THE UNIVERSITY OF DANANG UNIVERSITY OF SCIENCE AND EDUCATION  DUONG THI HONG PHAN IMPROVING CORROSION PROTECTION OF EPOXY RESIN BY THE MODIFIED EPOXY AND CONVERSION COATING ON METAL SUBSTRATE Major: Organic Chemistry Code: 94440114 SUMMARY OF DISSERTATION ON DOCTOR OF PHILOSOPHY IN CHEMISTRY DaNang, 2019 The dissertation was completed at THE UNIVERSITY OF SCIENCE AND EDUCATIONTHE UNIVERSITY OF DANANG Scientific Supervisors: Prof.Dr.Dao Hung Cuong Asc.Prof.Dr Le Minh Duc 1st Reviewer: 2nd Reviewer: 3rd Reviewer: The dissertation will be defended at The University of Danang-The University of Science and Education at………… The : National library of Viet Nam; The library of The University of Science and Education-The University of DaNang PREFACE Reasons for choosing the dissertation: In the paint industry, titanium dioxide (TiO2) is a white, solid, non-toxic, inexpensive and fast colour In anti-corrosion properties terms, TiO2 nanotubes are capable of extending the erosion time through the coating of corrosion agents than TiO2 nanoparticles However, TiO2 nanoparticles were dispersed in resin difficult to achieve homogeneity because of their high surface energy leading to easy aggregation and clotting, especially in high viscosity epoxy resins Once well dispersed, mechanical, durability, heat resistance and anticorrosion properties were improved Physical distribution is not enough but also a combination of physical and chemical methods Therefore, we conducted a study on synthesis of TiO2 nanotubes and the grafting surface of TNTs with silane coupling agent called 3aminopropyl triethoxylsilane (APTS) to increase homogeneity by entropy mechanism Besides, the molybdate conversion coating was highly appreciated to replace chromate (VI) ions in the field of metal protection by not only similar good corrosion resistance but also harmless inhibitor However, molybdate conversion coating was more effective in the presence of oxidizing compounds In addition, the Ti/Zr oxidizing compounds have also been rated for its ability to safe on steel surfaces in recent decades Therefore, the Zr/Ti/Mo conversion coating on the steel subtrates by chemical methods to improve the substrate protection was part of the dissertation For those reasons, we propose the dissertation : “ Improving corrosion protection of epoxy resin by the modified epoxy and conversion coating on metal substrate” The objects of the dissertation: Epoxy paint coating for metal protection by the grafted APTS on TiO2 nanotubes Simultaneously, steel subtrates were coated with the Zr/Ti/Mo conversion coating to improve the steel protection Contents of the dissertation: processing and coating of Zr/Ti/Mo layer; studying surface and composition of Zr/Ti/Mo coating on the steel surface by SEM/EDX methods; studying the mechanical properties of the coating; evaluating the corrosion resistance of Zr/Ti/Mo conversion coating by EIS and salt spray method; physical and thermal properties of epoxy resins using APTS-TNTs pigment; evaluating the corrosion resistance of that epoxy resins by EIS and salt spray methods Methods: material analysis methods: X-ray diffraction, scanning electron microscopy, BET, TEM, FTIR, TGA and DSC; evaluating methods for the mechanical properties of paint film: tape adhesion, impact resistance, and film hardness, flexural strength; Anticorrosion evaluation methods: Tafel extrapolation polarization, salt spray methods and EIS; mathematical methods New contributions of the dissertation : The grafted APTS on TiO2 nanotubes were enhanced the corrosion resistance of epoxy coating On the other hand, the steel surfaces were protected by the Zr/Ti/Mo conversion coating that was capable of chromate (VI) ions replacing in the future The composition of the dissertation: The dissertation consists of 112 pages, including 25 tables and 75 photographs Introduction, 05 papers; Conclusions and recommendations, 02 papers; Published works, 01 paper; Reference, 12 papers The main content of the dissertation is divided into three chapters: Chapter Overview, 22 papers; Chapter Methods and experiments, 23 papers and Chapter Results and Discussion, 47 papers CHAPTER OVERVIEW 1.1 Introduction to epoxy coating using APTS-TNTs pigments 1.1.1 Titatnium dioxide nanotubes 1.1.2 Silane coupling agent 1.1.3 Epoxy resin 1.1.4 Overview of research on epoxy coating 1.2 Introduction to conversion coating on steel substrate 1.2.1 Corrosion of metals 1.2.2 Conversion Coating 1.2.3 Overview of research on conversion coating on steel substrate In summary, it can be seen that epoxy resin is one of the most thermoplastic resins in the paint industry, especially epoxy resins from bisphenol A According to the published results, there are many studies about highly anti-corrosion epoxy coating used the grafted-TiO2 nanoparticles by chemical method on their surfaces In addtions, studies have shown that TiO2 nanotubes are more corrosion resistant than nanoparticles However, epoxy coating using TiO2 nanotubes pigments for anticorrosion was not attracted but mainly focus on their photocatalytic effects On the other hand, uncomprehensive published research on the process of producing epoxy coating using APTS-TNTs has been improved corrosion resistance From the above characteristics, it can be seen that the epoxy coating using APTS-TNTs pigment was a potential coating in the anti-corrosion coating Moreover, there are no research has been published on the Zr/Ti/Mo conversion coating, but mainly on single or double-metal conversion coatings with steel protection purposes Therefore, the study of multi-metal Zr/Ti/Mo conversion coating was essential to improve the protection of steel substrate For those reasons, we propose the dissertation : “ Improving corrosion protection of epoxy resin by the modified epoxy and conversion coating on steel substrate” CHAPTER 2: METHODS AND EXPERIMENTS 2.1 Experiment 2.2 Methods - Material analysis methods: X-ray diffraction, scanning electron microscopy, BET, TEM, FTIR, TGA and DSC - Evaluating methods for the mechanical properties of paint film: tape adhesion, impact resistance, and film hardness, flexural strength - Anti-corrosion evaluation methods: Tafel extrapolation polarization, salt spray methods and EIS; mathematical methods - Mathematical methods: experimental planning for level II of Box and Hunter, optimization by the excell-solver program, processing of empirical data CHAPTER 3: RESULTS AND DISCUSSION 3.1 Epoxy coating using APTS-TNTs pigment 3.1.1 Synthesis of Titanium dioxide nanotubes (TNTs) Figure 3.1 XRD patterns of obtained TNTs aggregates calcined at 400, 900 and 1000oC Figure 3.3 TEM images of a) TiO2 nanoparticles before synthesis, b) TiO2 nanotubes , c) TNTs dimension Conclusion 1: Titanium dioxide nanotubes were synthesized via hydrothermal methods from P-25 Degussa TiO2 powders The lengths of these TNTs ranged from 100-150 nm, and the diameter of the tubular materials are almost uniform around 10-15 nm The surface area of TNTs is 188 m2/g at 140oC 3.1.2 APTS-grafted TiO2 nanotubes Figure 3.5 Thermogravimetric analysis of unmodified TNTs (curve (a) and APTS-modified TNTs (curve (b)) Figure 3.9 Chemical grafting of APTS coupling agents onto TNT surfaces Figure 3.10 APTS hydrolysis occurred in the aqueous mixing process Table 3.1 The grafting efficiency of 20 samples with different concentrations, reaction durarions and various temperatures x1 (%KL) x2 (oC) x3 (phút) Eg + + + 5,029 - + + 4,397 + - + 5,687 - - + + + - + - STT 2k 2k x1 (%KL) x2 (oC) x3 (phút) Eg 11 -α 3,795 12 +α 5,475 13 0 -α 3,276 3,670 14 0 +α 4,595 - 4,351 15 0 5,228 + - 3,402 16 0 5,473 - - 4,661 17 0 5,332 - - 2,966 18 0 5,309 STT 2k no -α 0 2,860 19 0 5,329 10 +α 0 5,230 20 0 5,279 Figure 3.11 FTIR spectra of various TNTs: (a) unmodified TNTs and (b) APTS-modified TNTs Figure 3.12 (a) Representative TEM image and (b) highmagnification TEM image with measured withs and lengths of APTSTNTs 11 wt.% APTS-TiO2 nanotubes 10 F 75 wt.% TiO2 nanotubes 10 H 75 wt.% APTS-TiO2 nanotubes 10 H 75 3.1.5 Thermal behavior of epoxy/TNT nanocomposite coating Table 3.5 Summary of TGA results for TiO2 nanotubes/ epoxy nanocomposite coatings and APTS-grafted TiO2 nanotubes/ epoxy nanocomposite coatings at different contents Temp of weight loss Nanocomposite Residual char at 600oC (wt.%) 10 wt.%, 80 wt.% wt.% TiO2 nanotubes 333 434 12.5 wt.% TiO2 nanotubes 337 483 15.5 5wt.% TiO2 nanotubes 336 487 16.7 wt.% TiO2 nanotubes 343 618 20.5 wt.% APTS-grafted TiO2 nanotubes 340 447 14.3 wt.% APTS-grafted TiO2 nanotubes 341 450 16.6 wt.% APTS-grafted TiO2 nanotubes 343 580 19.3 wt.% APTS-grafted TiO2 nanotubes 343 605 20.4 Table 3.6 Summary of Tg results for TiO2 nanotubes/ epoxy nanocomposite coatings and APTS-grafted TiO2 nanotubes/ epoxy nanocomposite coatings at different contents Nanocomposites Epoxy wt.% TiO2 nanotubes wt.% APTS-grafted TiO2 nanotubes wt.% TiO2 nanotubes wt.% APTS-grafted TiO2 nanotubes wt.% TiO2 nanotubes wt.% APTS-grafted TiO2 nanotubes Tg (oC) 105 106 107 108 109 111 111 12 3.1.6 Corrosion resistance of epoxy/(TiO2 nanotubes and APTSgrafted TiO2 nanotubes) composite coating The salt spray test results are shown in Figure 3.22 and detailed summary in Table 3.7 Figure 3.22 Salt spray corrosion test after a) 500 h exposure of epoxy/ wt.% TiO2 nanotubes coating, b) 500h exposure and c) 672h exposure of epoxy/5 wt% APTS-grafted TiO2 nanotubes coating Table 3.7 Corrosion resistance performance of epoxy/ wt.% TiO2 nanotubes coating and epoxy/5 wt% APTS-grafted TiO2 nanotubes coating after time of exposure in salt spray cabinet Samples wt.% TiO2nanotubes wt.% APTS-grafted TiO2 nanotubes wt.% APTS-grafted TiO2 nanotubes wt.% APTS-grafted TiO2 nanotubes Time of exposure (h) 272 272 361 529 Scribe failure rating no (ASTM-D1654) 10 13 Figure 3.23 Barrier mechanism in coating pigmented with TiO2 nanotubes and APTS grafted-TiO2 nanotubes Figure 3.24 shown Nyquist plot for the impedance spectroscope of epoxy/ wt.% TiO2 nanotubes coating and epoxy/5 wt% APTS-grafted TiO2 nanotubes coating Epoxy/ wt.% TiO2nanotubes coating began to appear the second semi-circle, indicated that the erosion of the steel substrate had begun Steel substrates are protected in 59h for epoxy/5 wt% APTS-grafted TiO2 nanotubes coating and 48h for epoxy/ wt.% TiO2 nanotubes coating The test demonstrated that the modified TiO2 nanotubes to the primer could have more positive effect than unmodified ones on the corrosion resistance 14 Figure 3.24 Nyquist plot for the impedance spectroscope of epoxy coating included a) TiO2 nanotubes and b) APTS-TiO2 nanotube in 3.5 wt% NaCl solution Based on the impedance analysis of Figures 3.24, we proposed an equivalent circuit model, as shown in Figure 3.25 15 Figure 3.25 Equivalent circuit modes of epoxy coating/ steel substrate following immersed time 3.1.7 Proposed process for fabricating epoxy/APTS-TiO2 nanotubes coating to improve the corosion resistance of steel substrate Figure 3.27 Process for fabricating epoxy/APTS-TiO2 nanotubes coating 3.2 Conversion coating based on Zr/Ti/Mo compounds 3.2.1 Affecting factors of Ecorr 16 Table 3.9 The Ecorr of 31 samples with different concentrations, pH x1 x2 x3 x4 (g/L) (g/L) (g/L) - -0,40 17 + - - - -0,42 18 +α - + - - -0,39 19 + + - - -0,41 20 - - + - -0,42 + - + - - + + + + - 10 STT Eă.m STT x1 x2 x3 (g/L) (g/L) (g/L) -α 0 x4 Eă.m -0,38 0 -0,39 -α 0 -0,32 +α 0 -0,34 21 0 -α -0,36 -0,43 22 0 +α -0,38 - -0,37 23 0 -α -0,50 + - -0,38 24 0 +α -0,42 - - + -0,32 25 0 0 -0,31 + - - + -0,32 26 0 0 -0,33 11 - + - + -0,39 27 0 0 -0,31 12 + + - + -0,39 28 0 0 -0,32 13 - - + + -0,28 29 0 0 -0,33 14 + - + + -0,24 30 0 0 -0,31 15 - + + + -0,31 31 0 0 -0,32 16 + + + + -0,30 2k 2k no Experiment with optimum conditions, mesured and obtained Ecor = -0,19 (V) as shown in Figure 3.30 This result was the same to the theoretical results (Ecor.th= -0,2 (V)) 17 Figure 3.30 The polarization curves for base steel and Zr/Ti/Motreated steel samples with optimum conditions 3.2.2 Surface morphology and composition Table 3.11 Semiquantitative XRF analysis on intermetallic particles of treated samples (100µm of thinner) Memo Mo Mass (wt.%) 26,9219 Zr 1,7487 Ti 71,3294 The surface structure of Zr/Ti/Mo treated steel was quite special structure compared to the bare steel, showed quite thick flat surfaces 18 Figure 3.33.SEM images of a) untreated sample, c) treated steel surface and EDS spectrum of c) untreated sample, d) treated steel surface 3.2.3 Adhension measurements Tap adhension of Zr/Ti/Mo conversion coating filming of steels were obtained 5B classification due to the edges of the cuts are completely smooth, none of the squares of the lattice is detached The hardness of film was obtained F classification, as shown in Table 2.6 19 Table 3.12 Machenical resistance performance of Zr/Ti/Mo-treated film Samples Flexibility Hardness ( mm) (N) 10 F Zr/Ti/Mo-CC Adhesion Impact (cm) 1050 3.2.4 Corrosion tests Table 3.13 shows the results for salt sprays tests of the untreated/ED coatings and Zr/Ti/MoCC/ED-coatings Figure 3.38 Salt spray corrosion test of untreated- ED coating after (a) 272 h exposure and Zr/Ti/MoCC-ED coating surfaces after (b) 272 h, (c) 361 h and (d) 529 h exposure 20 Figure 3.39 Nyquist plot for the impedance spectroscope of a) photphate coating and b) photphate coating after 30 days in 3.5 wt.% NaCl solution Figure 3.40 Nyquist plot for the impedance spectroscope of a) Zr/Ti/MoCC-ED coating and b) Zr/Ti/MoCC-ED coating after 31 days c) Zr/Ti/MoCC-ED coating after 32 days in 3.5 wt% NaCl solution 21 Table 3.13 Corrosion resistance performance of untreated-ED coating and Zr/Ti/MoCC-ED coating on JISG 3141 substrates after time of exposure in salt spray cabinet Time of exposure Scribe failure rating Untreated/ED coating (h) 272 no (ASTM-D1654) Zr/Ti/MoCC-ED coating 272 10 Zr/Ti/MoCC-ED coating 361 Zr/Ti/MoCC-ED coating 529 Samples Figure 3.40 Equivalent circuit modes of Zr/Ti/MoCC-ED coating/ steel substrate following immersed time 3.2.5 Proposed process for fabricating Zr/Ti/MoCC-ED coating to improve the corosion resistance of steel substrate 22 Figure 3.41 Process for fabricating Zr/Ti/MoCC-ED coating CONCLUSION A Conclusion: After the implementation process, the dissertation has achieved some results The APTS-grafted TiO2 nanotubes/ epoxy nanocomposite showed better corrosion resistance than TiO2 nanotubes/ epoxy nanocomposite Standing 672 h exposure, the corrosion resistance of epoxy resin greatly improved by using reinforcing the APTSmodified TNTs 23 Titanium dioxide nanotubes (TNTs) were surface-modified with 3-aminopropyl triethoxysilane (APTS) by an aqueous process at reaction conditions: 190 wt.% APTS/TNTs, 70oC and 337 mins in this study The lengths of these APTS-TNTs ranged from 100-150 nm, the diameter of the tubular materials are almost uniform around 10-15 nm, anatase crystalline phases and the surface area 188 m2/g The dispersion capacity of APTS- TiO2 nanotubes in toluene solvent and in epoxy were better than TiO2 nanotubes because the amin groups on the modified TiO2 nanotubes interacted with epoxy groups of the epoxy D.E.H.24 The results showed that surface treatment of TiO2 nanotubes with APTS improves the impact resistance and bending resistance of epoxy coating, but unchanged hardness than unmodified- TiO2 nanotubes.The obtained results shown the thermal stability of APTSgrafted TiO2 nanotubes/ epoxy nanocomposite was higher compared to that of the TiO2nanotubes/ epoxy nanocomposite Zr/Ti/Mo conversion coating could significantly improve the corrosion protection properties of the ED coating even at long immersion times Scanning electron microscopy with energydispersive X-ray spectroscopy (SEM/EDX) has indicated the surface structure and the presence of Mo/Zr/Ti on surface of the steel Passivation layer containing Zr, Ti and Mo has been successfully carried out on steel by dipping in solution of 17 g/L Na2MoO4, g/L K2ZrF6, g/L H2TiF6 and pH = 5.The corrosion potential and current of coating in case of with and without passivation layer on the steels was determined by potentiodynamic polarization test, showed that the corrosion current density decreased when using Zr/Ti/Mo coating 24 B Contribution of the dissertation Proposed process for fabricating epoxy/APTS- TiO2 nanotubes coating to improve the corosion resistance of steel substrate Proposed process for fabricating Zr/Ti/MoCC-ED coating to improve the corosion resistance of steel substrate C Recommendations The APTS- TiO2 nanotube/epoxy coating was synthesized and researched at the Polymer Chemistry Laboratory This system should expand the application market or technology transfer On the other hand, the research of self-cleaning paint system, solar cells… should continue to invest in the future The Zr/Ti/Mo conversion coating could significantly improve the corrosion protection properties of the ED coating However, the mechanism of multilayer metal deposition of Zr/Ti/Mo on steel substrate has not been studied It is necessary to study this mechanism in order to have appropriate adjustment to more improve the corrostion protection of steels PUBLICATIONS Duong Thi Hong Phan, Le Minh Duc, Dao Hung Cuong, Synthesis and mechnical properties of (3-aminopropyl triethoxysilane) grafted TiO2 – epoxy nanocomposites, Vietnam Journal of Chemistry, 4E2355, 272-277 (2017) 2.Duong Thi Hong Phan, Le Minh Duc, Dao Hung Cuong, Modification of TiO2 nanotubes with organic silane for high anticorrosion of epoxy coating, Vietnam Journal of Chemistry, 5E3455, 405-410 (2017) 3.Duong Thi Hong Phan, Le Minh Duc, Dao Hung Cuong, Protection of steel JISG 3141 with chromium-free conversion coating based on inorganic salt (Zr/Ti/Mo), Journal of Science and Technology, vol.55 (5B), 57-65 (2017) Duong Thi Hong Phan, Le Minh Duc, Dao Hung Cuong, Corrosion resistance and mechanical properties of TiO2 nanotubes / epoxy coating on steel SPCC-JISG 3141, Journal of Science and Technology, vol.55 (5B), 203-209 (2017) Duong Thi Hong Phan, Nguyen Tien Dung, Le Minh Duc, Dao Hung Cuong, Corrosion inhibition of steel by chromium-free conversion coating depended on inorganic (Mo/Zr/Ti), Journal of Science and Technology, The University of DaNang, 07(116), 6266 (2017) Hong Phan Duong, Minh Duc Le, Hung Cuong Dao and ChiaYun, Surface modification of TiO2 nanotubes by grafting with APTS coupling agents, Mater.Res.Express, Vol 4:105043, 1-9 (2017), (SCIE, IF 1.068) Hong Phan Duong, Chia-Hsiang Hung, Hung Cuong Dao, Minh Duc Le and Chia-Yun Chen, Modification of TiO2 nanotubes with 3aminopropyl triethoxysilane and its performances in nanocomposite, New J Chem, Vol.42 , 8745-8751 (2018), (SCI, IF 3.269 ... into epoxy resin Figure 3.14 Schematic of the structure of the grafted TNTs /epoxy resin 10 Figure 3.15 FTIR spectra of a) TiO2 nanotubes /epoxy coating and b) APTS-grafted TiO2 nanotubes /epoxy. .. APTS-grafted TiO2 nanotubes/ epoxy nanocomposite showed better corrosion resistance than TiO2 nanotubes/ epoxy nanocomposite Standing 672 h exposure, the corrosion resistance of epoxy resin greatly improved... nanotubes in toluene solvent and in epoxy were better than TiO2 nanotubes because the amin groups on the modified TiO2 nanotubes interacted with epoxy groups of the epoxy D.E.H.24 The results showed