Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.
Issue link: http://mp.epubxp.com/i/468598
18 MARCH 2015 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 54, NO. 3 MATERIAL MATTERS Microscopic beads detect corrosion, deliver healing payload, and present visible warning that corrosion is occurring S cientists with Battelle (Columbus, Ohio) have developed microscopic beads that can detect corrosion forming on a metal substrate, deliver a payload to heal damage caused by the corrosion, and provide an early warning sign that corro- sion is present. The beads, 30- to 50-µm diameter spherical capsules f illed with a liquid healant, resemble a f ine, whitish powder in bulk and are designed to be mixed into coatings that protect critical infrastructure from corrosion. When corrosion is present, the beads' surfaces undergo a chemical reaction that causes them to f luoresce (which can be seen with an ultraviolet [U V] light), then break apart and release a healing agent. The f luorescence is a prompt indicator to maintainers that corrosion has initiated and provides them with the opportunity to mitigate the underlying problem early on, while the healant immediately repairs the corrosion damage and slows the corrosion process. The timely discovery and remediation of corrosion can result in signif icant time and cost savings as well as improved structural reliability. Early detection of a corrosion problem is the challenge that researchers were looking to address with this technolog y, says Ramanathan Lalgudi, senior research scientist with Battelle. Corro- sion can initiate and develop for a while before it can be visually detected, he notes, and by then it can require exten- sive repairs to f ix the damage. About 10 years ago, Lalgudi and his colleagues at Battelle started working on this nano- technolog y. At the time, the researchers were developing functional nanomateri- als by attaching groups of chemicals to the surface of materials and studying their effectiveness. This led to the idea of using the same technical approach to determine if corrosion products on a metal substrate would react with func- tional nanomaterials so that corrosion could be detected. From there, the researchers developed a single microbead that is capable of detecting corrosion and providing a warning sign that corrosion is present, and also simultaneously releas- ing a liquid that will mitigate the corro- sion damage. Ty pically, most other self- healing coating technologies either require two separate microcapsules— one that contains a healing agent and another that holds the catalyst to activate it—or the microcapsules do not release the payload via a corrosion-triggered release mechanism, says Lalgudi. The microbead developed by Lalgudi's team comprises a polymer shell that sur- rounds a core f illed with a proprietary liq- uid healant. The shell is compatible with epoxy and poly urethane coatings ty pi- cally used for corrosion protection of metallic substrates, and is resilient under applied pressure but able to easily break open and release the healant when corro- sion is detected. 1 An organic functional group with a complexing agent that binds to metal ions is incorporated into 5 to 8% of the shell wall. Several complexing agents can be used, Lalgudi notes, but the scientists selected one that will capture and bind to iron and aluminum ions. Dur- ing the corrosion process, metal ions are released from the surface of the metal. As the ions encounter a microbead in the coating, the complexing agent on the sur- When added to a coating, the microbeads will fuoresce in UV light and release a self-healing agent when exposed to metal corrosion byproducts. Photo courtesy of Battelle.