comparison with SEM image of epoxy/Fe3O4 coating, the clusters in the epoxy matrix of epoxy coating containing % wt Fe3O4 modified by corrosion inhibitor was reduced significantly and nanoparticles had a good dispersion in matrix 3.2.2.5 Characterization physical mechanical properties of epoxy coating containing Fe3O4 modified by corrosion inhibitor Table 3.3 Pull-off strength and impact strength of epoxy coating containing Fe3O4 and Fe3O4 modified by corrosion inhibitor Samples Pull-off strength Impact strength (MPa) (kg/cm) Epoxy /Fe3O4 5,9 >200 Epoxy /Fe3O4/BTSA 6,6 Epoxy/Fe3O4/IBA 7,4 The dry adherence detemined by pull-off strength of modified samples were higher than this value of unmodified sample Among samples, pull-off strength of coating containing IBA was highest value at 7.4 MPa After 24 hours immersion in water, modified Fe3O4 nanoparticles improved the wet adherence of epoxy coating in comparison with coating containing pure Fe3O4 It can be explained by the releasing IBA and BTSA molecules in water and their reaction with iron oxides on the surface of steel Diện tích bong rộp (%) 100 80 NF NF-BTSA Figure 3.42 Delaminated area showing the adhesive loss vs immersion time in water: epoxy/Fe3O4 coating (a), epoxy/Fe3O4/BTSA coating (b), Fe3O4/IBA coating (c) NFIBA 60 (a) 40 (c) 20 (b) 3 24 10 Thời gian ngâm (giờ) 3.2.2.6 Salt spray testing Pictures of the samples after 240 h exposure to the salt spray are shown in Figure 3.47 and the evaluation of the corrosion behavior, according to ASTM D1654, is presented in Table 3.4 Rating number for pure epoxy coating was and for epoxy coating containing particles was or 21 The salt spray results indicated that the presence of Fe3O4 or Fe3O4 modified by IBA and BTSA improved the corrosion protection of the carbon steel When the amount of nanoparticles in epoxy matrix increased, epoxy/Fe3O4 coating changed insignificantly Due to good dispersion of Fe3O4 modified by corrosion inhibitor in epoxy matrix, amount of modified particles increased lead to increase barrier property and corrosion inhibition of coating Table 3.4 Salt spray test results after 240 h exposure according to ASTM D1654 standard Samples Creepage from scribe Rust creepage Rating number (mm) Epoxy 1,8 Epoxy- 3% wt.Fe3O4 0,8 Epoxy- 5% wt.Fe3O4 0,9 Epoxy- 7% wt.Fe3O4 0,9 Epoxy- 3% wt.Fe3O4/IBA 0,8 Epoxy- 5% wt.Fe3O4/IBA 0,6 Epoxy- 7% wt.Fe3O4/IBA 0,1 Epoxy- 3% wt.Fe3O4/BTSA 0,7 Epoxy- 5% wt.Fe3O4/BTSA 0,5 Epoxy- 7% wt.Fe3O4/BTSA 0,1 Figure 3.47 Salt spray test results obtained after 240 h for the carbon steel coated with the epoxy, epoxy/Fe3O4 and epoxy/Fe3O4 modified by IBA and BTSA in different amount: 3% wt., 5% wt.and 7% wt 22 CONCLUSIONS After a period of study, the thesis has obtained the following results: Fe3O4, α-Fe2O3 and γ- Fe2O3 nanostructures were synthesized via hydrothermal method The X-ray diffraction (XRD) and FT–IR analysis confirmed that as-prepared nanoparticles were pure spinel Fe3O4, α-Fe2O3 and γ- Fe2O3 without any impurity The hysteresis loops decated that Fe3O4 and γ- Fe2O3 nanoparticles were superparamagnetic Characterization of corrosion protection of epoxy coating containing nanoparticles showed that the presence of iron oxides in epoxy matrix significantly improved the barrier properties of the coating, especially Fe3O4 Fe3O4 was modified by three kinds of silane: APTS, DMPS and TEOS It was proved that the surface modification happened The negative charge on the surface of particles decreased but properties of particles was unchanged Silane modified Fe3O4 improved the corrosion protection of epoxy coating, especially with Fe3O4/APTS Surface of Fe3O4 nanoparticles was modified by two corrosion inhibitors: IBA and BTSA Corrosion inhibitor released for high pH value which showed the corrosion protection of modified nanoparticles in epoxy matrix Epoxy coating containing Fe3O4 modified BTSA inhibitor showed its corrosion protection carbon steel and the good dispersion nanoparticles in matrix NEW CONTRIBUTIONS OF THE DISSERTATION Fe3O4 nanoparticles was synthesized by hydrothermal method which was modified by three kinds of silane (N-(2-aminoethyl)-3-aminopropyltrimethoxysilan, diethoxy(methyl)phenylsilan, tetraethoxysilan) and corrosion inhibitors (Indol 3Butyric axit 2-(1,3-Benzothiazol-2-ylthio) succinic axit) Modifying Fe3O4 nanoparticles increased the dispersion in polyme matrix Preparation and characterization of epoxy coating containing Fe3O4 and modified Fe3O4 which coated on CT3 carbon steel The results demonstrated that epoxy coating containing magnetite and modified magnetite are available for replacing traditional pigment in corrosion protection coating 23 PUBLICATIONS Nguyen Thu Trang, Trinh Anh Truc, To Thi Xuan Hang, Le Thi Lien, Nguyen Xuan Hoan, Preparation of iron oxide nanoparticles using an epoxy coating for corrosion protection of carbon steel, Vietnam Journal of Chemistry 50 (6B) (2012), 71-76 Tran Xuan Hoi, Nguyen Phi Hung, Nguyen Thu Trang, Nguyen Thi Cam Ha, Nguyen Xuan Hoan, To Thi Xuan Hang, Trinh Anh Truc, Preparation and investigate of corrosion protection capacity of epoxy/hematit nanocomposite coating for carbon steels, Vietnam Journal of Science and Technology 51 (3A) (2013) 250-256 Đặng Thế Bách, Trần Xuân Hợi, Nguyễn Thu Trang, Trịnh Anh Trúc, Phạm Đức Thắng, Nguyễn Xuân Hoàn, Hydrothermal synthesis and property of nano Fe3O4 doping by Cobalt or Zinc, Vietnam Journal of Chemistry 51(2C) (2013) 723-728 Nguyen Thu Trang, Trinh Anh Truc, Nguyen Xuan Hoan, Phan Thi Trang, Thai Thu Thuy, To Thi Xuan Hang, Synthesis and modification of Fe3O4 nanoparticles by alkyl ammonium of 2-benzothiazolythio succinic acid for enhancement of the corrosion resistance of epoxy coating on the carbon steel surface, Journal of Science and Technology 53 (4A) (2015) 145-152 Nguyễn Thu Trang, Trịnh Anh Trúc, Nguyễn Xuân Hoàn, Nghiên cứu ảnh hưởng silan hữu biến tính đến tính chất màng sơn epoxy cứa nano sắt từ, Tạp chí Hóa học, 6e1/54, (2016), 17-22 Anh Truc Trinh, Thu Trang Nguyen, Thu Thuy Thai, Thi Xuan Hang To, Xuan Hoan Nguyen, Anh Son Nguyen, Maëlenn Aufray & Nadine Pébère, Improvement of adherence and anticorrosion properties of an epoxy polyamide coating on steel by incorporation of an indole-3 butyric acidmodified nanomagnetite, Journal of Coatings Technology and Research, 13 (3) (2016), 489-499 24 ... 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. .. 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... 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