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Corrosion Fighters Develop Microscopic Tools
Luz Marina Calle at an electron microscope. Luz Marina Calle looks over microcapsules using an electron microscope at the Space Life Sciences Laboratory at NASA's Kennedy Space Center in Florida. The microcapsules are too small to see with the naked eye, so researchers use the high-powered microscope to study their formation. Photo credit: NASA/Jim Grossmann
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Luz Marina Calle, Jerry Buhrow and Wendy Li Luz Marina Calle, Jerry Buhrow and Wendy Li are part of the team researching microcapsules for use in fighting corrosion. Calle is the NASA lead investigator and principal investigator at NASA's Corrosion Technology Laboratory. Photo credit: Jim Grossmann
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Microcapsules as they look under electron microscope. A look at microcapsules as seen through the ultra-powerful lens of an electron microscope at NASA's Corrosion Technology Laboratory at Kennedy.

Metal samples are tested outdoors for corrosion. The Corrosion Technology Laboratory tests metals and coatings in part by subjecting them to the natural environment at NASA's Kennedy Space Center in Florida. The salt air, heat, ultraviolet light and humidity make the area extremely corrosive for metals. Unprotected materials last about six months in the conditions, which is why the space agency is researching protection methods. Photo credit: NASA/Steve Siceloff

Luz Marina Calle and her team are developing a new weapon to ward off rust and corrosion on metals. If it works, Kennedy's launch pads, structures and NASA spacecraft will be better protected. So will cars, bridges, balconies and pretty much anything else that has metal in it.

The weapon is a microcapsule and when filled with the right chemicals, it will show exactly where corrosion is occurring and how severe it is. It also can protect against further corrosion and in some cases will be able to heal the damage.

It sounds like a tall order for a tiny structure too small to see with the naked eye. The microcapsule's strength comes from its numbers. Millions of them can be embedded in paint or other covering material. The chemicals stay safely inside the capsules until something breaks them open.

The capsules are tailored to break open when rust begins to form. Then the protection agents spread out and the metal healers can go to work. To draw attention to the corrosion, some of the microcapsules would be filled with material that changes the color of the affected area. Just as rust shows where it is occurring, the chemical would highlight corrosion, but without the damage.

"This is (Kennedy Space Center) developed technology," Calle said. "No one imagined you could use these capsules for corrosion control."

Perhaps it should not be a surprise that such innovation would come from a place some consider one of the most corrosion-prone in the world.

Calle leads a team of about a dozen scientists and engineers who make up NASA's Corrosion Technology Laboratory at Kennedy. It turns out Kennedy is the perfect place to study corrosion because it happens so quickly and with an intensity not found anywhere else in the world.

NASA chose to place its primary launch center on Florida's Atlantic coast for a host of reasons, including launch safety, orbital mechanics and because Florida doesn't typically freeze in the winter. There wasn't much thought given to corrosion.

"Corrosion loves salt, humidity, heat and ultraviolet light and that's what we have here," Calle said.

Other parts of the world offer high levels of one or two categories, but Kennedy is unique because it has high levels in all categories.

Kennedy also subjects its structures to rocket exhaust, particularly the acidic residue from the space shuttle's solid rocket boosters. That's what did in what was thought to be a corrosion-resistant material, stainless steel.

"Traditionally, stainless steel is highly corrosion resistant, but you put that same stainless steel at the pad and it's gone, it just disappears," Calle said.

The practical effect of having such a severe threat is that it demands research and solutions.

That's why she applied to NASA as soon as she had the chance. With a background and Ph.D. in physical chemistry, she was teaching chemistry courses at a Randolph College in Virginia when she saw a flyer about NASA opportunities.

"I applied immediately," she said. Calle began working here in 1989, but there wasn't a dedicated corrosion research lab. That came from a reorganization in 2000 that established it as an area of applied research.

The agency had small-level research, including a test site with exposure racks for samples near the beach close to Launch Pad 39A. The site is still used today and no coating is approved for use at NASA without first going through 18 months on the test stand to prove it can handle the environment.

But today's research is far more extensive. It includes equipment such as salt fog chambers and electrochemical cells that can stress a metals or coatings as severely as natural conditions, but much faster. That allows researchers to move ahead with promising ideas and move on from those that don't work well.

Some of the samples put up in the 1960s are still there, accompanied by a parade of other materials and coatings as they are developed and tested.

The ones that are still there are those protected by zinc coverings. But zinc can be considered bad for the environment, so researchers don't want to use more of it than is needed. Again, this is an opportunity for microcapsules. If the zinc can be contained inside microcapsules, it will only be released where it is needed, limiting its environmental impact.

After researching better coatings, Calle said the team decided to seek "smart coatings." That led to the discoveries about microcapsules and how to use them for corrosion resistance. There has been great progress, but more steps await refinement.

The coverings with microcapsules inside have not been used yet in a large scale, so the coatings used on new structures at Kennedy, such as the mobile service tower built for a next-generation launcher, still use a zinc-based covering. That's why the tower structure looks light gray.

The microcapsules also are a technology that could be applied to just about anything. NASA is focusing on the structures like service towers and the Vehicle Assembly Building. Spacecraft, too, are considered candidates for corrosion prevention.

Auto companies have contacted Calle about her research because they like the idea of a paint that would actively inhibit rust on their cars. Construction companies are intrigued by the possibility of covering structural metal with "smart coatings" that can prevent corrosion. With the microcapsules in place, designers could be confident that corrosion is being prevented. Plus, when inspections are needed, detection would be easier.

That kind of interest tells Calle that her team's applied research and development is likely to reach far beyond NASA.

Steve Siceloff
Kennedy Space Center