Researchers at the University of Missouri-Rolla have received $450,000 from the Air Force Office of Scientific Research for the continued study of ultra-high temperature ceramics.
Dr. Bill Fahrenholtz and Dr. Greg Hilmas, both associate professors of materials science and engineering at UMR, are studying zirconium-diboride-based ceramics that can withstand temperatures up to 3,000 degrees Celsius. These ceramics could be used to keep hypersonic vehicles from burning up as they fly.
“Our work is applicable to the development of missiles with a global reach,” Fahrenholtz says. “The nose, the leading and trailing edges, and the propulsion section of hypersonic vehicles would be exposed to the most heat.”
While ceramics are much more heat-resistant and oxidation-resistant than common metals, researchers must find the right elemental combinations to use for applications involving ultra-high temperatures.
As part of the funded project at UMR, students heat ceramic powders like zirconium diboride up to 2,100 degrees Celsius while compressing them to make a dense ceramic. They then slice the solid material and evaluate its performance capabilities under simulated atmospheric conditions that might be associated with a hypersonic environment.
“These hypersonic vehicles are just test vehicles right now or simply on the drawing board,” says Hilmas. “It is expected that they will exit and re-enter the atmosphere as they are gliding toward their intended target.”
Fahrenholtz and Hilmas were previously interested in the further development of technology used in making ceramic tiles for reusable launch vehicles similar to those in the current space shuttle program. Space shuttle vehicles have 22,000 glass-coated ceramic tiles for protection against heat during reentry. Those tiles, as currently constituted, can withstand temperatures up to 1,350 degrees Celsius. The nose and front edges of a shuttle’s wings get the most exposure to dangerously high temperatures.
Although much attention has been paid to the performance of the space shuttle tiles in the past, that probably won’t be an area of high concern for NASA, or for Hilmas and Fahrenholtz, in the future.
“We’re going back to Apollo-style lunar missions,” Hilmas explains. “The push is to go back to the moon and then on to Mars by 2020. They won’t need a reusable reentry vehicle like the shuttle in the decade ahead. NASA is looking to use capsules with a shield that erodes some as it is heated. For that, they can use carbon-based material instead of the dense ceramics we’re developing at UMR.”
The materials Hilmas and Fahrenholtz are currently working with are for sleek, high performance vehicles with sharper edges. These missiles and other hypersonic aerospace vehicles would need more heat protection over longer periods of time than the space shuttle or Apollo-style capsules.
For the hypersonic vehicles to work, the sharp edges and propulsion components would have to be protected by ceramic materials like those engineered at UMR.
“The sharper leading edges mean the vehicles have more maneuverability and can basically glide at much higher altitudes during reentry,” Hilmas says. “If you want to go to sharper leading edges on hypersonic vehicles, you’re going to have to go with materials with higher melting temperatures.”