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Smart Coating Incorporated with Inhibitor-Enclosed Nanocontainers for Corrosion Protection of Steel

Ebrahim Fathabadi, Hadi | 2021

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  1. Type of Document: Ph.D. Dissertation
  2. Language: English
  3. Document No: 54736 (57)
  4. University: Sharif University of Technology, International Campus, Kish Island
  5. Department: Science and Engineering
  6. Advisor(s): Ghorbani, Mohammad
  7. Abstract:
  8. In this thesis a smart anticorrosive pH-responsive coat was developed with layer by layer (LbL) technique in the assembly of SiO2/CTAB/PSS/HMTA/PSS/PEI/PSS. SiO2 nanoparticles were prepared from Matland Company (Iran) with average size of 24 nm. At first, the corrosion inhibition of HMTA for API 5L Grade B steel in 3.5 wt.% NaCl solution was investigated. Tafel polarization technique showed the optimum concentration of HMTA was 0.08 M with 92% corrosion inhibition efficiency as the morphology of coverage and adsorption on the steel surface was confirmed by SEM and EDS. AFM results showed the roughness of the surface decreased from 241 nm to 56 nm that is attributed to HMTA adsorption on the steel surface in the solutions without and with the concentration of 0.08 M HMTA, respectivelty. Thermodynamical parameters showed that the adsorption is physical and obeys Longmuir isotherm. Later, smart multilayered pH-responsive nanocontainers were synthesized by LbL process and their characteristics were studied. EDS analysis and elemental mapping were applied to investigate the uniformity of layers deposition in each stage of the LbL process by elements concentration tracking. Zeta-potential measurements were done to insure surface potential changing in each stage of the LbL process. FTIR technique was used to determine the functional groups, bonds, and structures in the prepared nanocontainers. The amount of the loaded inhibitors in the nanocontainers was measured during the thermal decomposition of HMTA by TGA and SIMS. The pH-sensitivity of nanocontainers was investigated by polarization technique. Tafel polarization was applied in 3.5 wt.% NaCl solutions with or without 1 wt% HMTA-loaded nanocontainers, in various pH values (pH=2, 5, 7, 9, 12), and different immersion times (12, 24 and 36 hours). The results showed the successful deposition, uniformity of each layer and proper electrostatic bonding among them in LbL process. The amount of the loaded inhibitors in the nanocontainers was 2.86 wt.%. It is found that after 36 h immersion of nanocontainers in 3.5 wt.% NaCl solutions with different pHs, the maximums smart releasing of corrosion inhibitor in the solutions were 79.3% and 78.9% which were related to pH=2 and pH=12, respectively. Finally, smart nanocontainers were doped in the epoxy coating applied on the surface of mild steel and the uniform dispersivity, thermal stability, and corrosion resistance were investigated by elemental mapping, TGA/DSC, and EIS techniques, respectively. The results showed the uniform dispersion of nanocontainers in epoxy and no alteration in epoxy characteristics after doping nanocontainers. EIS results confirmed an increase in the corrosion resistance of epoxy, after 5, 10, 15, 20, 25, and 30 days immersion in 3.5 wt.% NaCl solution with doping concentrations of 3, 6, and 9 wt.% nanocontainers, which was attributed to smart releasing of corrosion inhibitor to protect the steel surface. Furthermore, mechanism and kinetic model of corrosion inhibitor releasing from nanocontainers were studied
  9. Keywords:
  10. Smart Coating ; Inhibitor ; Mild Steel ; Corrosion ; Layer by Layer (LbL)Technique ; Nanocontainer ; Anticorrosive Coating

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