Dr. Luz Marina Calle earned her Ph.D. in chemistry from Ohio University and shortly thereafter became a professor of chemistry at Randolph College in Virginia. In 1989, she was selected to participate in NASA’s Summer Faculty Fellowship program at the Kennedy Space Center (KSC). Her summer work at KSC continued for a decade while performing her duties as professor and chair of the chemistry department at Randoph College. In 2000, Dr. Calle joined NASA permanently. She now leads NASA’s Corrosion Technology Laboratory at KSC.
NASA Tech Briefs: Dr. Calle, you currently head up NASA’s Corrosion Technology Laboratory, which was formally established in 1985 at the Kennedy Space Center. Tell us about the Corrosion Technology Laboratory and the types of projects you typically get involved with.
Dr. Luz Marina Calle: NASA began corrosion studies at KSC in 1966 during the Gemini/Apollo Programs when KSC’s Beachside Atmospheric Exposure Test Site was established to evaluate coatings and maintenance procedures for the corrosion protection of carbon steel. The facility is still being used today and is available to customers outside NASA.
In 1985 we introduced other techniques to look at corrosion in addition to long-term atmospheric exposure. We introduced the use of electrochemical techniques that allow us to look at corrosion on a faster scale. In 2000, we became NASA’s Corrosion Technology Laboratory where, in addition to corrosion testing, we incorporated an applied research capability to develop technologies that provide a solution to NASA’s corrosion-related problems. These technologies will also have applications outside NASA and will be made available for commercialization.
The types of projects that we typically get involved with depend on the needs of our customers. We find ourselves in the position where, very often, our customers don’t even know that the problems they’re having are corrosion-related. A recent example involved the corrosion failure of the stainless steel that was selected to fabricate flex hoses and tubing. These materials were selected for their high resistance to corrosion, but failed at the launch pad and we had to find alternate materials. Another problem occurs when the commercial production of coatings that we use for corrosion protection is discontinued. This usually happens in response to stricter environmental regulations. So we’ll get a call asking, “What do we do now?”
We’re working on a project right now that’s aimed at identifying a corrosion protection coating for flexible hoses that carry fluids under cryogenic conditions. It’s a challenging project because we have unique conditions here and it’s not easy to identify something that is commercially available off the shelf. As a result, we are developing “smart coatings” for corrosion detection and protection, but I can tell you more about that later.
Basically, we support NASA’s KSC mission of launching in one of the most corrosive environments in the world.
NTB: Not only is the environment corrosive, but the high heat levels and acids generated during a space shuttle launch add to the problem. What is it about the exhaust gasses from the solid rocket boosters that makes them so corrosive?
Dr. Calle: The solid rocket boosters generate a very corrosive exhaust that consists mainly of alumina particles and about 70 tons of hydrochloric acid. There are no coatings that can withstand the direct impact of the highly corrosive exhaust from the solid rocket boosters. Coating selection for the corrosion protection of the pad is based on different zones classified in terms of solid rocket booster exhaust deposition: zone 1 receives direct rocket engine exhaust impingement, zone 2 includes surfaces that experience elevated temperatures and acid deposition, and zone 3 includes areas outside those of zones 1 and 2. This environment is very unique to NASA and is something that we will need to deal with for as long as we use solid rocket boosters to launch.
NTB: The problem of corrosion around the launch facilities is apparently so bad that in July 2001 NASA published a standard called “NASA Standard 5008 – Protective Coating of Carbon Steel, Stainless Steel, and Aluminum On Launch Structures, Facilities, and Ground Support Equipment.” Tell us about the creation of that standard and how successful it’s been in helping to combat the problem.
Dr. Calle: The standard was developed to establish uniform engineering practices and methods across NASA, and to ensure the inclusion of essential criteria in coatings on launch structures, the ground support equipment, and facilities. There are other standards out there – ASTM as well as the military – but nobody encounters the same corrosive conditions that we have here at KSC.
The standard divides the pad into the different zones of exposure previously described in order to define coating system requirements for surfaces located in specific environments. In addition, the standard includes a description of required materials, equipment, safety, quality assurance, and testing procedures to qualify coatings for inclusion in the qualified products list that is part of the standard. So, in order to be included in that qualified products list, the coatings are evaluated for initial acceptance following an exposure period of 18 months at KSC’s beachside atmospheric exposure test site. The coatings must maintain their high level of corrosion protection performance for a period of 5 years to remain on that qualified products list. Application characteristics must be judged acceptable prior to atmospheric exposure testing.
We are continuously testing coatings to keep the qualified products list up to date and also perform periodic revisions of the standard. One of the challenges we have is with the depletion of the number of coatings in the qualified products list due to progressively stricter environmental regulations that limit the number of coatings that are commercially available. For this reason, we’re constantly testing new coatings and are now in the process of developing new ones.
NTB: Do spacecraft experience the same kind of corrosion problems in space, or in a lunar environment, that they do on Earth?
Dr. Calle: No. That type of corrosion is something that we are still learning about. In order to fully answer that question, it’s necessary to think in terms of what we mean by corrosion. Corrosion is defined as the degradation of a material that results from its interaction with the environment. All materials corrode eventually, but some do it faster than others. Most people are familiar with the corrosion of metals such as iron and structural carbon steel. When materials corrode they lose their structural integrity.
If we focus on the corrosion of metals, an important condition for corrosion is humidity, or the presence of water. You also need an electrical connection between the material that is corroding, or losing integrity, and the material that is accepting the electrons that the metal is losing. So, if you think in terms of corrosion in outer space, for example on the moon, where we know there is no humidity, you would not expect corrosion as we know it to occur there. However, there are several concerns dealing with corrosion inside a habitat where there would be humidity. One concern involves corrosion in water purification systems. But out in the open, in the vacuum, there’s little concern at the moment, based on what we know. However, there have been some experiments exposing materials to the outer space environment that indicate that the presence of atomic oxygen causes erosion of some materials and can also be damaging to coatings. There’s also high-energy radiation, such as UV radiation that causes material degradation, but this is different from what we think of as corrosion on Earth.
NTB: One of the pioneering technologies that your group is involved with – and you mentioned it earlier – is something called “smart coatings,” which are coatings that incorporate healing agents that can detect and repair damaged areas. How do smart coatings work, and how close do you think you are to making that technology commercially viable?
Dr. Calle: This is a technology that we are very excited about. The term “smart” or “intelligent” coating, in general, is applied to a coating that knows what to do, where to do it, and it does it on its own without external intervention. The technology for the smart coatings is similar to what the human body does in response to a wound. The body deploys a response to heal it. The smart coating we are developing contains microcapsules that have been designed to break and deliver their core corrosion control components when corrosion starts, or healing agents when the coating suffers mechanical damage such as a scratch.
NTB: Like a clotting agent in blood?
Dr. Calle: Exactly. Here, at NASA, our laboratory pioneered the invention of microcapsules that respond to corrosion. We have a patent application on this NASA technology. We realized that corrosion sends signals when it starts that a coating can use to deploy a response. So, we came up with the idea of a microcapsule that has a wall that responds to the changes that take place when corrosion starts. More specifically, our microcapsule responds to the pH change. When corrosion starts, the pH increases in that area and our microcapsule – a walled microcapsule – breaks when the pH increases. So, this microcapsule is perfect for us because, for example, on the launch pad the acid from the solid rocket boosters won’t damage the microcapsule, but when corrosion starts and the pH increases, becoming more basic, the microcapsule will break and release its content.
We designed these microcapsules to be able to signal the onset of corrosion by delivering a corrosion indicator that will change color. This will facilitate maintenance of the facilities because if you see a bright colored spot, you’ll know that corrosion is starting there and you can do something about it before it’s too late. But the intelligence of the coating won’t stop there. It will also deploy corrosion inhibitors to prevent the corrosion from becoming a problem. So this corrosion sensitive microcapsule is really the “brain” of the smart coating.
Our next step – we are in the early stages of that – is to encapsulate healing agents that will be released if you damage the coating, not by corrosion but by mechanical damage such as what happens with a scratch. In this case, microcapsules loaded with healing agent will break open and release the components that will combine on the surface of the bare metal to form a film that will recover the exposed surface. To give you an example, when you buy two-part epoxy at the store, you need to mix the two components to form a hard bonding compound. In our case the components will be separated in the coating and will mix as a result of the scratch.
NTB: So someday, possibly, if I get a scratch on my car, it will heal itself before rust can begin. Is that what you’re saying?
Dr. Calle: That’s the idea. As a matter of fact, it’s interesting that you mention that because we know that Honda Motors is interested in our technology. Coatings for corrosion protection are very important to the automobile industry.
NTB: Launch Complex 39B is about to undergo a complete redesign to accommodate the Ares I launch vehicle. How involved is the Corrosion Technology Lab in that project right now?
Dr. Calle: We are very involved with that. We actually have two projects. One is the smart coatings development project. We did a lifecycle cost analysis and determined that these smart coatings are going to make the launch pad more sustainable and safer at a lower cost.
The other project is involved with finding an alternate refractory material for protection of the flame trench at the launch pad. I don’t know if you have heard about the failures in the flame trench where the refractory material has been ejected. We have lost fire bricks from that wall. This happened during STS-124. Basically, that’s a problem that the shuttle has been coping with and that is getting worse and worse, so our laboratory is currently working on developing an alternate material to that Apollo-era material that’s been there for a long time and for which the failures are becoming greater, more frequent, and more costly. The space shuttle program has recently approved some funding to instrument the flame trench. We’re going to install sensors there to characterize the environment for the remainder of the shuttle flights to gather information that will guide us in our effort to provide alternate refractory materials for Constellation. So we’re working on those – smart coatings and alternate refractory materials for the flame trench.
NTB: Your group also works with NASA’s Acquisition Pollution Prevention (APP) Program to study coatings and materials that might prove harmful to the environment. How do you balance the need for corrosion protection under extreme conditions with the need to protect the sometimes fragile ecosystem, and does one ever take precedence over the other?
Dr. Calle: Well, it’s interesting that you asked this question because, as you probably know, this is something where there’s always a tradeoff. Just for the record, the APP program is now called TEERM – Technology Evaluation for Environmental Risk Mitigation. They’re interested in environmental risk mitigation and that’s one of the driving forces in corrosion technology development because many of the coatings and procedures that work very well to prevent corrosion are now known to be harmful to humans and the environment.
So, what we do in our technology development efforts is that we rule out everything that is known to be toxic. We’re taking care of that at the development stage, because it doesn’t make sense to use something that we know is toxic. For example, one of the major contributors to pollution in corrosion control is sandblasting of painted structures, because many of them contain harmful components such as lead and heavy metals. The smart coating we are developing will, hopefully, eliminate or at least decrease the frequency for total replacement. Pollution prevention is something that is very important to us and it’s something that we always need to be aware of. As a result of this, the coating industry in general is moving in the direction of eliminating volatile organic compounds in paints and finding alternatives for harmful corrosion inhibitors such as the chromate conversion coatings that have been used for the corrosion protection of aerospace aluminum alloys. NASA’s TEERM has supported testing in our lab to find chromate free coatings.
NTB: What would you say has been the most challenging project ever undertaken by the Corrosion Technology Laboratory?
Dr. Calle: I think the two that we are engaged in right now for the Constellation program: the smart coatings and the alternative refractory materials for the flame trench. Again, these are very unique technologies that address specifically a corrosion problem that NASA has, so there’s very little out there that we can use. We are getting very comfortable with the development of the smart coatings, but we still have a great deal to learn about the refractory materials. The refractory materials that are used by industry don’t face the harsh conditions that we face here, such as acid solid rocket booster exhaust, huge temperature fluctuations, vibration, constant humidity, and water deluge that affect the performance of the refractory concrete at the launch pad. Refractory materials are normally used in industry under dry conditions, such as they exist in a furnace. But here at KSC, those materials get wet all the time and, as they degrade, they hold more water, and that water in the pores expands when the temperature increases. As a result, you have all the ingredients for a failure of the material. These conditions are very challenging to us right now, but we are excited and confident about these two projects.
NTB: The Corrosion Technology Lab is one of those unique groups at NASA that not only spins off the technology it develops to commercial entities, you actually sell your services and expertise to companies that need to do research and testing in this area. Please tell us how that program works.
Dr. Calle: Our team includes NASA civil servants and contractors. Our contractor is Arctic Slope Regional Corporation (ASRC) and their contract with NASA allows them to use our laboratories and facilities, on a non interfering way, to do work for others. So they can work directly with industry and academia. This means that the lab is available to everyone who needs our services for a fee that depends on the labor and materials involved.
NTB: How much of what the Corrosion Technology Lab has learned over the years would you say has already found its way into the commercial sector?
Dr. Calle: The Corrosion Lab has not been involved in technology development for very long, but there’s a liquid galvanic coating for the protection of rebars in reinforced concrete that is commercially available now. We are hoping that the smart coatings will be commercially available in three to four years down the road. And in that regard, we are partnering with industry in order to help us get there sooner rather than later.
NTB: Finally, you once said that the cost associated with corrosion in the U.S. comes to more than $300 billion per year, and that at least one-third of that cost could be eliminated at the design stage. What did you mean by that?
Dr. Calle: Traditionally, engineers – specifically design engineers – have not been trained to take corrosion into account at the designing stage, so what has happened in the past is that corrosion is not a factor until there’s a failure. The cost of corrosion could be lowered by taking corrosion into account when designing a structure.
What I mean by that is that you have to know the corrosivity of the environment where that structure is going to be built so that you can select the appropriate materials and corrosion protection. For example, a bridge here in Florida is exposed to different conditions from those of a bridge in the desert or from those of a bridge in the north where they use deicing salts. So the environment has to be taken into account. We at Kennedy are an example of that. Early in the 1960s when the space program started, they did not know how corrosive this environment was and learned the hard way. But nowadays we know more about corrosion and take it into account. If you select the right material for corrosion performance, then you’re going to save on maintenance down the road. If you select the right coating, that will also save you money.
You can also avoid corrosion by building a structure in such a way that water doesn’t collect in some areas and by avoiding putting dissimilar metals together. This can be illustrated by a problem we have here in our building with a solar collector on the roof that is corroding away because it was designed and manufactured for use in a desert in California, so when you bring it here to Florida it corrodes badly. I went to take a look the other day, and one of the first things that I noticed was a rim where water collects. It has the right conditions there for corrosion, and one of the things that I suggested was to drill some holes to drain that area and avoid the accumulation of water.
So, if you can keep humidity low; if you design in such a way that you don’t have hidden areas; if you don’t put dissimilar metals together where you have a galvanic couple; if you look around as you become aware of corrosion; you can think of many ways where corrosion problems could have been avoided if you had selected the right screw to attach the metal. I see that all the time. I even see it around my house, where they used the wrong screws and they’ve corroded.
NTB: It creates a galvanic cell, right?
Dr. Calle: Exactly. There are many things you can do at the design stage that will save maintenance costs down the road and will also make structures safer.
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