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Coating Signals Corrosion Colorfully

Friday, October 18, 2013

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A new corrosion-sensing coating that incorporates nanocapsules would flag underlying corrosion by changing colors, researchers say.

The polymer coating includes nanocapsules that contain a pH-indicating agent, which is able to indicate when corrosion starts under the coatings. The nanocapsules can be placed in different layers of the coating, or used as a single layer system.

When corrosion starts, the nanoreactors change color in the corrosive areas, According to the researchers, these indicators are not released from the mesoporous nanocarriers, preventing leaching.

Corrosion sensing coatings
Photos: IOP Publishing

New coating technology would detect corrosion and turn colors in the affected area, researchers say. Pictures of coated substrates doped with Si NC-PhPh and tested during three days in 0.5 M NaCl: (a) and (b) coated aluminum allow with artifical scribe, (c) and (d) coated magnesium alloy without scribe.

The research team from the University of Aveiro in Portugal is led by Mikhail Zheludkevich, a senior researcher in the Department of Materials and Ceramics Engineering. The research, "Nanocontainer-based corrosion sensing coating," was published Sept. 17 in the online edition of Nanotechnology.

Beyond Self-Healing

"The corrosion sensing can be considered as independent functionality of a protective coating or can also be considered as an important additional functionality which can complement the self-healing coatings," Zheludkevich told Nanowerk.

Corrosion sensing in a self-healing coating would detect when the coating is no longer able to heal defects, Zheludkevich noted.

"For example, the new coating developed by our group in collaboration with several European partners from academic and industrial sectors is counting on the multi-level self-healing effect based on 'smart' nanocontainers.

The coatings were developed as part of the European project MUST (Multi-Level Protective Materials for Vehicles by 'Smart' Nanocontainers).

"The main idea is that several mechanisms of self-healing can be integrated in the same coating providing effective active protection which is proportional to the external impacts such as corrosive attack and mechanical impacts," Zheludkevich said.

self healing coatings

The coating includes nanocapsules that contain an agent that is able to indicate when corrosion starts underneath. The nanocapsules can be placed in different layers of the coating, or used as a single layer system.

The research team used a colorless crystalline silica, phenolphthalein, in mesoporous silica nanocontainers with a goal of accomplishing a color change signal when there was a pH change near the nanocontainer.

"With the onset of corrosion, pH increases in the local cathodic areas due to the formation of hydroxide ions whilst acidification often occurs at anodic sites as a result of hydrolysis reactions," Zheludkevich explained.

"The respective pH variations can be used to detect and locate the active corrosion spots in confined defects of the coatings or under the coatings if pH indicators are incorporated in a polymer protective layer."

Developments in Self-Healing

In the last few years, several advances have been made in self-healing coatings and nanotechnology.

Researchers in Germany developed a method of multilayer anticorrosion protection using self-healing nanotechnology as an alternative to toxic chromium, Nanowerk reported in 2008. The multi-level system provides a barrier to external impacts while also responding to changes in the internal structure.

Last year, Nanowerk reported the development of an encapsulation system based on a sonochemically formed porous metal layer that doesn't have to be immobilized on the surface of the substrate or be incorporated into the protective coating layer. The system offered protection against biological and chemical agents.


Tagged categories: Coating Materials; Corrosion; Corrosion protection; Nanotechnology; Research; Self-healing

Comment from Daniel Grossmann, (10/18/2013, 11:37 AM)

Can the coating be applied with airless spray at pressures up to 3,000 PSI? I'm asking because other encapsulated nanocontainers will break with this type of application. How about conventional spray at 60 PSI? Do the capsules survive this application?

Comment from Jodi Temyer, (10/18/2013, 2:41 PM)

PaintSquare News has reached out to the study's author and is waiting for a response.

Comment from Jodi Temyer, (10/21/2013, 4:28 PM)

Mikhail Zheludkevich, who led the research, responds: “The tests with high pressure spraying were not conducted in frame of this study. However the developed nanocontainers are composed by spherical mesoporous inorganic nanoparticles which are very different when compared to conventional polymer capsules. The mechanical properties of silica carriers are significantly above those of the polymer shells. It hardly imaginable that these mesoporous particles will break even at such high pressures. Moreover if the particles are partially broken it does not mean that they stop functioning since the active sensing molecule will be still kept in mesopores.“

Comment from Daniel Grossmann, (10/22/2013, 9:09 AM)

I'm glad to hear you're considering the applications. I look forward to hearing more about progress in your research.

Comment from Liliana Rodríguez, (10/22/2013, 5:26 PM)

I would like to know if the coating coulb be applied in aircrafts

Comment from Mikhail Zheludkevich, (10/23/2013, 1:32 PM)

The original driving force of this research was the aeronautical applications. Therefore AA2024 was used as one of the substrates for testing the sensing effect.

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