The thesis aims to investigate and select suitable conditions for synthesis of Nanocompozit Silica / Polypyrol by In-situ method. Nature and study of corrosion inhibition ability of Silica / Polypyrol carbon steel. Select suitable conditions for synthesis of silica / Polypyrol anionic doped for In-situ method. Corrosion inhibitory ability for Nanocompozit Silica / Polypyrol-Anion Carbon steel for polybutyral coating. Corrosion protection for carbon steel of epoxy coating containing SiO2 / polypyrol-anion composite.
VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY …… ….***………… VU THI HAI VAN Project name: SYNTHESIS AND CHARACTERIZATION OF SILICA/POLYPYRROLE NANOCOMPOSITE ORIENTED FOR USE IN ORGANIC CORROSION PROTECTION COATING Major: Theoretical chemistry and Physical chemistry Code: 9440119 SUMMARY OF CHEMICAL DOCTORAL THESIS Hanoi – 2018 The thesis was completed at: Graduate University of Science and Technology - Vietnam Academy of Science and Technology Scientific Supervisors: Assoc Prof Dr., To Thi Xuan Hang Assoc Prof Dr Dinh Thi Mai Thanh Referee 1: Referee 2: Referee 3: The thesis will be defended in front of doctoral thesis judgement, held at ……….…, … The thesis can be found at: - Library of Graduate University of Science and Technology - National library of Vietnam A INTRODUCTION The necessity of the research Nanocomposite material has a wide range of applications in various areas including metal corrosion protection There are many methods of corrosion protection, but the simple, low cost and easy to apply method is organic protection coating Chromat is a highly effective corrosion inhibitor pigment in organic coatings, however it is highly toxic, which causes cancer, so countries around the world have gradually eliminated chromates and research into environmental friendly - corrosion inhibitors Corrosion inhibiting and metal protection properties of conductive polymers were first investigated by Mengoli in 1981 and DeBery in 1985, respectively Studies have shown that polymer films formed on metal surfaces have high adhesion and good protection, however, this method has limitations on the size of the material to be protected Therefore, recent studies have focused on the use of conductive polymers as corrosion inhibitors in organic coatings This coating shows the advantages of conducting polymer overcomes the difficulties of film forming These studies focus on two of the most popular and important conductive polymers: polypyrrole (PPy) and polyaniline for corrosion protection of iron / steel Compared to polyaniline, PPy shows high electrical conductivity in both acidic and neutral environments, so it can be widely used in various fields such as energy storage devices, bio-sensors, materials photoelectric, anticorrosion coating In addition, the synthesis of PPy films on metal substrates is easier due to the low oxidation potential of PPy Moreover, PPy is able to stabilize better than polyaniline However, PPy has low dispersibility, so the combination with nano additives to form nanocomposite is very interested in research Silica nanoparticles (SiO2) have high surface area, good dispersion, ease of preparation so the use nanosilica can improve the expansion; sound insulation; flexural strength; tensile strength; and corrosion protection performance The PPy's conductivity as well as the ability of the ion-selective redox reaction greatly depends on the nature of the polymer and the synthesis conditions In addition, when corrosion occurs, PPy is capable of exchanging anions, so that the counter ions in the polymer also play an important role in the anticorrosion ability Counter anions, which is small in size and highly flexible, will easily be released from the polymer network While larger size anions can reduce bond length, leading to the increase of conductivity and solubility Therefore, synthesis of silica/polypyrol nanocomposite and silica/polypyrol-counter anions is a promising topic, using the advantages of PPy, silica as well as anionic component There are some studies subjecting the use of of PPy, PPy-anion, PPy/inorganic oxide However, there is no study about silica/polypyrrole nanocomposite as well as silica/polypyrrole exchanged counter anions and its application in organic coatings for anticorrosion Therefore, the thesis "Synthesis and characterization of silica/polypyrrole nanocomposite oriented for use in organic corrosion protection coatings" is needed, contributing to the synthesis and application of silica/polypyrrole nanocomposite in the field of corrosion protection The main contents and objectives of the thesis - Investigation of the synthesis parameters of silica/polypyrrole and silica/polypyrrole-doped anions nanocomposite by in-situ method - Characterization and corrosion inhibitor abilities of silica/polypyrrole nanocomposites for carbon steel - Evaluation of corrosion protection for carbon steel of polyvinylbutyral and epoxy coatings containing silica/polypyrrole-doped anions 3 The scientific significance, practicality and new contributions of the thesis - Silica/polypyrrole nanocomposites were synthesized by in-situ method in the presence of doped anions, such as: dodecyl sulfate, benzoate and oxalate The synthesize nanocomposites have spherical structure, diameter in the range of 50-150 nm Nanocomposite contains the oxalate anion showed the best inhibitor ability in polivinylbutyral coatings - The potential application of silica/polypyrrole-doped oxalate nanocomposite in epoxy coatings has been evaluated for corrosion protection The results were obtained by electrochemical methods showed that silica/polypyrrole-doped oxalate nanocomposite significantly improved corrosion resistance of epoxy coating The results open up the prospect of using silica/polypyrrole-doped oxalate nanocomposite as a corrosion inhibitor in organic coatings Structure of the thesis The thesis includes 127 pages: introduction (3 pages), the overview (35 pages), experimental (13 pages), results and discussions (60 pages), conclusion (1 page) , new contributions of the thesis (1 page), list of published scientific works (1 page), tables, 63 images and graphs, 141 references B CONTENT OF THE THESIS CHAPTER I OVERVIEW The thesis has summarized literature over the world about synthesis of silica, polypyrrole, silica/polypyrrole composites and its application, special in anticorrosion CHAPTER II EXPERIMENTAL 2.1 Materials - Pyrrole, C4H5N, (97 %, Germany); TEOS, Si(OC2H5)4, (South Korea); PVB, (C8H14O2)n, (Japan) - HCl, FeCl3, Na2C2O4, CH3(CH2)11OSO3Na, NaC6H5CO2, C3H6O, CH4O (China) - Epoxy bisphenol A, Epotec YD011-X75 and Polyamide 307D-60 (South Korea) 2.2 Synthesis of silica/polypyrrole nanocomposites 2.2.1 Silica TEOS was dropped slowly into 140 ml HCl solution with pH = The mixture was stirred for 24 hours at room temperature, and then was heated at 80oC during 24 hours The precipitate was washed with distilled water to pH = and dried at 80oC for 24 hours in a vacuum oven 2.2.2 Silica/polypyrrole nanocomposites Prepared three solutions: - Solution 1: SiO2 were dispersed in 40 ml H2O or C2H5OH by ultra-sonic in 30 minutes - Solution 2: mmol pyrrole were dispersed in 20 ml H2O - Solution 3: 0.05 mol FeCl3.6H2O were dissolved in 40 ml H2O or C2H5OH Solution was dropped slowly into solution 1, stirred for hour Then solution was dropped slowly into above mixture, stirred for 24 hours The mixture was filtered and washed times with distilled water and once with mixture of methanol and acetone to remove unwanted products The precipitate was dried at 80oC in 24 hours in vacuum oven To synthesis SiO2/PPy-doped anions, follow the same process, only additional of 2.5 mmol NaC2O4 (Ox) or NaC12H25SO4 (DoS) or C7H5NaO2 (Bz) in solution 2.2.3 Synthesis polyvinylbutyral coatings containing SiO2/PPy nanocomposites Step 1: Carbon steel sheets were used as substrate (10×5×0.2 cm) The sheets were cleaned with soap, distilled water and ethanol, dried and marked Then the sheets were polished with abrasive paper 600 grades, washed by distilled water, ethanol and dried Step 2: PVB solution was prepared by dissolving 10 wt% of PVB in mixture of propanol and ethanol (ratio 1:1) The SiO2/PPy nanocomposites were dispered into PVB solution by continuous magnetic stirring and sonication for hours Step 3: The liquid paints were deposited on the bare steel using a spin-coater at rotating speeds up to 600 rpm Finally, all samples were dried at ambient temperature for days The dry films thickness is about 11±2 µm (measured by Minitest 600 Erichen) 2.2.4 Synthesis epoxy coatings containing SiO2/PPy nanocomposites The synthesize process is similar, epoxy solutions were prepared by dispersed wt% SiO2/PPy nanocomposites into epoxy and xylene by magnetic stirring The epoxy coatings containing SP, SPO1, SPO2 and SPO3 were labeled as ESP, ESPO1, ESPO2 and ESPO3, respectively The rotating speed is 1000 rpm due to the high viscosity of epoxy solutions The dry films thickness is about 25±2 µm (measured by Minitest 600 Erichen) 2.3 Methods - IR, SEM, TEM, EDX, UV-Vis were measured at Institute for Tropical technology, National Institute Of Hygiene And Epidemiology and Future Industry Institute - TGA were performed with a heating rate of 10oC per minute, from 25-850oC, in air, at Future Industry Institute - X-ray diffractometer were carried out with scanning rate 0.03° per second and theta (2θ) angle ranging from 10° to 80° at current 40.0 mA and voltage 40.0 kV, at Future Industry Institute - XPS were measured at Future Industry Institute using X-radiations with Al at 15 kV- 15 mA - The conductivities were measured by cyclic voltammetry method through the two-point-electrode without electrolyte with sample thickness is cm and sample area is cm2 - Open circuit potential and electrochemical impedance spectra were measured at Institute for Tropical technology - Salt spray test was carried out followed by ASTM B117 standard at Institute for Frontier Materials CHAPTER III RESULTS AND DISCUSSIONS 3.1 Synthesis and characterization of SiO2/PPy nanocomposties 3.1.1 Effect of synthesis solution Synthesis solution plays an important role in dispersive ability, morphology and characterization of SiO2/PPy nanocomposites There were some studies reported that the presence of ancol can improve the dispersion and modify surface characteristic of silica Therefore, SiO2/PPy nanocomposites were synthesized in solution containing water, mixture of ethanol: water = 2:3 and mixture of ethanol : water = 4:1, labeled as SiO2/PPy-W, SiO2/PPy-EW and SiO2/PPy-E, respectively IR spectra (Figure 3.1) of SiO2/PPy-W, SiO2/PPy-E and SiO2/PPy-EW showed similar trend, included characteristic bands of SiO2 (~471, 794 and 1080 cm-1) and PPy (~1530, 1450, 1405 and 1050 cm-1) EDX results of SiO2/PPy-W, SiO2/PPy-E and SiO2/PPy-EW are shown in figure 3.2 The spectra show pic of silicon and oxygen, which is from silica; carbon, nitrogen and chloride, which is from polypyrrole Weight percentages of silicon increase from 20.18 to 21.07 and 22.08% with SiO2/PPy-W, SiO2/PPy-E and SiO2/PPy-EW, respectively Figure 3.1 FT-IR spectra of SiO2, PPy and SiO2/PPy nanocomposites Figure 3.2 EDX diagrams of SiO2, PPy and SiO2/PPy nanocomposites SEM photographs of synthesized SiO2 and SiO2/PPy nanocomposites are shown in figure 3.3 The synthesized nanocomposites have similar morphology with spherical shape Diameter of nanocomposites is higher than silica It can be explained by the deposition of pyrrole on the silica surface, the polymerization of pyrrole in the presence of oxidation agent Figure 3.3 SEM photographs of SiO2 (a), SiO2/PPy-W (b), SiO2/PPy-EW (c) and SiO2/PPy-E (d) Figure 3.5 shows UV-Vis spectra of SiO2, PPy SiO2/PPy-W, SiO2/PPy-E and SiO2/PPy-EW Characteristic peak of silica is observed at 300 nm In the case of PPy, there are two main peak, at 400-450 nm and broad peak at 900-1100 nm The first peak at low wavelength is presented for band gap of π-π* bond In the other hand, this peak also confirms the bipolarons state of PPy Peak at higher wavelength is characterized for conductive electron In comparison between spectra of PPy and nanocompositess, there is the change of peak position to higher wavelength zone This result indicated the longer conjugated bond, corresponding with the higher conductivity Figure 3.5 UV-Vis spectra of samples Figure 3.6 CV diagram of samples The electrical conductivities of samples were determined through CV-diagrams from figure 3.6 PPy has the highest conductivity, 0.432 S.cm-1 The conductivities of nanocomposites synthesized in water, ethanol:water = 2:3 and ethanol:water = 4:1 is 0.19, 0.14 and 0.11 S.cm-1, respectively It can be explained by the insulation of silica Figure 3.7 showed the survey scans of PPy, SiO2/PPy-W, SiO2/PPy-EW and SiO2/PPy-E PPy spectra showed characteristic peak of carbon C1s, nitrogen N1s and clo Cl2p, in agreement with EDX results In comparison with PPy, XPS spectra of nanocomposites have two more peak, at 101.9 eV and 531.5 eV, represented for silicon Si2p and oxygen O1s These results indicated the presence of silica in nanocomposites With PPy, the high resolution spectra included four components (figure 3.8) At the lowest bonding energy and highest intensity, the main peak at 285.1 eV, represented for C-C bond between Cα and Cβ in pyrrole ring Peak at 286.2 eV; 287.8 eV and 290.4 eV indicated PPy at doped state Peak presented for C=N and =C-NH•+ (polaron) bond is observed at 286.2 eV The peak at 287.8 eV is assigned to –C=N+ bond of bipolaron PPy Figure 3.7 XPS spectra of PPy, SiO2/PPy-W, SiO2/PPy-EW and SiO2/PPy-E With N (1s) high resolution spectrum showed three components (figure 3.9) The signal at 399.6 eV was assigned to the –NH group of pyrrole ring At higher bonding energy, there were two peak which assigned to pyrrole at doped state Peaks at 400.5 eV and 402.4 eV were assigned to NH•+ of polaron PPy and =NH+ of bipolaron PPy, respectively Figure 3.8 High resolution C1s and N1s of PPy Figure 3.9 High resolution C1s and N1s of SiO2/PPy-W The high resolution C1s and N1s spectra of SiO2/PPy-W, SiO2/PPy-EW and SiO2/PPy-E nanocomposite were shown in figure 3.9, 3.10 and 3.11, respectively All the spectra showed similar trend with PPy However, the bonding energy of nanocomposites is lower than that of PPy This result indicated the decrease of conjugated bond length, according to the lower conductivity, in agreement with conductivity measurement From the analysis of XPS spectra, the weight percentages of each element and oxidation state of nitrogen were listed in table 3.3 The results indicated that when change the synthesis solution, weight percentage of element insignificant changed Percentages of nitrogen at neutralize and polaron state were higher than that of nanocomposites It showed the higher oxidative ability Therfore, the percentages of nitrogen at bipolaron state are higher, the lower conductivities Figure 3.10 High resolution C1s and N1s of Figure 3.11 High resolution C1s and N1s of SiO2/PPy-EW Bảng 3.3 Analysis Sample PPy SiO2/PPy-W SiO2/PPy-EW SiO2/PPy-E C 74,5 35,7 35,4 34,5 SiO2/PPy-E parameter from XPS spectra Weigh percentage (%) N O Si 23,6 7,8 32,6 22,4 7,5 32,5 23,3 7,7 32,6 23,8 Cl 1,9 1,5 1,3 1,4 Oxidation state (%) -N = -NH-N+ 0,08 0,65 0,27 0,17 0,58 0,25 0,21 0,55 0,24 0,24 0,51 0,25 + 3.1.1 Effect of pyrrole/silica ratio The quantities of silica showed important affect to the formation of nanocomposites Therefore, in this study, SiO2/PPy nanocomposites were synthesized at constant quantity of PPy and silica changed from 2,5 mmol (SP1); mmol (SP2); 7,5 mmol (SP3) to 10 mmol (SP4) The ratio of pyrrole/silica changed from 0.4, 0.2, 0.13 to 0.1, respectively Figure 3.12 IR spectra of SiO2, PPy, SP1, SP2, SP3 and SP4 Figure 3.13 EDX spectra of SiO2, PPy, SP1, SP2, SP3 and SP4 IR spectra of nanocomposites showed characteristic peak of silica (1080, 793 and 471 cm-1) and polypyrolle (1530 and 1450 cm-1) (figure 3.12) Its indicated the presence of silica in nanocomposites With SP1, the quantity of silica is low, therefore, the characteristic peaks had lower intensity when peak of PPy had higher intensity When silica percentage is increase, from SP2 to SP4, IR spectra showed strong peak of silica at 1080 cm-1 EDX results showed four main elements in nanocomposites: carbon, nitrogen, oxygen and silicon (figure 3.13) When the quantity of silica in synthesized solution increase, the weight percentage of silicon in nanocomposites increase, from 20.48 to 21.19, 25.03 and 28.14%, in SP1,SP2, SP3 and SP4, respectively SEM photographs of silica, SP1, SP2, SP3 and SP4 were shown in figure 3.14 All the samples had spherical shapes When forming nanocomposites, diameter of sample was increase Moreover, when the quantity of silica increased, the particles sizes also increased It might due to the polymerization of PPy, cover silica shell Figure 3.14 SEM photographs of SiO2 (a), SP1 (b), SP2 (c), SP3 (d) and SP4 (e) Figure 3.15 TGA diagrams of PPy, SP1, SP2, SP3 and SP4 Figure 3.15 showed TGA diagrams of samples With SP1, SP2, SP3 and SP4, TGA diagrams had same trend, the weight loss was 48.5, 42.2, 38.1 and 32%, respectively TGA diagrams consisted of two stages: an initial weight loss at less than 100 oC due to the loss of water absorption in the surface The second loss from 100-650oC might due to the degradation of polypyrrole blackbone and the decomposition of oxidation agent However, the total weight loss of nanocomposites was lower than that of PPy It can be explained by the high thermal resistance of silica Calculated from TGA results, weight percentage of silica in SP1, SP2, SP3 and SP4 is 51, 57, 61 and 67% 3.1.2 Electrochemical characteristic of SiO2/PPy nanocomposites 3.1.3.1 Inhibitive ability in NaCl 3% solution Figure 3.16 showed the open circuit potential of carbon steel immerse in NaCl 3% include and not include g/L SP1, SP2, SP3 and SP4 nanocomposites after 36 hours Initially, for bare steel, OCP value reached -0.6 VSCE, then decreased over time After 20 hours of immersion, OCP value is -0.7 VSCE, and kept stably The decrease of OCP can be explained by the erosion formation After 36 hours of immersion, the OCP value of bare steel was -0.7 VSCE, reaching the corrosion potential of steel In the case of SP1, SP2, SP3 and SP4, OCP varied with the same trend In the beginning, it reached -0.32, -0.32, -0.37 and -0.40 VSCE, respectively These results showed that SiO2/PPy nanocomposites can shift the OCP of steel to passive region, which is demonstrated the role of anodic inhibitor Over time, the value of OCP dropped toward negative value, however, always positive than that of bare steel Therefore, SiO2/PPy showed good inhibitive ability, but it decreased overtime due to the erosion of corrosive agents After 36 hours of immersion, the OCP of SP1, SP2, SP3 and SP4 were -0.63, -0.64, -0.68 and -0.68 VSCE, respectively 10 Figure 3.19 Bode diagrams of PVB-SP1, PVB-SP2, PVB-SP3 and PVB-SP4 after immersion time in 3% NaCl solution: 10 minutes (□), 10 hours (○), 36 hours (Δ) Bode impedance spectra of steel coated with PVB and PVB containing 10 wt% nanocomposites were shown in figure 3.19 For PVB coating containing SiO2/PPy nanocomposites, modulus value at the intial time was higher than that of PVB, it might due to the presence of SiO2/PPy can increase the barrier protection Impedance decreased after 10 hours of immersion, however, up to 36 hours, impedence slightly decresed with samples This results were explained by the dual protection of nanocomposites First, silica exhibited shielding capablities The presence of silica in the organic coating prevents the connection between polymer network, therefore causing the low diffusion rate of oxygen, hydrogen and corrosive ions In the other words, erosive ions needed longer time to diffuse, attack to the interface between polymer coating and metal surface to create the corrosive reactions 3.2 Doped SiO2/PPy nanocomposites Many studies have shown that PPy doped with anions such as molybdate, oxalate, dodecyl sulfate, benzoate have corrosion protection ability for metals in chloride solution PPy can passivate metals, however, after time, when the PPy is completely reduced, PPy will lose its protection ability At this point, doped anions can be released, which is capable of reintroducing metal With the small doped anions, such as oxalate, it is easy to be released from polymer, forming complexes with metals, filling the corrosive sites With large doped anions, such as benzoate or dodecyl sulfate, the flexibility is poorer but it can limit the penetration of chloride ions into the coating Thus, the effects of different sizes - doped anions on characterization and corrosion protection performance have been investigated 3.2.1 Characterization of SiO2/PPy-doped nanocomposites SiO2/PPy nanocomposites is synthesized in aqueous solution, 2.5 mmol SiO2, mmol Py and 2.5 mmol NaC2O4 (Ox) or NaC12H25SO4 (DoS) or C7H5NaO2 (Bz) Figure 3.21 showed the infrared spectrum of SiO2, PPy SiO2/PPyDoS, SiO2/PPyOx and SiO2/PPyBz For nanocomposite containing dodecylsulfate anion, peak at 1527 cm -1 represented for 13 C-C bond and at 1435 cm-1 represented for C-N bond In addition, S=O and Si-O-Si were defined at 1170 and 1080 cm-1, respectively With pure sodium sulfate, characteristic peak of S=O bond was determined at 1176 cm-1, the insignificantly shift of the wavelength was explained by the binding of PPy and dodecyl sulfate anion The IR spectrum of SiO2/PPyBz showed a slightly shift of characteristic peak of silica and polypyrrole with no other peak Figure 3.21 IR spectra of SiO2 (a), PPy (b), SiO2/PPyDoS (c), SiO2/PPyOx (d) and SiO2/PPyBz (e) Figure 3.22 SEM photographs of SiO2/PPy (a), SiO2/PPyDoS (b), SiO2/PPyOx (c) and SiO2/PPyBz (d) IR spectrum of SiO2/PPyOx showed the characteristic peak of PPy and SiO2 Peak at 1530, 1440 and 1075 cm-1 were assigned to C-C, C-N and Si-O-Si bond, respectively The slightly shift of these peak to lower wavelength might due to the bonding between silica and polypyrrole via hydrogen bond In addition, the characteristic peak of oxalate anion, C=O bond was found at 1670 and 1710 cm-1 O-C=O bond at 1440 cm-1 was overlapped by C-N bond of PPy These peaks had a slightly shift compared to peaks of pure sodium oxalate (1416 1633cm-1) The IR results confirmed the presence of doped anions in nanocomposites Figure 3.22 a, b, c and d showed SEM photographs of SiO2/PPy, SiO2/PPyDoS, SiO2/PPyOx and SiO2/PPyBz All samples were spherical, diameter of SiO2/PPyDoS, SiO2/PPyBz and SiO2/PPyOx is higher than that of pure silica, which may be due to the absorption of monomer pyrrole on silica surface in the presence of FeCl3, increasing the particle size The element composititon of SiO2/PPyDoS, SiO2/PPyOx and SiO2/PPyBz was determined by EDX, the results were shown in Table 3.7 The main components of nanocomposites were carbon, nitrogen, chlorine (from PPy); oxygen and silicon (from silica), sulfur from dodecyl sulfate anion 14 Figure 3.23 EDX diagrams of samples Figure 3.25 TGA diagrams of samples Figure 3.25 showed TGA diagrams of SiO2/PPy, SiO2/PpyDoS, SiO2/PpyOx and SiO2/PpyBz nanocomposites The weight loss occurred in stage with the total weight loss of SiO2/PPy, SiO2/PpyDoS, SiO2/PpyOx and SiO2/PpyBz was 39%, 52%, 58% and 59% at 850oC, respectively The total weight loss of SiO2/PpyOx was higher than that of SiO2/PpyDoS, it might due to the decomposition temparature of silica is 1000oC, therefore, when silica content in SiO2/PpyDoS is higher, the total weight loss is lower, this results was in agreement with EDX results The same explaination can be used with SiO2/PpyBz, the total weight loss is higher due to the easy decomposite components such as carbon, oxygen, nitrogen in nanocomposite were higher Table 3.7 EDX datas of SiO2/PPyOx, SiO2/PPyDoS and SiO2/PPyBz nanocomposites wt% Samples C O N Si S Cl SiO2/PPyOx 39.68 31.43 8.41 20.47 0.00 0.01 SiO2/PPyDoS 39.73 28.94 7.05 21.14 3.19 0.05 SiO2/PPyBz 40.05 30.35 9.35 20.23 0.00 0.02 The conductivity of PPy, SiO2/PPy, SiO2/PPyOx, SiO2/PPyBz and SiO2/PPyDoS were evaluated by CV diagrams (figure 3.26) The conductivity of Py, SiO2/PPy, SiO2/PPyOx, SiO2/PPyDoS and SiO2/PPyBz was 0.287; 0.109; 0.101 and 0,105 S/cm, respectively The decrease of conductivity can be explained by the size of doped anions Dodecyl sulfate and benzoate anions had large size, with low mobility, reducing the mobility of free electron in PPy molecule, resulting in reduced conductivity Additional, the lower percentage of PPy in nanocomposites and the insulation of silica also reduced the conductivity of nanocomposites Figure 3.26 CV diagrams of samples Figure 3.27 XPS spectra of samples Figure 3.27 showed the XPS spectra of SiO2/PPyOx, SiO2/PPyDoS and SiO2/PPyBz at wide binding energy The results showed that all samples had characteristic peak of carbon C 1s nitrogen N1s and chloride Cl2p (from PPy), oxygen O1s and silicon Si2p (from SiO2) Besides, with SiO2/PPyDoS, there was peak at 167,3 eV, represented for sulfur S2p Spectra of O1s SiO2/PPyOx, SiO2/PPyDoS and SiO2/PPyBz nanocomposites were shown in figure 3.28 With SiO2/PPyOx and SiO2/PPyBz, O1s spectra included two peak, representing for O=C-O bond (at 531,3 and 531,2 eV) and –OH bond (at 533,8 and 533,7 eV) The presence of these peaks confirmed the presence of – COOH group of oxalate and benzoate anions With SiO2/PPyDoS, there was the third peak, representing for O=S bond at 531.6 eV Characteristic peak of O=C-O and –OH group slightly shift 15 to 531.0 and 533.6 eV Figure 3.29 showed the N1s spectra of SiO2/PPyOx, SiO2/PPyDoS and SiO2/PPyBz The spectra had the same trend, with three peaks were assigned to neutralized nitrogen, polaron and bipolaron Figure 3.28 O1s spectra nanocomposites of SiO2/PPyOx, SiO2/PPyDoS and SiO2/PPyBz It can be seen from above results that the characteristic peaks in SiO2/PPyOx showed the higher binding energy than that of SiO2/PPyDoS and SiO2/PPyBz, indicating the longer conjugate link in polymer, representing for higher conductivity, in agreement with conductivity measurement Figure 3.29 N1s spectra of SiO2/PPyOx, SiO2/PPyDoS and SiO2/PPyBz nanocomposites 3.2.2 Effects of SiO2/PPy-doped nanocomposites to PVB coatings 3.2.2.1 Open circuit potential Figure 3.30 showed the variation of open circuit potential of coated carbon steel with PVB and PVB containing 10 wt% SiO2/PPy, SiO2/PPyDoS, SiO2/PPyOx after 36 hours of immersion in 3% NaCl solution Initially, OCP of carbon steel coated with PVB reached -0.5 VSCE, then potential dropped toward negative zone after hours The decrease of potential can be explained by the following way: chloride ions attack the coatings therefore the barrier protection decrease, leading to the decrease of potentials After hours of immersion, the OCP values maintained at corrosion potential of carbon steel The OCP value of carbon steel coated with PVB coating reached -0.67 VSCE after 36 hours 16 Figure 3.30 OCP values of carbon steel coated with PVB (a) and PVB containing 10 wt% SiO2/PPy (b), SiO2/PPyOx (c), SiO2/PPyDoS(d) and SiO2/PPyBz (e) after 36 hours of immersion in NaCl solution With carbon steel coated with PVB containing 10 wt% SiO2/PPy, in the beginning, the potential was -0.2 VSCE, indicating the presence of nanocomposites can shift the OCP to anode zone After this, potential tend to shift to negative zone due to the diffusion of aggressive ions and the degradation of barrier protection After 10 hours of immersion, OCP value was stable, at ~ -0.35 VSCE It can be explained by the effects of PPy to carbon PPy can “self healing”, oxidation carbon surface at the corrosion point, keeping carbon at passivate stage After 30 hours of immersion, potential continuously shift to negative zone, indicating the decrease of protective abilities of PPy OCP value of carbon steel coated by PVB containing SiO2/PPy reached -0.4 VSCE after 36 hours of immersion In the case of carbon steel coated with PVB containing SiO2/PPyOx, SiO2/PPyDoS and SiO2/PPyBz, the initially potentials were -0.01 VSCE; -0.05 VSCE and -0.07 VSCE, respectively This result indicated the important role of doped anions in the improvement of anticorrosion Dodecyl sulfate and benzoate, with the large size, show the low mobility, therefore difficultly to be released from PPy On the other hand, oxalate anion with small size, easy to be released, forming complex with ferric ions, increasing the anticorrosion ability Consequence, SiO2/PPyOx nanocomposites showed the best corrosion protection performance 3.2.2.2 Electrochemical Impedance Spectroscopy Bode diagrams of steel coated with PVB, PVB containing 10 wt% SiO2/PPy, SiO2/PPyBz, SiO2/PPyDoS and SiO2/PPyOx after hour of immersion in 3% NaCl solution were shown in Figure 3.31 In the low frequency range from 0,01Hz to 1Hz, the modulus impedance of steel coated with PVB was approximamtely times higher than that of steel coated with PVB At Hz, the modulus impedance of PVB-SiO2/PPyBz, PVB-SiO2/PPyDoS and PVB-SiO2/PPyOx reached 1.71×106; 1.19×106 and 3.64×106 Ω.cm-2, about 30 times higher than that of PVB-SiO2/PPy (6,28×104 Ω.cm-2) Impedance at this frequency region characterizes the corrosion process at the interface between coating and steel surface The high impedance at this region confirms the presence of doped anions can improve the protection performance of PVB coating in sodium chloride solution In addition, from the frequency of 10Hz, impedance paths of PVB-SiO2/PPyBz, PVB-SiO2/PPyDoS and PVB-SiO2/PPyOx were linear, confirming the good coverage of the coating From the diagrams, its shown that all the samples existed only single phase, corresponding 17 to the erosion occurring on the surface of coating These results indicated that ater one hour of immersion, NaCl solution had not penetrated into the coating Figure 3.31 Bode diagrams of carbon steel coated with PVB and PVB containing nanocomposites after hour of immersion After 24 hours of immersion (Figure 3.33), the impedance maintained linear at high frequency region However, at low frequency region, 10 mHz, the impedance value of PVB-SiO2/PPyDoS, PVB-SiO2/PPyBz and PVB-SiO2/PPyOx decreased to 3.34×104; 3.34×104 and 4.27×104 Ω.cm-2 The phase values of SiO2/PPyDoS and PVB-SiO2/PPyBz contained two phase components, indicating a reduction in the protective ability of the coatings In the case of PVB-SiO2/PPyOx, impedance value kept stably at high value and phase diagram contained only one phase component after 24 hours of immersion, confirming the good barrier protection It can be seen that the protection performance of PVB containing SiO2/PPy was improved in the presence of doped anions By forming an oxidation – reduction pair between PPy and metal, electrons can be transferred from metal to PPy when the corrosion reaction occurs as follows: Oxidation reaction: Fe → Fe2+ + 2e (1) Reduction reaction: O2 + 2H2O + 4e- → 4OHPPy(A )(oxidation) + 2e → PPy(reduction) + A x- x- (2) (3) Figure 3.33 Bode diagrams of steel coated with PVB and PVB containing nanocomposites after 24 hours of immersion The oxidation reaction (1) provided electrons for the reduction reaction of PPy PPy at reduction form can release doped anions to form complex with ferric, which helps to prevent corrosion Oxalate 18 anions, with small size, is more mobility than dodecyl sulfate and benzoate, therefore, can be released easier to form complex Modulus impedance at low frequency |Z|100mHz is a very important parameter to evaluate the corrosion resistance of coating Figure 3.33 showed the |Z|100mHz values of different coatings after 24 hours of immersion in NaCl solution |Z|100mHz values were increased in the order: PVB < PVBSiO2/PPy < PVB-SiO2/PPyDoS < PVB-SiO2/PPyBz < PVB-SiO2/PPyOx These results confirmed the presence of doped anions can improve the corrosion resistance of PVB coaing The EIS results showed that PVB-SiO2/PPyOx are more resisitance to corrosion than PVB-SiO2/PPyDoS and PVBSiO2/PPyBz because of higher modulus impedance, especially at low frequency Therefore, EIS results are consistent with OCP results Figure 3.34 |Z|100mHz values of steel coated with PVB and PVB containing 10 wt% SiO2/PPy, SiO2/PPyOx, SiO2/PPyBz and SiO2/PPyDoS after 24 hours of immersion 3.3.1 Characterization of SiO2/PPyOx XRD diagrams of SiO2, PPy and SiO2/PPyOx nanocomposites with varying oxalate content was shown in figure 3.35 In comparison with pure SiO2, the characteristic peak of silica crystal showed a slight shift, from 2θ=260 to 2θ=230, which can be explained by the bonding of silica molecule to the polymer film The average crystal size was calculated, reaching approximately 22 nm Figure 3.35 XRD diagrams of (1) SiO2, (2) PPy, (3) SiO2/PPyOx1, (4) SiO2/PPyOx2 and (5) SiO2/PPyOx3 Figure 3.36 FT-IR spectra of SiO2/PPyOx1 (1), SiO2/PPyOx2(2) and SiO2/PPyOx3 (3) 19 Figure 3.36 showed the FT-IR spectra of SiO2/PPyOx nanocomposties synthesized with varying oxalate content Characteristic peak of SiO2/PPyOx had a slight shift in wavelength and a large change in peak intensity when compared with the spectrum of pure PPy and SiO2 This result indicated the association of PPy and SiO2 The characteristic peaks of PPy showed higher frequency shift, 1540 cm-1 to 1500 cm-1, 1458 cm-1 to 1450 cm-1, 1150 cm-1 to 1100 cm-1 Specially, FT-IR spectra showed the characteristic peak of oxalate anion at 1610 cm-1 Thus, FT-IR results confirmed the formation of SiO2/PPy nanocomposites and the association of oxalate anions in SiO2/PPyOx Figure 3.37 TGA diagrams of PPy (a), SiO2 (b), SiO2/PPy (c), SiO2/PPyOx1 (d), SiO2/PPyOx2 (e) and SiO2/PPyOx3 (f) The general characteristics in the decomposition of SiO2/PPyOx1, SiO2/PPyOx2 and SiO2/PPyOx3 are the TGA diagrams exhibited various transitions, demonstrating that samples had many components such as excess monomer, doped anions and products of incomplete olygomeric polymerization (figure 3.37) The decrease in mass (~9%) at low temperature (< 1000C) was explained by the evaporation of adsorbed water on the surface Then, the weight loss in the temperature in the range of 100-350oC was due to the decomposition of the oligomer and doped anions in the nanocomposites The decomposition temperature of PPy is in the range of 350-600oC Compared with TGA results of pure PPy, the decomposition temperature of PPy increased from 570 to 6600C, in the presence of silica and oxalate anions These results can be explained by the thermal stability of silica, which limits the thermal movements of the polypyrrole chain and protect the polymer framework from biodegradation The remaining weight at 800oC of SiO2/PPyOx1, SiO2/PPyOx2 and SiO2/PPyOx3 were 31, 38 and 42%, respectively 20 Figure 3.38 TEM photographs of (a) SiO2 (b) SiO2/PPy, (c) SiO2/PPyOx1, (d) SiO2/PPyOx2 and (e) SiO2/PPyOx3 It can be seen from TEM photographs (figure 3.38), synthesized silica was spherical with diameter of 40 nm In the case of nanocomposites SiO2/PPy, SiO2/PPyOx1, SiO2/PPyOx2 and SiO2/PPyOx3, the particles diameters were higher than that of silica and tend to be agglomerated This may due to te adsorption of pyrrole monomer on the silica surface with FeCl 3, which results in the increasing of particle size The difficulty here is the uniform dispersion of silica in the polypyrrole network due to the hydrophilic linkage of oxide When changing the oxalate concentration, the size of nanocomposites changed slightly (100-150nm) Table 3.9 EDX datas of SiO2/PPyOx1, SiO2/PPyOx2 and SiO2/PPyOx3 wt% Samples C O N Si Cl SiO2/PPyOx1 38,64 34,89 9,15 17,31 0,01 SiO2/PPyOx2 39,68 31,43 8,41 20,47 0,01 SiO2/PPyOx3 38,69 35,21 8,05 18,04 0,01 EDX datas of SiO2/PPyOx1, SiO2/PPyOx2 and SiO2/PPyOx3 were shown in table 3.9 With SiO2, oxygen and silicon are the two main elements In PPy, main elements are nitrogen and carbon The presence of the four elements indicated the linkage between PPy and SiO in nanocomposites The weight percentages of oxygen and carbon in nanocomposites tended to increase in SiO2/PPyOx1, SiO2/PPyOx2 and SiO2/PPyOx3, due to the increase of oxalate content in the initial reaction mixture 3.3.2 The effects of SiO2/PPyOx nanocomposites to epoxy coatings 3.3.2.1 Open circuit potential Figure 3.40 showed the variation of OCP over time of different samples OCP values tended to decrease sharply towards negative region, from -0.300 VSCE to -0,540 VSCE after 35 days of immersion with steel coated with epoxy It can be explained by phenomena on the steel surface such as the penetration of chloride ions into the coating The highest value of ESPO1, ESPO2 and ESPO3 was 0.200 VSCE; 0.310 VSCE and 0.250 VSCE, at the beginning This confirms that the coatings played an in important role to maintain the potential in passive zone, increasing the anticorrosion efficiency After 10 days of immersion, the OCP value of ESPO1, ESPO2 and ESPO3 decreased from 21 -0,150 VSCE; 0,150 VSCE and -0,090 VSCE, respectively The decrease of OCP can be explained by the diffusion of the electrolyte and corrosive ions that penetrate through the holes on the coating surface However, after this, OCP value increased and stabilized (0,020 VSCE; 0,190 VSCE and 0,011 VSCE with ESPO1, ESPO2 and ESPO3, respectively) after 21 days immersion This phenomenon is explained by the corrosion protection of SiO2/PPyOx nanocomposites in epoxy coatings in three following ways Firstly, nanocomposites reinforced the mechanical barrier protection for epoxy coatings In addition, when the steel camples contact with electrolyte solution, it caused PPy reduction and oxidation of steel to form oxide At the same time, PPy at polaron stage is converted into PPy at bipolaron stage, allowing the oxlate anions to be released at the interface between steel and coating, forming a passive complex Figure 3.40 The variation of OCP of samples over immersion time in 3% NaCl solution 3.3.2.2 Electrochemical Impedance Spectroscopy Figure 3.41 showed the Bode diagrams of coatings after hour of immersion On the correlation graph between phase angle and frequency, all samples represent only one phase component with a maximum phase angle of over 70 ° For ESPO1, ESPO2 and ESPO3 samples, the phase angle is high in the wide frequency range Observing the total impedance curve shows that, at the low frequency region, from 0.01 Hz to Hz, the characteristic of corrosion occurs on the boundary of the coating and the substrate (~ 107 Ω.cm-2) is much higher than EP (~ 106 Ω.cm-2) In the high frequency range, the total impedance of the ESP decreases and roughly corresponds to the EP pattern Epoxy-coated steel plates containing SiO2/ PPyOx nanocomposite are similar in form to SiO2/PPy However, the value is always higher, reaching 1.02×108; 5.02×109 and 2.69x108 Ω.cm-2 at low frequencies, 10 mHz At high frequencies, characteristic for the separation properties of the film, the linear impedance is linear, the capacitance and the resistance of the film are reduced in the order of ESPO2> ESPO3> ESPO1 Simultaneously from the diagram can see the ESPO2 model has the highest value of the module, the results confirmed that the ESPO2 coating has the best protection against corrosion 22 Figure 3.41 Bode diagrams of coatings after hour of immersion Figure 3.42 shows the Bode diagram of samples after days of immersion Total impedance values of the samples were slightly reduced in the low and medium frequency regions The phase diagram is maintained with a phase component, but with the EP and ESP models, the maximum phase angle decreases to approximately 60o Figure 3.42 Bode diagrams of coatings after days of immersion As can be seen in Figure 3.45, the protective epoxy resilience of the carbon steel substrate is reduced after 35 days of immersion At this point, the impedance of the EP sample is the same as that of the steel substrate In the low frequency region, the impedance of the ESP is still much higher than that of the EP However, in the medium and high frequency regions, this value is equivalent to, even lower than that of the epoxy This is explained as follows: For the ESP sample, the SiO2/PPy nanocomposite contained in the coating has significantly improved the protection of the steel substrate Silica nanoparticles act as a reinforcing material, enhancing the mechanical strength of the coating PPy, with its strong oxidation capacity, acts as a surface oxidizer for steel, which leads to the passage of steel into the passive region Over time, the ability of PPy to passivate steel is no longer at some points, leading to local corrosion This is confirmed by the phase diagram, which shows that the second phase component has not yet appeared, suggesting that the coating still has the ability to protect the local corrosion that results in a reduction in the total impedance 23 Figure 3.45 Bode diagrams of coatings after 35 days of immersion From the impedance spectra, the total modulus value at 100 mHz is determined to assess the corrosion resistance of the film The change in value |Z|100mHz of the samples is shown in Figure 3.46 For SPO1, SPO2 and SPO3 composite epoxy coatings, the value |Z|100mhz falls during the first 14 days of immersion This results in a decrease in the protective capacity of the subclass due to the diffusion of the invading ions Then, the |Z|100mhz values continue to decrease for pure epoxy coatings and epoxy containing SiO2/PPy For epoxy coating containing SiO2/PPyOx, |Z|100mhz increased and then decreased again after 21 days of immersion According to the published work, PPy is an intelligent conductive polymer that prevents corrosion of steel in two different ways; PPy acts as a physical barrier in the paint film, preventing the penetration of corrosive ions On the other hand, PPy is able to passively surface steel by forming iron oxides and iron complexes As an doped anion, oxalat anion liberation directly affects the corrosion resistance of the mantle, increasing the |Z|100mhz value After 35 days of immersion, the value of |Z|100mhz of the epoxy coating containing SPO2 is higher than that of other coatings This may be explained as follows: oxalate anion released from SiO2/PPyOx by exchange reaction with anions such as Cl- and OH- Oxalate anions free can form complexes with iron, forming passive complexes, which increases the resistance to corrosion Figure 3.46 The variation of |Z|100mHz over immersion time From the corrosive behavior of the samples after immersion in NaCl solution, we can confirm the effect of the addition of anion oxalate to the SiO2/PPy nanocomposites in increasing corrosion resistance of the epoxy coating for carbon steel 24 3.3.2.3 Salt spray test Photographs of steel coated with epoxy and epoxy containing SiO2/PPy and SiO2/PPyOx after 28 days of salt spray test are shown in Figure 3.47 With EP samples, multiple rusts and blistering along the incision were noted In addition, many blisters appear on the mantle surface This results in a decrease in the adhesion of the coating to the steel surface of the test chamber This phenomenon can be explained by the invasion of ionized ions into the metal surface For ESP specimens, blisters and blisters appear less For steel samples coated with epoxy containing SiO2/PPyOx nanocomposite, especially ESPO2 samples, no rust or blistering, and very little corrosion products along the incision Salt spray test results confirmed the best corrosion protection by epoxy coating containing ESPO2, in accordance with the results of other experiments Figure 3.47 Photographs of steel coated with epoxy and epoxy containing SiO2/PPy and SiO2/PPyOx after 28 days 3.3.2.3 Corrosion protection mechanism of epoxy coating containing SiO2/PpyOx nanocomposites From the results obtained, the corrosion protection mechanism of the epoxy coating containing the SiO2/PPyOx nanocomposite was proposed as follows (Figure 3.48): - Epoxy coating acts as a barrier, preventing the entry of corrosive agents into the steel surface Simultaneously, the nanocomposite SiO2/PPy exhibited a double protective role SiO2 acts as a reinforcement, enhances the barrirer protection of the epoxy coating PPy has the anode protection ability, play the role of passive steel substrate, shift the voltage of the steel towards the positive - As the protective ability of the coating decreases, the corrosive agent starts attacking the steel surface, the steel is oxidized, releasing electrons [140]: Fe → Fe2++2e Fe2+ → Fe3++e Formation of iron hydroxide and oxide leads to reactions: 2OH- + Fe2+ → Fe(OH)2 2Fe(OH)2 + O2 → 2Fe(OH)3 2Fe(OH)3 → Fe2O3+ 3H2O Free eletrons involved in the reaction with oxygen: O2 + 4e + 2H2O → 4OH- When corrosion occurs, PPy is reduced, the oxalate anion in PPy has the ability to inhibit corrosion that is released and prevented corrosion of the metal at corroded sites by the formation of iron complexes [141] PPyn+ C2O42- + me PPy(n-m)+ C2O42- + C2O42- 25 2Fe3++ 3C2O42- → Fe2(C2O4)3 Figure 3.48 Corrosion protection mechanism of epoxy containing SiO2/PPyOx nanocomposites CONCLUSION Successfully synthesized silica/polypyrrole nanocomposite in aqueous solution in presence of 2.5 mmol silica; mmol pyrol; 0.05 mol FeCl3.6H2O by in-situ method, Nanocomposite obtained in spherical form, diameter is about 50-100 nm The corrosive behavior of carbon steel in a 3% NaCl solution containing silica/polypyrrole nanocomposite was studied by open circuit potential method The results show that nanocomposite silica/polypyrrole is capable to shift the potential of steel to passivate region, which shows the inhibitive ability Doped silica/polypyrrole nanocomposite with different anions such as: dodecyl sulfate, benzoate or oxalate was successfully synthesized by in-situ method The results of IR, EDX, XRD, and TGA analysis confirmed the anion linkage with nanocomposite The SEM, TEM photographs show that the synthesized nanocomposite are spherical in shape, varying in diameter from 50-150 nm Corrosion behavior of carbon steel coated with PVB containing 10 wt% silica/polypyrrole and silica/polypyrrole-doped was studied to investigate the inhibitive effect of the nanocomposite with organic coating The results showed that the presence of nanocomposite SiO2/PPy-Ox, SiO2/PPy-Dos and SiO2/PPy-Bz significantly increase the corrosion resistance of PVB coatings Epoxy coatings containing nanocomposite SiO2/PPy or SiO2/ PPy-Ox with different oxalates content were prepared and compared with non-nanocomposite epoxy coatings The results showed that composite SiO2/PPy-Ox significantly increased protection performance of epoxy coating, the highest protection effect was obtained with ESPO2 with pyrrole/oxalate ratio of 0.4 26 LIST OF WORKS HAS BEEN PUBLISHED Vu Thi Hai Van, To Thi Xuan Hang, Pham Thi Nam, Nguyen Thi Thom, Nguyen Thu Phuong, Devilliers Didier, Dinh Thi Mai Thanh - Synthesis of silica/polypyrrole nanocomposites and application in corrosion protection of carbon steel, Journal of Nanoscience and Nanotechnology 18 (2018) 4189-4195 Vu Thi Hai Van, Dinh Thi Mai Thanh, Pham Thi Nam, Nguyen Thi Thom, Nguyen Thu Phuong, To Thi Xuan Hang – Evaluation of the Corrosion Inhibiting Capacity of Silica/Polypyrrole-Oxalate nanocomposite in Epoxy Coatings, International Journal of Corrosion 2018 (2018), Article ID 6395803 Vũ Thị Hải Vân, Phạm Thị Năm, Nguyễn Thị Thơm, Nguyễn Thu Phương, Tô Thị Xuân Hằng, Đinh Thị Mai Thanh - Synthesis, characterization and corrosion inhibitor ability of composites silica-polypyrrole, Vietnam Journal of Chemistry, Vol 55 (6), 2017, pp 781-786 Vũ Thị Hải Vân, Nguyễn Thị Nga, Phạm Thị Năm, Nguyễn Thị Thu Trang, Tô Thị Xuân Hằng, Đinh Thị Mai Thanh, Tổng hợp đặc trưng nanocompozit silica/polypyrol (SiO2/PPy), Tạp chí Hóa học, ISSN: 0866-7144, tập 54, trang 149154 (2016) Vu Thi Hai Van, Pham Thi Nam, Nguyen Thi Thom, Nguyen Thu Phuong, Nguyen Thi Thu Trang, To Thi Xuan Hang, Dinh Thi Mai Thanh – The role of counter anions in anticorrosive properties of silica-polypyrrole composite Vietnam Journal of Science and Technology, 563 B, 2018, 104-116 Vũ Thị Hải Vân, Nguyễn Thị Nga, Phạm Thị Năm, Tô Thị Xuân Hằng, Đinh Thị Mai Thanh – Synthesis, characterization and inhibitive ability of nanocomposites silica-polypyrrole, The 5th Asian Materials Data Symposium, 2016 Vũ Thị Hải Vân, Phạm Thị Năm, Tô Thị Xuân Hằng, Đinh Thị Mai Thanh – Effect of counter anions in nanocomposites silica/polypyrrole on corrosion protection of polyvinylbutyral coating, The 8th International Workshop on Advanced Materials Science and Nanotechnology, 2016 27 ... application in organic coatings for anticorrosion Therefore, the thesis "Synthesis and characterization of silica/polypyrrole nanocomposite oriented for use in organic corrosion protection coatings"... contributing to the synthesis and application of silica/polypyrrole nanocomposite in the field of corrosion protection The main contents and objectives of the thesis - Investigation of the synthesis. .. decrease for pure epoxy coatings and epoxy containing SiO2/PPy For epoxy coating containing SiO2/PPyOx, |Z|100mhz increased and then decreased again after 21 days of immersion According to the