Monday, January 6, 2014

E-NEWS: High Temperature, High Performance

By Charlie Feigenoff

Pass Elizabeth Opila’s laboratory in the evening, and you can see her equipment glow. That’s because Opila, an associate professor of materials science and engineering, is interested in the response of materials to hot and reactive conditions. And when Opila says hot, she means it. She and her students are heating materials to as high as 2,000˚C.

“Regardless of the material, our approach is similar,” she says. “We try to understand what happens to a material as it gets hot, predict how long it will survive and determine how we can make it better.”

Quite naturally, this area of research interests jet engine manufacturers. They would like to replace many of the metal components of engines with the latest ceramic matrix composites (CMCs), which can withstand higher temperatures. “There could be a huge payoff for adopting CMCs,” Opila says. “Engines with CMCs would be much lighter, run hotter and be significantly more efficient.”

But there are a number of obstacles that must be overcome first — and Opila is addressing a series of them. CMCs must be able to withstand the corrosive effect of water vapor produced during combustion at the high temperatures and air speeds found in jet engines. With funding from Rolls-Royce, Opila has built a device that simulates this environment and is testing the effect of steam at high temperatures and velocities on different CMC materials. She hopes to discover those underlying characteristics that enable some CMCs to outperform others.

The corrosive effect of sodium sulfate, a byproduct of jet engine combustion in marine environments, is another issue. Opila is investigating its effect on CMCs with a grant from the Office of Naval Research. In addition, she is conducting research sponsored by the Air Force Academy on the glass that can form inside CMCs at high temperatures. “The glass could attack the weight-bearing fibers used to reinforce CMCs,” Opila says. “We are trying to understand the factors that lead to its formation.”

Opila’s expertise in testing and analyzing materials in extremely hot environments has applications for the thermal protection of aircraft — particularly hypersonic aircraft — as well as propulsion. Hypersonic vehicles rush through the atmosphere at speeds in excess of Mach 5. As they do so, they generate a shock wave that subjects their leading edges to extreme temperatures. Opila is trying to understand how a class of ultra-high temperature ceramics will respond in these circumstances. “Their oxidation behavior is not really well defined,” she says. “We are trying to understand these materials at a basic level.” This project has received funding from NASA and the Air Force Office of Strategic Research.

But not all of Opila’s research involves ultra-high temperatures, aircraft or ceramics. She is studying how ferritic steels might perform as interconnects in solid oxide fuel cells. “These interconnects are very thin, and they are exposed to water vapor in a reactive environment,” she says. “We need to know if they can withstand oxidation and last the required 60,000 hours.”

Although Opila is a dedicated materials scientist, her work is not motivated solely by a desire to understand new materials. Rather, she is also inspired by the things these new materials might enable engineers to accomplish. “If we can find materials that work at high temperatures and in extremely reactive environments, we will enable huge performance improvements for power and propulsion technologies,” she says.