The mythical edge of hypersonic vehicles has arrived and it is the work of researchers like Erica Corral that will fuel their growth and space exploration.
The U.S. Department of Defense research arm Defense Advanced Research Project Agency (DARPA), did a test launch of a hypersonic technology vehicle last month. The vehicle is designed to reach speeds of Mach 20 – more than 15,000 miles per hour. Unfortunately, nine minutes after launch, communications were lost with the craft.
At hypersonic speeds – above Mach 5 – the temperature is extreme and a highly sophisticated thermal protection system is necessary to protect these aircrafts.
“Hypersonic vehicles have to withstand roughly 30 seconds of temperatures above 2,800 degrees Celsius (5,072 degrees Fahrenheit),” Corral said. “That is followed by what you call the cruise period of flight which would be a sustained 20 to 30 minutes at temperatures around 1,300 to 1,800 degrees Celsius (2,372 to 3,272 F).”
That’s where Corral comes in.
An assistant professor at the University of Arizona, Corral, 32, established her lab in August 2008. Its where she conducts research on ultra-high temperature ceramics (UHTCs) and composites, UHTC coatings, high-temperature ceramic nanocomposites and oxide ceramic composites.
Corral researched ceramics as an undergraduate and graduate student.
“The class of materials I was really excited to research and spend time on were materials that could withstand high temperature extremes, because there is a lot that is unknown about their behavior in these types of extreme environments,” Corral said. “So couple that with very sophisticated applications for these materials and it just drew me into the field.”
Having an aptitude and skill in a field she loves has translated into some early-career recognition for Corral.
She is the first UA researcher to receive the Air Force’s Young Investigator Award and also was awarded a National Science Foundation Early Career Award both to fund research she is conducting in these fields.
Her work for the Air Force involves research in multilayer ultra-high temperature coatings for oxidation protection of carbon-carbon composites under extreme hypersonic conditions.
Current hypersonic vehicles use ablative coatings to protect them, which means that the coatings vaporize at high temperatures. This hinders the ability for multiple missions from a single aircraft. Corral said she believes there is the potential for longer missions in more extreme environments if UHTCs are used.
“However, the response of UHTCs under hypersonic flight conditions is not well understood, thus limiting some Air Force missions,” Corral said.
Her previous research already indicates that no single coating material offers enough protection, so Corral is investigating the oxidation of multilayer and composite ceramic coatings. She will study her developments on thermal analysis equipment and for test time on a sophisticated solar thermal test facility that can duplicate hypersonic flight heat-flux environments.
Her National Science Foundation award funds a research and education program that will investigate novel microstructures of ultra-high temperature composites and laminate structures using spark plasma sintering in order to understand their fundamental oxidation behavior at high temperature.
Spark plasma sintering is a process of densification of a ceramic powder into a solid. It works by passing a DC current through the material creating the heat internally as opposed to standard methods which require an external heating source.
“This is especially advantageous for the ultra high temperature ceramics we’re working with because they are highly covalently bonded materials,” she said. “In order to consolidate them, they have to be heat treated to 2000 degrees Celsius in order to be converted from a powder to a dense crystalline material system.”
While other machines in the field would take hours to get to temperature, require hours at temperature to make the conversion and still need hours to cool down, Corral’s spark plasma sintering machine from Thermal Technology can conduct the whole run in 15 minutes.
“That’s the exciting part about being in this field right now,” Corral said. “Everything is coming together right now. We actually have the technology that we need to make some of these material systems – both the novel equipment to create these samples but the analytical equipment to probe and learn more about the microstructures. There is enough interest from our government and within our industry for these materials. So a lot of need-based research dollars are being invested into what we’re doing. I expect we’re going to see a lot happening in our field in a much shorter amount of time.”
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