The main contents and objectives of the thesis: Synthesis of hydrotalcite bearing benzothiazolylthiosuccinic acid (BTS) modified by silane and applied in solventborne epoxy coating for corrosion protection of carbon steel.
VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY NGUYEN TUAN ANH Project name: SYNTHESIS OF HYDROTALCITES BEARING CORROSION INHIBITORS AND FABRICATION OF NANOCPMPOSITE COATINGS FOR CORROSION PROTECTION OF CARBON STEEL Major: Organic chemistry Code: 9.44.01.14 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, Institute for Tropical Technology Vietnam Academy of Science and Technology Assoc Prof Dr Trinh Anh Truc, Institute for Tropical Technology Vietnam Academy of Science and Technology A INTRODUCTION The urgency of thesis Corrosion of metal causes great damage to the economy of countries in the world as well as in Vietnam, so the corrosion protection of metals is very necessary Organic coatings are widely used for corrosion protection of metal structures Pigment inhibits corrosion in paint film plays an important role in ensuring the anti-corrosion protection of coatings Chromates are the best inhibitive pigments, but due to their high toxicity and unfriendly to the environment, it is increasingly limited in their use There have been many research to study the replacement of chromates in organic coatings by nontoxic pigments and additives One of atractive researchs is the fabrication of inhibitive pigments based on hydrotalcite The application of hydrotalcites is based on their ability to absorb and exchange anion, and flexibility of anions between the layers The coatings containing hydrotalcites bearing organic anions such as benzotriazolate and oxalate have also been studied In addition, hydrotalcites containing decavanadate, vanadate have been studied and applied in the anti-corrosion protection coating for aluminum and magnesium alloys However, these coatings are not as protective as the coatings containing chromates The protective properties of organic coatings containing hydrotalcites depend on the dispersion of hydrotalcite in the polymer matrix To improve the dispersion of hydrotalcite in the polymer matrix, silane compounds are used to modify the hydrotalcite surface In addition, the presence of silane improves the adhesion between film containing hydrotalcite bearing corrosion inhibitor and metal surfaces Therefore, the title of thesis is “Synthesis of hydrotalcites bearing corrosion inhibitors and fabrication of nanocomposite coatings for corrosion protection of carbon steel” This work contributes to the development of metal anti-corrosion protection coatings The main contents and objectives of the thesis - Synthesis of hydrotalcite bearing benzothiazolylthiosuccinic acid (BTS) modified by silane and applied in solventborne epoxy coating for corrosion protection of carbon steel: + Synthesis and structural analysis of hydrotalcite bearing benzothiazolylthiosuccinic acid modified by silane + Study on corrosion inhibiting ability for steel of hydrotalcite bearing benzothiazolylthiosuccinic acid modified by silane + Influence of hydrotalcite bearing benzothiazolylthiosuccinic acid modified by silane on corrosion protection performance of solventborne epoxy coating - Synthesis of hydrotalcite bearing molydate modified by silane and applied in waterborne epoxy coating for corrosion protection of carbon steel: + Synthesis and structural analysis of hydrotalcite bearing molydate modified by silane + Study on corrosion inhibiting ability for steel of hydrotalcite bearing molydate modified by silane + Influence of hydrotalcite bearing molydate modified by silane on corrosion protection performance of waterborne epoxy coating Scientific significance, practice and new contributions of the thesis - Successful synthesis of hydrotalcites containing corrosion inhibitors (benzothiazolylthiosuccinic acid and molybdate) and application of modified hydrotalcites in organic coatings for corrosion protection of carbon steel Hydrotacite containing benzothiazolylthiosuccinic acid with surface modified by silane has corrosion inhibition efficiency of 96% at g/L concentration Hydrotakcite containing molydate with surface modified by silane has has corrosion inhibition efficiency of 95% at g/L The result is also a premise to open up a research direction is application of hydrotalcite bearing corrosion inhibitor with silane modified surface in corrosion protection of carbon steel - Preparation of the epoxy coating containing hydrotalcite intercalated with corrosion inhibitors for corrosion protection of carbon steel The modification by silane has improved the dispersion of hydrotalictes in epoxy, thus enhancing the inhibition effect of hydrotalcite in epoxy coatings Structure of the thesis The thesis includes 127 pages Introduction: pages; Chapter Background Overview: 36 pages; Chapter Experiment: 16 pages; Chapter Results and discussions: 59 pages; Conclusion: pages; New contributions of the thesis: page; List of author’s reports published: page; 25 tables, 73 figures and 87 references B CONTENT OF THE THESIS Chapter 1: OVERVIEW The thesis gives the bibliography of organic coatings, corrosion inhibitors, organic modified hydrotalcite and application of hydrotalcite in organic coatings Chapter 2: EXPERIMENTAL AND RESEARCH METHODS 2.1 Chemicals, materials and instruments 2.1.1 Chemicals and materials a) Chemicals: Al(NO3)3.9H2O, Zn(NO3)2.6H2O, Na2MoO4 2H2O (sodium molybdate inhibitor), C11H9O4S2N (benzothiazolylthiosuccinic acid inhibitor, C8H22O3N2Si (N-(2-aminoethyl)-3-aminopropyltrimethoxisilan) , C9H20O5Si (3-glycidoxipropyltrimethoxi silan), NaCl, C2H5OH, C8H10 (xylen), NaOH, YD-011X75 epoxy (Kudo), EPON 828 epoxy (Hexion), Polyamin 307D-60 hardener (Kudo), EPIKURE 8537-WY-60 hardener (Hexion) b) Materials - Hydrotalcite, hydrotalcite bearing corrosion inhibitor and hydrotalcite bearing corrosion inhibitor modified by silane powder - Carbon steel composition: Fe = 98%; C = 0.14 – 0.22%; Si = 0.05 – 0.17%; Mn = 0.4 – 0.65%; Ni ≤ 0.3%; S ≤ 0.05%; P ≤ 0.04%; Cr ≤ 0.3%; Cu ≤ 0.3%; and As ≤ 0.08% The working surface area is cm2 soaked in 0.1 M NaCl solution, 0.1 M NaCl solution containing modified hydrotalcite - The carbon steel sheets with a size of 10 × 15 × 0.2 cm are coated a solventborne epoxy coating containing modified hydrotalcite and a waterborne epoxy coating containing modified hydrotalcite 2.1.2 Instruments Glass cups of 200 mL, 500 mL, and 1000 mL; Globe bottle with flat bottom and neck of 250 mL and 500 mL; Hopper drip; convection tube; glass chopstick; Stove with magnetic stirrer; Vacuum cabinet; pH meter; SiC papers, from P400 to P1200 grit (Japan); spin-coater machine 2.2 Synthesis of hydrotalcite, hydrotalcite bearing corrosion inhibitor and hydrotalcite bearing corrosion inhibitor modified by silane 2.2.1 Synthesis of hydrotalcite Hydrotalcite is synthesized in globe bottle with flat bottom and neck (500 mL) as follows: 90 mL solution containing 0.03 M Zn(NO3)2, and 0.015 M Al(NO3)3 is added drop into 145 mL solution of 0.0313 M NaOH during hour The reaction was conducted in N2 gas, stirred and refluxed at 65 °C pH solution is adjusted at 8-10 by using the concentrated M NaOH solution After 24 hours of reaction, the precipitate obtained is filtered and washed several times with distilled water (water removed CO2) The precipitate was dried 24 hours at 50 0C under vacuum and obtained g hydrotalcite The experiment was repeated three times 2.2.2 Synthesis of hydrotalcite bearing benzothiazolylthiosuccinic acid Hydrotalcite bearing benzothiazolylthiosuccinic acid (HTBA) is synthesized in globe bottle with flat bottom and neck (500 mL) as follows: 90 mL solution containing 0.03 M Zn(NO3)2, and 0.015 M Al(NO3)3 is added drop into 145 mL solution containing 0.06 M benzothiazolylthiosuccinic acid and 0.0313 M NaOH during hour The reaction was conducted in N2 gas, stirred and refluxed at 65 °C pH solution is adjusted at 8-10 by using the concentrated M NaOH solution After 24 hours of reaction, the precipitate obtained is filtered and washed several times with ethanol/ distilled water The precipitate was dried 24 hours at 50 0C under vacuum and obtained 7.5 g hydrotalcite bearing benzothiazolylthiosuccinic acid The experiment was repeated three times 2.2.3 Synthesis of hydrotalcite bearing benzothiazolylthiosuccinic acid modified by N - (2-aminoethyl) -3-aminopropyltrimethoxisilane Hydrotalcite bearing benzothiazolylthiosuccinic acid modified by N (2-aminoethyl) -3-aminopropyltrimethoxisilane (HTBAS) is synthesized in globe bottle with flat bottom and neck (250 mL) as follows: Hydrotalcite bearing benzothiazolylthiosuccinic acid (HTBA) is dispersed in ethanol The ethanol solution containing HTBA is added drop into 20 mL solution containing N - (2-aminoethyl) -3-aminopropyltrimethoxisilane during 30 (Silane content is 3% compared to HTBA) The reaction mixture is stirred at 60 °C for hours, then filtered and washed with ethanol The precipitate was dried 24 hours at 50 0C under vacuum and obtained HTBAS with content of 3% silane compared to HTBA The experiment was repeated three times 2.2.4 Synthesis of hydrotalcite bearing molydate Hydrotalcite bearing molydate is synthesized in globe bottle with flat bottom and neck (500 mL) as follows: 90 mL solution containing 0.03 M Zn(NO3)2, and 0.015 M Al(NO3)3 is added drop into 145 mL solution containing 0.0313 M molydate and 0.0313 M NaOH during hour The reaction was conducted in N2 gas, stirred and refluxed at 65 °C pH solution is adjusted at 8-10 by using the concentrated M NaOH solution After 24 hours of reaction, the precipitate obtained is filtered and washed several times with distilled water (water removed CO2) The precipitate was dried 24 hours at 50 0C under vacuum and obtained 6.5 g hydrotalcite bearing molydate The experiment was repeated three times 2.2.5 Synthesis of hydrotalcite bearing molydate modified by N - (2aminoethyl) -3-aminopropyltrimethoxisilane Hydrotalcite bearing molydate modified by N - (2-aminoethyl) -3aminopropyltrimethoxisilane (HTMS) is synthesized in globe bottle with flat bottom and neck (250 mL) as follows: Hydrotalcite bearing molydate (HTM) is dispersed in ethanol The ethanol solution containing HTM is added drop into 20 mL solution containing N - (2-aminoethyl) -3aminopropyltrimethoxisilane during 30 (Silane content is 3% compared to HTM) The reaction mixture is stirred at 60 °C for hours, then filtered and washed with ethanol The precipitate was dried 24 hours at 50 0C under vacuum and obtained HTMS with content of 3% silane compared to HTM The experiment was repeated three times 2.2.6 Synthesis of hydrotalcite bearing molydate modified by 3glycidoxipropyltrimethoxisilane Hydrotalcite bearing molydate modified by 3glycidoxipropyltrimethoxisilane (HTMGS) is synthesized in globe bottle with flat bottom and neck (250 mL) as follows: Hydrotalcite bearing molydate (HTM) is dispersed in ethanol The ethanol solution containing HTM is added drop into 20 mL solution containing 3glycidoxipropyltrimethoxisilane during 30 (Silane content is 3% compared to HTM) The reaction mixture is stirred at 60 °C for hours, then filtered and washed with ethanol The precipitate was dried 24 hours at 50 0C under vacuum and obtained HTMGS with content of 3% silane compared to HTM The experiment was repeated three times 2.3 Preparation of epoxy coating containing modified hydrotalcite 2.3.1 Preparation of steel samples The carbon steel with size 10×15×0.2 cm was cleaned of surface rust, washed with distilled water, ethanol and then dried 2.3.2 Preparation of solventborne epoxy coating containing modified hydrotalcite The epoxy coatings containing HTBA 3% (EP-HTBA), HTBAS 3% (EP-HTBA), HTM 3% (EW-HTM), HTMS 3% (EW-HTMS), and HTMGS 3% (EW-HTMGS) are prepared by a spin-coater machine After drying, the thickness of the coating is 30 μm 2.4 The analytical methods IR and UV-vis spectra were measured at Institute for Tropical Technology XRD diagrams and FESEM images were realized at Institute of Material Science AAS analysis were realized at Institute of Chemistry 2.5 Electrochemical methods Polarization curves and electrochemical impedance spectra were carried out on AUTOLAB equipment at Institute for Tropical Technology 2.6 Mechanical properties Adhesion (ASTM D4541-2010) and impact resistance (ISO D58675) of coatings were measured at the Institute for Tropical Technology 2.7 Salt spray test The samples were tested in salt spray chamber according to ASTM B117 standard at Institute for Tropical Technology Chapter RESULTS AND DISCUSSTION 3.1 Synthesis of hydrotalcite bearing benzothiazolylthiosuccinic acid (BTS) modified by silane and applied in solventborne epoxy coating for anti-corrosion protection of carbon steel 3.1.1 Synthesis and structural analysis of hydrotalcite bearing benzothiazolylthiosuccinic acid modified by N - (2-aminoethyl) -3aminopropyltrimethoxisilane Table 3.1: The physical state of the samples No Samples The physical state HT Precipitation with fine powder, white HTBA Precipitation with fine powder, light yellow HTBAS Precipitation with fine powder, light yellow 3.1.1.1 Structural analysis by IR spectra * IR spectra of BTSA, HT, HTBA The IR spectra and the characteristic bands of BTSA, HT, HTBA are shown in Figure 3.1 and Table 3.2 Fig 3.1: IR spectra of BTSA (a), HT (b) and HTBA (c) Table 3.2: IR spectra analysis of BTSA, HT, HTBA Wavenumber (cm-1) Shape Intensity Vibration BTSA HT HTBA 420 - 670 423 - 630 Narrow Weak δZn-O, δAl-O, δAl-O-Zn 995 990 Narrow Weak δC-H (Aromatic) Narrow Strong 1367 1363 NO2 (-O-NO2) 1634 1595 Narrow Strong δOH (H2O) Narrow Strong 1721 C=O (-COOH) Narrow Strong 1423 C=C (Aromatic) Narrow 1520 Weak C=O (-COO-) 3421 3434 3445 Broad Strong O-H IR results showed that BTSA was inserted into the structure of hydrotalcite In the structure of HTBA, BTSA is in the carboxylate form + IR spectra of N - (2-aminoethyl) -3-aminopropyltrimethoxisilane (APS), HTBA and HTBAS The IR spectra and the characteristic bands of of APS, HTBA, and HTBAS samples are shown in Figure 3.2 and Table 3.3 Fig 3.2: IR spectra of APS (a), HTBA (b) and HTBAS (c) Table 3.3: IR spectra analysis of APS, HTBA, HTBAS Wavenumber (cm-1) Shape Intensity Vibration APS HTBA HTBAS Narrow δZn-O, δAl-O, Weak 420 - 670 423 - 630 δAl-O-Zn 990 990 Narrow Weak δCH (Aromatic) Narrow Strong 1363 1363 NO2 (-O-NO2) Narrow Weak 1520 1520 C=O (-COO-) 1595 1595 Narrow Strong δOH (H2O) 1640 1650 Narrow Medium δNH(-NH2) CH2, CH3 2940, 2840 Narrow Medium Strong 3410 3445 3440 Broad O-H, N-H Results of the spectrum analysis of APS, HTBA and HTBAS showed that APS was inserted into the structure of HTBAS 3.1.1.2 Structural analysis by XRD pattern Fig 3.3: XRD pattern of HT (a), HTBA (b) and HTBAS (c) XRD analysis (Fig 3.3) showed that the distance between layers of HTBA or HTBAS are higher than that of HT, which suggests that the BTSA is inserted into hydrotalcite and increases the layer distance of hydrotalcite 3.1.1.3 Mophology analysis by SEM Fig 3.4: SEM images of HTBA Fig 3.5: SEM images of HTBAS SEM images show that HTBA (Fig 3.4) and HTBAS (Fig 3.5) have plates shape with size about 50-200 nm HTBAs are relatively clustered, while HTBASs are separated and have smaller particle sizes The size reduction and separation may be explained by the silane reaction with the OH- group on the HT surface which reduces the bonding of HT particles 3.1.1.4 Content of benzothiazolylthiosuccinic acid in HTBA and HTBAS HTBA HTBAS Fig 3.6: UV-VIS spectra of 100 times diluted solution of HTBA after reaction with HNO3 Fig 3.7: UV-VIS spectra of 100 times diluted solution of HTBAS after reaction with HNO3 Table 3.4: Absorption intensity of solutions No Samples Absorption intensity HTBA 0.141 HTBAS 0.151 Table 3.5: BTSA concentration and content of solutions Concentration No Samples Sample mass Content BTSA (%) BTSA (M) HTBA 0.00151 0.0309 34.6 HTBAS 0.00147 0.0309 33.69 Analysis results show that the content of BTSA in HTBA and HTBAS are not much different Thus, surface modification by silane does not affect the content of BTSA present in HTBAS 3.1.1.5 Analysis of silanization reaction of hydrotalcite bearing benzothiazolylthiosuccinic acid corrosion inhibitor On the surface of hydrotalcite, the major component is hydroxyl groups (-OH) According to the mechanism of silanization reaction, the 3.1.3.3 Mechanical properties of epoxy coatings with HTBA and HTBAS Table 3.9: Adhesion and impact resistance of epoxy coatings with HTBA and HTBAS Samples Adhesion (N/mm2) Impact resistance (kg.cm) EP0 1.5 180 EP-HTBA 2.0 180 EP-HTBAS 2.2 180 The results showed that HTBA with silnae modified surface increased adhesion of epoxy coatings 3.1.3.4 Salt spray test (a) (b) Fig 3.21: Photographs of steel coated EP0 (a), EPHTBA (b) and EP-HTBAS after 96 h salt spray test with 3% NaCl solution (c) The results of the salt spray test (Fig 3.21) of the samples showed that modification with silane increased the protection of the epoxy coatings This result is in agreement with the results of impedance measurement and adhesion 3.1.3.5 Corrosion protection mechanism of solventborne epoxy coatings with HTBA and HTBAS Hydrotalcite bearing BTSA with surface modified by silane (APS), thus enhanced the dispersion of hydrotalcite bearing corrosion inhibitor in epoxy coating This may be explained that the silane activates at the interface between the inorganic compound (hydrotalcite) and the organic compound (solventborne epoxy coating) to bond or pair up these two incompatible materials (the result of HTBAS dispersion in epoxy coatings was demonstrated by SEM images, X-ray diffraction and IR spectra in section 3.1.3.1.) The bond between the modified hydrotalcite and the solventborne epoxy coatings is simulated in Figure 3.22 Fig 3.22: Simulate the interconnection between modified hydrotalcite and epoxy coatings 15 On the other hand, the presence of HTBAS will significantly increase the adhesion of the epoxy coatings ( the result in section 3.1.3.3) This can be explained that the modified hydrotalcite has the ability to adsorb onto the surface of the metal, thus increasing the bonding capacity between the epoxy and the metal surface Thus, the presence of HTBA and HTBAS in the solventborne epoxy coatings increases barrier properties and corrosion resistance of the coatings Especially when the paint film is defected, under the effect of aggressive environment (Cl- anion), hydrotalcite bearing BTSA corrosion inhibitor in the paint film will occur ion exchange reactions As a result, the BTSA will be released from hydrotalcite to protect the carbon steel and Cl- ions will be retained in the hydrotalcite structure The corrosion protection mechanism of the epoxy coatings containing hydrotalcite bearing BTSA corrosion inhibitor is shown in Figure 3.23 Fig 3.23: The corrosion protection mechanism of the epoxy coatings containing hydrotalcite bearing BTSA corrosion inhibitor Summary of Section 3.1 The hydrotalcite intercalated with benzothiazolylthiosuccinic acid corrosion inhibitor (HTBA) was successfully synthesized and its surface was modified by N-(2-aminoethyl)-3-aminopropyltrimethoxisilane (HTBAS) The HTBA and HTBAS have a particle size of 50-200 nm Electrochemical measurements show that HTBA and HTBAS are anodic corrosion inhibitors, and inhibition efficiency achieve 96% at a concentration of g/L in ethanol/water (2/8) solution contain 0.1 M NaCl Their presence has significantly increased the protective performance of the solventborne epoxy coatings The surface modification with silane has the effect of increasing dispersibility, thus enhancing the reinforcing effect of hydrotalcite bearing BTSA inhibitor in epoxy coatings 3.2 Synthesis of hydrotalcite bearing molypdate modified by silane and applied in watertborne epoxy coatings for corrosion protection of carbon steel 3.2.1 Synthesis and structural analysis of hydrotalcite bearing molypdate modified by N - (2-aminoethyl) -3-aminopropyltrimethoxisilane and - glycidoxipropyltrimethoxisilane 16 Table 3.10: The physical state of the samples No Samples The physical state HTM Precipitation with fine powder, white HTMS Precipitation with fine powder, white HTMGS Precipitation with fine powder, white 3.2.1.1 Structural analysis by IR spectra * IR spectra of natrimolypdate, HT, and HTM The IR spectra of Natrimolypdate, HT and HTM samples are shown in Figure 3.24 and Table 3.11 Fig 3.24: IR spectra of natri molypdate (a), HT (b), and HTM(c) Table 3.11: IR spectra analysis of natrimolypdate, HT, HTM Wavenumber (cm-1) Shape Intensity Vibration Natrimolypdate HT HTM δZn-O, δAl420 - 670 423 - 630 Narrow Weak O, δAl-O-Zn Mo-O840 835 Narrow Medium Mo (MoO42-) Narrow Strong NO2 (-O1367 1367 NO2) 1640 1634 1635 Narrow Strong δOH (H2O) 3441 3425 Broad Strong 3445 O-H Results of the spectrum analysis of molypdate, HT, and HTM showed that MoO42- was inserted into the structure of HTM This result is consistent with previous publications * IR spectra of APS, HTM, GS, HTMGS Fig 3.25: IR spectra of APS (a), HTMS (b), GS (c) and HTMGS (d) 17 Table 3.12: IR spectra analysis of APS, HTMS, GS, HTMGS Wavenumber (cm-1) Shape Intensity Vibration APS HTMS GS HTMGS 428, 618 437, 620 Narrow Weak δZn-O, δAl-O Mo-O-Mo 835 830 Narrow Medium (MoO42-) 1083 1090 1385 1640 1094 1365 Narrow Medium Narrow Strong Narrow Medium Medium Narrow Si-O-Si NO2(-O-NO2) δNH(-NH2) 1635 2940, 2944, 2942, CH2, CH3 2840 2843 2844 Strong 3370 3428 3513 3428 Broad O-H,N-H Results of the spectrum analysis of GS and HTMGS showed that GS has appeared on the surface of HTMGS 3.2.1.2 Structural analysis by XRD pattern Fig 3.26: XRD pattern of HTM (a), HTMGS (b) and HTMS (c) Results of the XRD pattern analysis (Fig 3.26) showed that MoO42was inserted into the structure of HTM and increased the layer distance of hydrotalcite APS and GS mainly adhered to the hydrotalcite surface without inserting between the hydroxide layers 3.2.1.3 Mophology analysis by SEM Fig 3.27: SEM images of HTM (a), HTMGS (b) and HTMS (c) SEM images (Fig 3.27) showed that HTM had plates shape with size about 50-200 nm, thickness of about 2-4 nm HTMS and HTMGS had plates shape and similer Compared to HTM, the HTMS and HTMGS had a smaller thickness and more separation 18 3.2.1.4 Content of molypdate in HTM, HTMS and HTMGS Table 3.13: Results of molypdate content analysis in HTM and HTM modified silane Samples Mo content (%) MoO42- content (%) HTM 8.99 15.0 HTMS 7.91 13.2 HTMGS 7.49 12.5 Analysis results showed that the content of molypdate in HTM, HTMS and HTMGS was 15.0 %, 13.2 % and 12.5%, respectively The results of this analysis had confirmed the insertion of molypdate into the HT structure 3.2.1.5 Analysis of silanization reaction of hydrotalcite bearing moypdate corrosion inhibitor On the surface of hydrotalcite, the major component is hydroxyl groups (-OH) The silanization reaction mechanism of hydrotalcite by N(2-aminoethyl)-3-aminopropyltrimethoxisilane and 3glycidoxipropyltrimethoxisilane is presented as Section 3.1.1.5 The silanization reaction of hydrotalcite bearing molypdate inhibitor is shown in Figure 3.28 and 3.29 The hydrotalcite surface is silanized with APS Hydroxide layer Corrosion inhibitor Hydroxide layer Fig 3.28: Silanization reaction of hydrotalcite by N-(2-aminoethyl)-3aminopropyltrimethoxisilane 19 The hydrotalcite surface is silanized with GS Hydroxide layer Corrosion inhibitor Hydroxide layer Fig 3.29: Silanization reaction of hydrotalcite by 3-glycidoxipropyltrimethoxisilane 3.2.2 Study on corrosion inhibition for carbon steel of HTM, HTMS and HTMGS 10 10 I / A.cm-2 10 10 10 10 10 10 -1 Fig 3.30: The polarization curves of steel after 2h immersion in 0.1 M NaCl solution without corrosion inhibitor (-), with g/L HTM (◊), with g/l HTMS (o) and with g/L HTMGS (×) -2 -3 -4 -5 -6 -7 -8 -0,8 -0,6 -0,4 E / VSCE -0,2 The results of the polarization curves analysis (Fig 3.30) showed that HTM, HTMS and HTMGS were anodic inhibitors The HTM surface modification by APS and GS slightly increased the corrosion inhibiting ability of HTM 20 Fig 3.31: The Nyquist plot of steel after 2h immersion in 0.1 M NaCl solution without corrosion inhibitor (a), with g/L HTM (b), with g/l HTMS (c) and with g/L HTMGS (d) Table 3.14: RP value and corrosion inhibitory yield of solutions with HTM, HTMS and HTMGS Solutio Rp Inhibition (Ω.cm2) efficiency (%) 170 0.1 M NaCl solution without corrosion inhibitor 2370 92.8 0.1 M NaCl solution with 3g/L HTM 3810 95.5 0.1 M NaCl solution with 3g/L HTMS 3590 95.3 0.1 M NaCl solution with 3g/L HTMGS The results in Table 3.14 showed that the inhibition efficiency of HTM was quite high, reaching 92.8% at g/L concentration The inhibition efficiencies of HTMS and HTMGS were higher than that of HTM and reaching 95.5% and 95.3%, respectively The inhibition efficiencies of HTM modified by two types of silane were not much different The increase in the inhibition efficiency of HTM modified with silane could be explained by the interaction of silane on the hydrotalcite surface with steel surfaces (a) (b) (a) mm (c) (b) mm (d) (c) (d) Fig 3.32: Photographs of steel Fig 3.33: SEM images of steel after 2h after 2h immersion in 0.1 M immersion in 0.1 M NaCl solution without NaCl solution without corrosion inhibitor (a), with g/L HTM corrosion inhibitor (a), with (b), HTMS (c) and HTMGS (d) g/L HTM (b), HTMS (c) and HTMGS (d) 21 2930, 2850 2930, 2850 1250 1050 22 425 3450 2930, 2850 1250 3450 1050 425 3450 1250 425 2920, 2850 1250 3450 1050 * EDX Tale 3.15: EDX result of steel surface after 2h immersion in 0.1 M NaCl solution without corrosion inhibitor, with g/L HTM, HTMS and HTMGS Solution O (%) Fe (%) Zn (%) Al (%) Mo (%) Si (%) 0.1 M NaCl 18.41 81.86 0.1 M NaCl 5.93 87.74 4.06 0.89 1.38 + g/L HTM 0.1 M NaCl 6.13 82.6 5.63 1.37 2.66 1.60 + g/L HTMS 0.1 M NaCl 7.45 79.26 8.86 1.12 2.13 1.17 + g/L HTMGS The EDX analysis results had confirmed the corrosion inhibition ability of HTM, HTMS and HTMGS due to the release of molybdate from HT and hydrotalcite adsorption on the steel surface The HTM surface modification with silane improved hydrotalcite adsorption on the steel surface, thus increasing corrosion inhibition effect 3.2.3 The effects of HTM and HTM modified silane on corrosion protection of waterborne epoxy coatings Table 3.16: Composition of waterborne epoxy coatings Modified hydrotalcite content in No Sample waterborne epoxy coatings (%) EW0 EW-HTM 3 EW-HTMS EW-HEMGS 3.2.3.1 Structure of waterborne epoxy coatings containing HTM, HTMS, HTMGS * IR spectra The IR spectra of waterborne epoxy coatings containing HTM, HTMS and HTMGS are shown in Figure 3.34 and Table 3.17 Fig 3.34: IR spectra of EW0 (a), EW-HTM (b), EW-HTMS (c), EWHTMGS (d) Table 3.17: IR spectra analysis of EW0, EW-HTM, EW-HTMS, EW-HTMGS Wavenumber (cm-1) Shape Intensity Vibration EWEWEWEW0 HTM HTMS HTMGS δZn-O, δAl-O, Weak 425 425 425 Narrow δAl-O-Zn 1050, 1050, 1050, 1050, C-O-C Weak Narrow (epoxy) 1250 1250 1250 1250 δNH, δOH 1660 1660 1660 1660 Narrow Medium (H2O) 2850, 2850, 2850, 2850, Narrow Medium CH3, CH2 2920 2930 2930 2930 3450 3450 3450 3450 Broad Strong N-HO-H The IR spectra analysis of waterborne epoxy coatings containing HTM, HTMS, and HTMGS showed that the coatings with the presence of hydrotalcite still exhibited characteristic peaks of epoxy So structure epoxy coatings does not change in the presence of hydrotalcite This demonstrates that the newly formed coatings retains the properties of the epoxy coatings + SEM images The SEM images of epoxy with HTM, HTMS and HTMGS were observed by SEM (Figure 3.35) Fig 3.35: SEM images of epoxy coatings with 3% HTM (a), 3% HTMS (b) and 3% HTMGS (c) The SEM image observation showed that all coatings had leafy structures of hydrotalcite With epoxy coatings containing HTM, the hydrotalcite particles were clumped With epoxy coatings containing HTMS, the HTMS particles were dispersed evenly in the epoxy substrate, size about 200-300 nm With epoxy coatings containing HTMGS, the HTMGS particles were well dispersed in the epoxy substrate, with a particle size of 100-400 nm But the dispersion was less than that of the HTMS particles + Determine the basic distance of HTM, HTMS and HTMGS in epoxy coating by XRD 23 Fig 3.36: XRD pattent of epoxy coatings (a), epoxy coatings with % HTM (b), % HTMS (c) and % HTMGS (d) The results showed that the surface modification by silane increased the dispersibility of HTM in epoxy These results were consistent with the results of the above SEM analysis 3.2.3.2 Evaluation of corrosion protection of epoxy containing HTM, HTMS and HTMGS by electrochemical impedance The impedance diagrams of coatings after after 35 days immersion in 3% NaCl solution is shoawn in Fig 3.37 Fig 3.37: The Nyquist plots after 35 days immersion in 3% NaCl solution of epoxy coatings (a), epoxy coatings with % HTM (b), % HTMS (c) and % HTMGS (d) The impedance results showed that, after 35 days of immersion, the electrolyte had reached the steel surface with epoxy sample and epoxy sample containing 3% of HTM, so the corosion process had occurred While with epoxy samples containing HTMS and HTMGS, the electrolyte penetrated the coatings, but not to the metallic surface, the corrosion process of metal had not yet occurred Fig 3.38: The Rf variation vs Fig 3.39: The Z10mHz variation vs immersion time in 3% NaCl solution immersion time in 3% NaCl solution of epoxy (o), epoxy with 3% HTM of epoxy sample (o), epoxy with 3% (□), 3% HTMS (♦) and 3% HTMGS HTM (□), 3% HTMS (♦) and 3% (●) HTMGS (●) The analysis results of the Rf value and the impedance modulus value at 10 mHz frequency of the sample according to immersion time 24 (Fig 3.38, Fig 3.39) show that the presence of HTM, HTMS and HTMGS increased the barrier properties and corrosion resistance of the epoxy coatings and the modification by silane enhances the effect of HTM Modification of HTM by APS gives higher efficiency than modification by GS 3.2.3.3 Mechanical properties of epoxy coatings with HTM, HTMS and HTMGS Table 3.18: Adhesion and impact resistance of waterborne epoxy coatings with HTM, HTMS and HTMGS Samples Adhesion (N/mm2) Impact resistance (Kg.cm) EW0 2.0 180 EW- HTM 2.3 180 EW- HTMS 4.5 180 EW-HTMGS 4.0 180 The results show that surface modification of HTM with APS has higher adhesion than GS Increase of adhesion of HTMS can be explained by the role of silane at interface between the coating/steel The results of adhesion measurements are also consistent with the results of the impedance measurements 3.2.3.4 Salt spray test Fig 3.40: Photographs of steel surface coated waterborne epoxy coatings (a), with HTM (b), HTMS (c) and HTGS (d) after 96 h salt spray test with 3% NaCl solution The results of the salt spray test (Fig 3.40) of the samples showed that HTM modification with silane increased the corrosion protection of the epoxy coatings The HTMS is more effective than HTMGS This result is consistent with the results of impedance measurement 3.2.3.5 Corrosion protection mechanism of waterborne epoxy coatings with HTM, HTMS and HTMGS Hydrotalcite bearing molypdate is surface-modified with APS or GS silane, thus enhancing the dispersion of hydrotalcite bearing corrosion inhibitor in paint film This is explained in section 3.1.3.5 and is perfectly consistent with the result of HTMS and HTMGS dispersion in epoxy 25 coatings was demonstrated by SEM images, X-ray diffraction and IR spectra in section 3.2.3.1 On the other hand, the presence of HTMS and HTMGS will significantly increase the adhesion of the epoxy coatings ( the result in section 3.2.3.3) This can be explained that the modified hydrotalcite has the ability to adsorb onto the surface of the metal, thus increasing the bonding capacity between the epoxy and the metal surface Thus, the presence of HTMS and HTMGS in the waterborne epoxy coatings increases shielding ability and corrosion resistance of the film Especially when the paint film is defective, under the effect of aggressive environment (Cl- anion), hydrotalcite bearing molypdate corrosion inhibitor in the paint film will occur ion exchange reactions As a result, the molypdate will be released from hydrotalcite to protect the carbon steel and Cl- ions will be retained in the hydrotalcite structure The corrosion protection mechanism of the epoxy coatings containing hydrotalcite bearing molypdate corrosion inhibitor is shown in Figure 3.41 Fig 3.41: The corrosion protection mechanism of the epoxy coatings containing hydrotalcite bearing molypdate corrosion inhibitor Summary of Section 3.2 Successful synthesis of hydrotalcite with molypdate (HTM) and its surface modified by N-(2-aminoethyl)-3-aminopropyltrimethoxisilane (HTMS) or 3-glycidoxipropyltrimethoxisilane (HTMGS) The HTM, HTMS and HTMGS have a particle size of 50-200 nm Electrochemical measurement results show that they are anode corrosion inhibitors, and corrosion inhibitor performance achieved 92.8 %, 95.5 % and 95.3 %, respectively, at a concentration of g/L in 0.1 M NaCl solution Their presence has significantly increased the protective performance and adhension of the waterborne epoxy coatings The surface modification with silane has the effect of increasing dispersibility, thus enhancing the reinforcing effect of hydrotalcite bearing molypdate inhibitor in epoxy coatings The HTM modified by N-(2-aminoethyl)-3-aminopropyltrimethoxisilane has more reinforcing effect than that 3-glycidoxipropyltrimethoxisilane 26 CONCLUSION Hydrotalcite intercalated with benzothiazolylthiosuccinic acid corrosion inhibitor (HTBA) was successfully synthesized by coprecipitation method (in a N2 atmosphere, at 650C, pH=8-10) and its surface was modified by N-(2-aminoethyl)-30 aminopropyltrimethoxisilane (at 60 C) (HTBAS) The analysis results show that HTBA and HTBAS have a particle size of 50-200 nm with benzothiazolylthiosuccinic acid content over 30% Electrochemical measurements results show that they are anodic corrosion inhibitors, and inhibition efficiency achieves 96% at a concentration of g/L in ethanol/water (2/8) solution contain 0.1 M NaCl Solventborne epoxy coating with 3% hydrotalcite bearing benzothiazolylthiosuccinic acid and 3% hydrotalcite bearing benzothiazolylthiosuccinic acid modified by N-(2-aminoethyl)-3aminopropyltrimethoxisilane were prepared for corrosion protection of carbon steel The evaluation results of the corrosion protection by the method of impedance, s alt spray test and adhension test showed that the presence of HTBAS has significantly increased the protection performance of the solventborne epoxy coatings The surface modification with silane has the effect of increasing dispersibility in epoxy, thus enhancing the reinforcing effect of hydrotalcite bearing benzothiazolylthiosuccinic acid inhibitor in epoxy coatings Hydrotalcite intercalated with molypdate (HTM) was successfully synthesized by co-precipitation method (in a N atmosphere, at 650C, pH=8-10) and its surface modified by N-(2aminoethyl)-3-aminopropyltrimethoxisilane (HTMS) or 30 glycidoxipropyltrimethoxisilan (HTMGS) (at 60 C) HTM, HTMS and HTMGS have a particle size of 50-200 nm with molypdate content over 12% Electrochemical measurement results show that HTM, HTMS and HTMGS are anodic corrosion inhibitors, and inhibition efficiencies achieve 92.8 %, 95.5 % and 95.3 %, respectively, at a concentration of g/L in 0.1 M NaCl solution Waterborne epoxy coating with 3% hydrotalcite bearing molypdate and 3% hydrotalcite bearing molypdate modified by N-(2-aminoethyl)-3aminopropyltrimethoxisilane or 3-glycidoxipropyltrimethoxisilane were prepared for corrosion protection of carbon steel Their presence has significantly increased the protective performance and adhension of the waterborne epoxy coatings The surface modification with silane has the effect of increasing dispersibility in epoxy, thus enhancing the reinforcing effect of hydrotalcite bearing molypdate inhibitor in epoxy coatings The 27 HTM modified by N-(2-aminoethyl)-3-aminopropyltrimethoxisilane has more reinforcing effect than that 3-glycidoxipropyltrimethoxisilane 28 LIST OF WORKS HAS BEEN PUBLISHED Nguyen Thu Trang, Nguyen Tuan Anh, To Thi Xuan Hang, Trinh Anh Truc Synthesis and Characteristic of hydrotalcite bearing corrosion inhibitor Molypdate Vietnam Journal of Chemistry 51 (6ABC) (2013) 364-367 Nguyen Tuan Anh, To Thi Xuan Hang, Trinh Anh Truc, Bui Van Truoc, Nguyen Thuy Dương Modification of hydrotalcite bearing molybdate by 2aminoethyl-3-aminopropyltriethoxy silane and applied in waterborne epoxy coating Journal of Nanoscience and Nanotechnology 53 (1A) (2015) 138-145 To Thi Xuan Hang, Nguyen Tuan Anh, Trinh Anh Truc, Bui Van Truoc, Thai Hoang, Dinh Thi Mai Thanh, Siriporn DaopisetSynthesis of 3- glycidoxipropyltrimethoxisilane modified hydrotalcite bearing molybdate as corrosion inhibitor for waterborne epoxy coating Journal of Coatings Technology and Research 13 (2016) 805-813 Nguyen Tuan Anh, Ngo Thi Hoa, To Thi Xuan Hang, Nguyen Thuy Dương, Trinh Anh TrucInfluence of hydrotalcite containing corrosion inhibitor modified by silane on corrosion protection performance of epoxy coating VNU Journal of science: Natural sciences and technology 33(4) (2017) 1-7 ... corrosion inhibitors and fabrication of nanocomposite coatings for corrosion protection of carbon steel This work contributes to the development of metal anti -corrosion protection coatings The... in epoxy coatings 3.2 Synthesis of hydrotalcite bearing molypdate modified by silane and applied in watertborne epoxy coatings for corrosion protection of carbon steel 3.2.1 Synthesis and structural... coating - Synthesis of hydrotalcite bearing molydate modified by silane and applied in waterborne epoxy coating for corrosion protection of carbon steel: + Synthesis and structural analysis of hydrotalcite