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Morphology and Protection Mechanisms of Epoxy-silane Anti-Corrosion Coatings

Wang, Peng
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1246997365

Abstract Details

2009, PhD, University of Cincinnati, Engineering : Materials Science.
The film structure and surface morphology of a novel one-step epoxy-silane coating system were revealed by neutron reflectivity, Atomic Force Microscope (AFM) and Environmental Scanning Electron Microscope (ESEM). The bis-sulfur silane is enriched at the coating-substrate interface instead of uniformly distributed, which leads to a layered structure. The phase separation within bulk coating films was investigated by Ultra Small Angle X-ray Scattering (USAXS) and Small Angle Neutron Scattering (SANS). The epoxy-silane network forms branched morphologies without significant interface. No phase separation on scale range from 0.5 nm to 10.3 nm were observed. The protection mechanisms of the epoxy-silane coating system were studied in terms of coating structure, water response behavior, salt exclusion and hydrothermal stability. By comparing pure epoxy and epoxy-silane mixtures in various aqueous environments, the effects of the addition of silane were determined. The key mechanisms of silane-enhanced protection are: 1. Bis-sulfur silane is enriched at the substrate-coating interface and forms a SiO2-like interface region, which ensures excellent adhesion between coating and substrate. The addition of silane also increases the roughness of the epoxy-silane film. 2. The silane serves as a crosslinker, resulting in a denser and less hydrophilic bulk film compared to the neat epoxy. The hydrophobic nature of bis-sulfur silane also increases the overall hydrophobicity of the mixed film. 3. The salt exclusion effect is introduced to epoxy-silane film due to the addition of bis-sulfur silane fines the molecular-level free space. 4. The epoxy-silane film shows improved hydrothermal stability. The addition of bis-sulfur silane eliminates the hydroxyl groups formed during the cure process. The absence of hydroxyl group prevents the bond scission effect. The addition of silane also introduces the immunity of hydrothermal degradation to the film-substrate interface by the formation of SiO2-like interface layer. The hydrothermal degradation behavior of bis-type silane films were studied by NR. The key factors determining the hydrothermal stability were evaluated by comparing the hydrothermal degradation behaviors of series of bis-silane films varying in bridging group (bis-sulfur/bis-amino/mixture of bis-sulfur and bis-amino), curing temperature (80-°C/180-°C) and thickness (~20 nm /~1000 nm). A thick bis-sulfur silane film (>1000 nm) is robust under 80-°C liquid H2O conditioning, while bis-amino silane film degrades anyway. The bis-amino silane also introduces vulnerability to mixed silane films. As a promising chromate replacement and an effective pigment in a ‘superprimer’ coating system, vandate inhibitor (V) films were studied by NR in terms of film structure, speciation and water barrier. The V film has a layered structure and is not hydrated. When treated with saturated water vapor, the water wets the air-side surface and penetrates the entire film. The absorbed water is harbored in the pre-existing molecular-level free space. However, when treated at elevated temperature or liquid water, the film becomes thinner but denser, which is preferred for inhibition applications.
Dale Schaefer (Committee Chair)
Jude Iroh (Committee Member)
Vesselin Shanov (Committee Member)
William Vanooij (Committee Member)
194 p.
Engineering; Materials Science
Coating; epoxy; silane; hydrothermal degradation; neutron reflectivity; x-ray reflectivity; surface; interface; converstion coating; corrosion

Recommended Citations

Citations

  • Wang, P. (2009). Morphology and Protection Mechanisms of Epoxy-silane Anti-Corrosion Coatings [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1246997365

    APA Style (7th edition)

  • Wang, Peng. Morphology and Protection Mechanisms of Epoxy-silane Anti-Corrosion Coatings. 2009. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1246997365.

    MLA Style (8th edition)

  • Wang, Peng. "Morphology and Protection Mechanisms of Epoxy-silane Anti-Corrosion Coatings." Doctoral dissertation, University of Cincinnati, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1246997365

    Chicago Manual of Style (17th edition)

ucin1246997365
526
© 2009, all rights reserved.
This open access ETD is published by University of Cincinnati and OhioLINK.