Study on effect of Fe3O4 nanoparticles in polymer nanocomposite coating for corrosion protection

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 ii 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 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 1 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” 2 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- Fe2O3, 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 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 3 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 7 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 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). 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 50oC 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 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 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. 4 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. 5 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 nanoparticles. 3.1.2. Characterization of α-Fe2O3 nanoparticles 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 Số sóng (cm-1) % T 6 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. 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. Figure 3.8. Hysteresis loop of Fe3O4 and γ- Fe2O3 particles. Image of magnetite and maghemite nanoparticles were manipulated by magnet (small image) These results showed clearly that the Fe3O4 and 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. M ( em u /g ) H (Oe) -100 -80 -60 -40 -20 0 20 40 60 80 100 -15000 -10000 -5000 0 5000 10000 15000 (a) (b) γ-Fe2O3(b) Fe3O4 (a) 4 7 6 5 6 5 1 6 2 5 3 4 2 0 1000 2000 3000 4000 Số sóng (cm-1) % T 7 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 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 Số sóng (cm-1) % T 3000 2000 1000 100 3 4 3 6 2 9 3 8 1 6 3 2 6 2 3 5 7 7 1 1 2 2 Số sóng cm-1) T ( % ) 3000 2000 1000 Epoxy/α-Fe2O3 8 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 3 % wt. γ-Fe2O3 Figure 3.14. Nyquist plots for the epoxy coating containing 3 % wt. Fe3O4 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 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. 10 5 10 6 10 7 10 8 10 9 10 10 0 20 40 60 80 100 Epoxy Epoxy/γ-Fe2O3 Epoxy/Fe3O4 Epoxy/α-Fe2O3 Thời gian (ngày) |Z | 1 H z 9 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 3,5 180 Epoxy/Fe3O4 6,0 >200 Epoxy/α-Fe2O3 7,0 Epoxy/γ-Fe2O3 6,2 Figure 3.16. Delaminated area showing the adhesive loss vs immersion time in water: pure epoxy coating (a), epoxy coating containing 3% wt. Fe3O4 (b), 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 Fe3O4 particles in epoxy coating. Therefore modifying surface of particles by organic compounds was necessary which improved the dispersion of Fe3O4 particles in epoxy matrix. The particular properties of particles will not be changed in modifying process. 0 40 80 120 1 2 3 4 MT NF AF G-AF 3 6 10 24 (a) (b) (c) (d) Thời gian (giờ) D iệ n tí ch b o n g r ộ p % 10 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 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 Fe3O4 with APTS, DMPS and TEOS are -19.31 mV; -19.05 mV and -18.15 mV, respectively. 11 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 The hysteresis loops of the modified magnetic particles obtained using a magnetometer are show in Figure 3.20. The 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 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 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 -100 -80 -60 -40 -20 0 20 40 60 80 100 M ( em u /g ) H(Oe) -15000 -10000 -5000 0 5000 10000 15000 Fe3O4/APTS Fe3O4/DMPS Fe3O4/TEOS 2500 3500 4500 65 70 75 Fe3O4/APTS 12 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 The variation of Z1Hz values with immersion time in NaCl 3% solution are presented in Figure 3.24. The Z1Hz value of epoxy/Fe