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Understanding corrosion protection mechanisms of nanocomposite polymer coatings on carbon steel: A combination of in-situ AFM and electrochemical studies
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.ORCID iD: 0000-0001-5007-2705
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.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2015: 53
Keyword [en]
Polymer coatings, electrochemistry, nano, in-situ AFM, mechanism, corrosion protection
National Category
Chemical Engineering
Research subject
Chemistry; Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-175348ISBN: 978-91-7595-669-5 (print)OAI: oai:DiVA.org:kth-175348DiVA: diva2:860448
Public defence
2015-10-30, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
EU, FP7, Seventh Framework Programme, 263262
Note

QC 20151013

Available from: 2015-10-13 Created: 2015-10-12 Last updated: 2016-12-05Bibliographically approved
List of papers
1. EIS and in situ AFM study of barrier property and stability of waterborne and solventborne clear coats
Open this publication in new window or tab >>EIS and in situ AFM study of barrier property and stability of waterborne and solventborne clear coats
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2014 (English)In: Progress in organic coatings, ISSN 0300-9440, E-ISSN 1873-331X, Vol. 77, no 3, 600-608 p.Article in journal (Refereed) Published
Abstract [en]

Various processes can occur when paints are in contact with moisture, such as ingress of water and aggressive ions into the coating. As a consequence, the microstructure and properties of the paints can be affected. The present study combines electrochemical impedance spectroscopy (EIS) and in situ atomic force microscopy (AFM) to investigate the barrier property of waterborne and solventborne coatings on mild steel, paying particular attention to the occurrences in the first 24 h after contact between the coating surface and electrolyte. The sequential in situ AFM images revealed that changes on the order of hundreds of nanometres at the coating surface have occurred shortly after the exposure to the electrolytes. EIS observations for the clear waterborne alkyd coating revealed a rise in the |Z|0.015Hz and a decrease in the coating capacitance after a few hours of exposure. Evidences that water uptake caused swelling of the coating and promoted the closure/blockage of pores were given by means of in situ AFM. The solventborne alkyd emulsion has demonstrated lower reactivity to the presence of the electrolyte and a correlation between the coating resistance and defects/pores evolution is suggested.

Keyword
AFM, EIS, Organic coatings, Topography
National Category
Other Chemistry Topics
Identifiers
urn:nbn:se:kth:diva-142340 (URN)10.1016/j.porgcoat.2013.11.024 (DOI)000331919800006 ()2-s2.0-84893418431 (Scopus ID)
Funder
EU, European Research Council
Note

QC 20140228

Available from: 2014-02-28 Created: 2014-02-28 Last updated: 2017-12-05Bibliographically approved
2. In-Situ AFM and EIS Study of Waterborne Acrylic Latex Coatings for Corrosion Protection of Carbon Steel
Open this publication in new window or tab >>In-Situ AFM and EIS Study of Waterborne Acrylic Latex Coatings for Corrosion Protection of Carbon Steel
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2015 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 162, no 1, C55-C63 p.Article in journal (Refereed) Published
Abstract [en]

Corrosion protection for carbon steel by three waterborne styrene-acrylic latex coatings with different glass transition temperature (Tg) and levels of hydrophobicity has been studied by in-situ atomic force microscope (AFM) and electrochemical impedance spectroscopy (EIS) measurements in 3.0 wt% NaCl solution. The AFM images reveal the micro-and nano-structure of and pinholes in the coatings as well as their changes during exposure in the solution, whereas the EIS spectra vs. time of exposure show the barrier property, stability and degradation of the coatings. The coating with crosslinking and high level of hydrophobicity exhibited a high barrier property and long-term corrosion protection in the solution despite of some shallow pinholes. The coating without crosslinking but having high Tg and high level of hydrophobicity also displayed a high barrier property and certain stability although initial changes occur in the solution. However, for the coating without crosslinking and with low Tg and relative low level of hydrophobicity, some dissolution and open-up of defects occurred on the surface shortly after exposure and the coating lost its barrier property rapidly in the solution. The reasons for the different behaviors between the coatings are discussed with respect to the crosslinking, Tg and the hydrophobicity level of the coating.

National Category
Corrosion Engineering
Identifiers
urn:nbn:se:kth:diva-160057 (URN)10.1149/2.0851501jes (DOI)000345979700050 ()2-s2.0-84923376621 (Scopus ID)
Funder
EU, FP7, Seventh Framework Programme, SteelCoat 263262
Note

QC 20150305

Available from: 2015-03-05 Created: 2015-02-13 Last updated: 2017-12-04Bibliographically approved
3. In Situ AFM and Electrochemical Study of a Waterborne Acrylic Composite Coating with CeO2 Nanoparticles for Corrosion Protection of Carbon Steel
Open this publication in new window or tab >>In Situ AFM and Electrochemical Study of a Waterborne Acrylic Composite Coating with CeO2 Nanoparticles for Corrosion Protection of Carbon Steel
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2015 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 162, no 10, C610-C618 p.Article in journal (Refereed) [Artistic work] Published
Abstract [en]

The corrosion protection of a waterborne acrylic composite coating with 1 wt% ceria nanoparticles (CeNP) coated on carbon steel in 3 wt% NaCl solution was investigated by ex-situ and in situ as well as electrochemical atomic force microscopy (AFM) observations, combined with open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) measurements. The synthesized CeNP were stabilized by acetic acid. The transmission electron microscopy characterization showed fine nano-size of as-synthesized CeNP, the ex-situ AFM imaging revealed uniform dispersion of the CeNP in the composite coating and greatly reduced nano-sized pinholes in the coating. The in situ and electrochemical (EC) AFM investigations indicate release of some CeNP and aggregates from the coating surface and then precipitation of some particles and cerium-compounds during the exposure. The OCP and EIS results demonstrated that the addition of 1 wt% CeNP leads to a significantly improved long term barrier type corrosion protection of the waterborne acrylic composite coating for carbon steel in 3 wt% NaCl solution. The beneficial effect of the CeNP is attributed to the blocking of nano-sized defects and inhibition by the cerium compounds originated from the acetic acid stabilized CeNP.

Keyword
Acrylic coating, Ceria nanoparticle, Corrosion protection, EIS, In-situ and EC-AFM
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-172358 (URN)10.1149/2.0071512jes (DOI)
Note

QC 20150825

Available from: 2015-08-19 Created: 2015-08-19 Last updated: 2017-12-04Bibliographically approved
4. In-situ AFM and EIS study of a solventborne alkyd coating with nanoclay for corrosion protection of carbon steel
Open this publication in new window or tab >>In-situ AFM and EIS study of a solventborne alkyd coating with nanoclay for corrosion protection of carbon steel
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2015 (English)In: Progress in organic coatings, ISSN 0300-9440, E-ISSN 1873-331X, 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.

Keyword
Alkyd coating, Corrosion protection, EIS, In-situ AFM, Nanoclay
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-172356 (URN)10.1016/j.porgcoat.2015.06.003 (DOI)000360596300023 ()2-s2.0-84938316178 (Scopus ID)
Funder
EU, FP7, Seventh Framework Programme, SteelCoat 263262
Note

QC 20150820

Available from: 2015-08-19 Created: 2015-08-19 Last updated: 2017-12-04Bibliographically approved
5. In-situ AFM and Electrochemical AFM Investigation of Corrosion Protection of Solventborne Alkyd: Polyaniline Composite Coating for Carbon Steel
Open this publication in new window or tab >>In-situ AFM and Electrochemical AFM Investigation of Corrosion Protection of Solventborne Alkyd: Polyaniline Composite Coating for Carbon Steel
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(English)Manuscript (preprint) (Other academic)
National Category
Corrosion Engineering
Identifiers
urn:nbn:se:kth:diva-175365 (URN)
Note

QS 2015

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

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