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In-situ AFM and EIS study of a solventborne alkyd coating with nanoclay for corrosion protection of carbon steel
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.ORCID iD: 0000-0001-5007-2705
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2015 (English)In: Progress in organic coatings, ISSN 0300-9440, Vol. 87, 179-188 p.Article in journal (Refereed) [Artistic work] Published
Abstract [en]

A solventborne alkyd composite coating containing modified montmorillonite (MMT) nanoclay was made on carbon steel, and its corrosion protection was investigated by in-situ atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS) measurements in 3 wt.% NaCl solution. X-ray diffraction (XRD) analysis indicated intercalation of the MMT sheets in the composite coating. Thermo-gravimetric analysis (TGA) demonstrated improved thermal stability of the composite coating due to the modified nanoclay. Scanning electron microscopy (SEM) and AFM examination revealed dispersion and also some aggregation of the nanoclay particles in the coating. In-situ AFM images show a stable coating surface at nano-scale during relative long time exposure in the NaCl solution, indicating an enhanced stability of the composite coating. The EIS results confirmed that the composite coating provides an enhanced barrier type corrosion protection for carbon steel in the corrosive solution, which could be attributed to the intercalated lamellar MMT sheets in the coating that block the defects and decrease the transport of water and corrosive species.

Place, publisher, year, edition, pages
2015. Vol. 87, 179-188 p.
Keyword [en]
Alkyd coating, Corrosion protection, EIS, In-situ AFM, Nanoclay
National Category
Chemical Sciences
URN: urn:nbn:se:kth:diva-172356DOI: 10.1016/j.porgcoat.2015.06.003ISI: 000360596300023ScopusID: 2-s2.0-84938316178OAI: diva2:847254
EU, FP7, Seventh Framework Programme, SteelCoat 263262

QC 20150820

Available from: 2015-08-19 Created: 2015-08-19 Last updated: 2015-10-13Bibliographically approved
In thesis
1. Understanding corrosion protection mechanisms of nanocomposite polymer coatings on carbon steel: A combination of in-situ AFM and electrochemical studies
Open this publication in new window or tab >>Understanding corrosion protection mechanisms of nanocomposite polymer coatings on carbon steel: A combination of in-situ AFM and electrochemical studies
2015 (English)Doctoral thesis, comprehensive summary (Other academic) [Artistic work]
Abstract [en]

Corrosion protection of carbon steel is crucial in today’s world and there is an urgent need to replace the hazardous compounds used with environmentally friendly anticorrosion coatings. In this European collaborative research project, new types of functional composite anticorrosion coatings for steel were developed with properties beyond the state-of-the-art using nanotechnology. The corrosion protection properties of waterborne (WB) acrylic and solventborne (SB) alkyd anticorrosion coatings are combined with special ceria nanoparticles (CeNPs), nanoclay and polyaniline (PANI). The corrosion protection mechanisms of these new coating systems in a corrosive environment of 3 wt. % NaCl solution have been explored. In this work, a WB acrylic coating with high hydrophobicity and low emission of volatile organic compounds (VOC), and a WB composite coating with the addition of acetic acid stabilized CeNPs were developed. An advanced surface functionalization was used to make the CeNPs compatible with the WB matrix and to achieve improved corrosion protection for carbon steel. A SB compositealkyd coating with high solids content and the addition of dimethyl dehydrogenated tallow ammonium chloride modified nanoclay, and another one with sulfonic acid doped emeraldine salt (ES) form of PANI were also developed, taking into account of the compatibility between the additives and the polymer matrix.

Scanning electron microscopy (SEM) and transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were utilized for characterization of the these coatings. Ex-situ and in-situ atomic force microscopy (AFM) was employed to study the stability and activity of the nanoparticles in the nano-structured latex in these coatings. Electrochemical controlled (EC)-AFM and cyclic voltammetry (CV) were used to study the occurrence of active redox reactions in the nanoparticle additive in the acrylic and alkyd composite coatings. In combination, open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) were used to study the long-term corrosion protection behavior of these coatings. The corrosion protection mechanisms of the developed coating systems were revealed by a combination of AFM and electrochemical techniques. The key results and conclusions can be summarized as follows:  

   The WB acrylic coating with crosslinking was shown to be a stable barrier protection against corrosion for carbon steel in the 3 wt. % NaCl solution, which can be attributed to its high level of hydrophobicity and the compact structure with densely packed latex nanoparticles.

   The improved corrosion protection of the WB composite acrylic coating with 1 wt. % CeNPs in the NaCl solution was attributed to the uniform distribution of the CeNPs in the composite coating and the re-deposition of the insoluble cerium compounds, impeding the penetration of water and corrosive ions into the metal surface. 

   The enhanced corrosion protection of the SB composite alkyd coating with 3 wt. % nanoclay was attributed to the intercalation of the nanoclay with the laminar structure in the polymer matrix that decreased water penetration.

   The redox reaction peaks in the CV and the changes of the PANI aggregates under the applied potentials observed in the EC-AFM revealed the active corrosion protection mechanism of the 1 wt. % PANI in the SB composite alkyd coating. The PANI appears to have passivated the metal surface by a redox reaction between the ES and leuco emeraldine base (LB) forms of PANI during exposure to the NaCl solution.

   In short, our study has demonstrated the improved corrosion protection properties and revealed the protection mechanisms of the new nanocomposite coatings for carbon steel. Thus, with the environmentally-friendly anticorrosion coatings developed in this project it will be possible to reduce the use of toxic and hazardous substances in and to reduce the release of VOCs from anticorrosion coatings. Furthermore, this work has opened up the possibility for using nanoparticles in the development of organic coatings for corrosion protection of metal.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. xiv, 49 p.
TRITA-CHE-Report, ISSN 1654-1081 ; 2015: 53
Polymer coatings, electrochemistry, nano, in-situ AFM, mechanism, corrosion protection
National Category
Chemical Engineering
Research subject
Chemistry; Chemistry
urn:nbn:se:kth:diva-175348 (URN)978-91-7595-669-5 (ISBN)
Public defence
2015-10-30, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
EU, FP7, Seventh Framework Programme, 263262

QC 20151013

Available from: 2015-10-13 Created: 2015-10-12 Last updated: 2015-10-13Bibliographically approved

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