ALBUQUERQUE, N.M. — Researchers at the Department of Energy’s Sandia National Laboratories have developed a new lightweight material to withstand ultra-high temperatures on hypersonic vehicles, such as the space shuttle.
The ultra-high-temperature ceramics (UHTCs), created in Sandia’s Advanced Materials Laboratory, can withstand up to 2000ºC (about 3,800ºF).
Ron Loehman, a senior scientist in Sandia’s Ceramic Materials, said results from the first seven months of the project have exceeded his expectations.
“We plan to have demonstrated successful performance at the lab scale in another year with scale-up the next year,” Loehman said.
Thermal insulation materials for sharp leading edges on hypersonic vehicles must be stable at very high temperatures (near 2000ºC). The materials must resist evaporation, erosion, and oxidation, and should exhibit low thermal diffusivity to limit heat transfer to support structures.
Composite materials UHTCs are composed of zirconium diboride (ZrB2) and hafnium diboride (HfB2), and composites of those ceramics with silicon carbide (SiC). These ceramics are extremely hard and have high melting temperatures (3245ºC for ZrB2 and 3380ºC for HfB2). When combined, the material forms protective, oxidation-resistant coatings, and has low vapor pressures at potential use temperatures.
“However, in their present state of development, UHTCs have exhibited poor strength and thermal shock behavior, a deficiency that has been attributed to inability to make them as fully dense ceramics with good microstructures,” Loehman said.
Loehman said the initial evaluation of UHTC specimens provided by the NASA Thermal Protection Branch about a year ago suggests that the poor properties were due to agglomerates, inhomogeneities, and grain boundary impurities, all of which could be traced to errors in ceramic processing.
During the first seven months, the researchers made UHTCs in both the ZrB2 and HfB2 systems that are 100 percent dense or nearly so. They have favorable microstructures, as indicated by preliminary electron microscopic examination. In addition, the researchers have hot pressed UHTCs with a much wider range of SiC contents than ever before. Availability of a range of compositions and microstructures will give system engineers added flexibility in optimizing their designs.
Money spent to fund basic research in materials science does more to advance the cause of space exploration and space travel than money spent operating the Space Shuttle and International Space Station. The development of new materials will eventually help enable the development of much more advanced launch vehicles and spacecraft. Also, nanotech advances promise eventually to enable the construction of a space elevator. Far too much government money is spent doing things in space in the short term that would be better spent pursuing scientific and technological advances that would enable us to do orders of magnitude more in the long term.
|Share |||Randall Parker, 2003 October 17 01:19 PM Materials Advances|