Clay Culture: Hypersonic Travel

A new type of ultra-high temperature ceramics may help us travel five times faster than the speed of sound.

Imagine flying from New York to Los Angeles in about a half hour—that fantasy may soon become a reality.

Researchers have been working to develop hypersonic travel for several years, but there are still many hurdles and challenges to be overcome. To travel at hypersonic speed means going five times the speed of sound, or 3836 miles per hour—otherwise known as Mach 5.

Scientists in collaboration with NASA have already developed a concept plane with a rocket engine capable of speeds up to Mach 3. And more recently, the US and Australia finished testing hypersonic planes for defense purposes.

But hypersonic travel isn’t ready for prime time just yet. One reason is the loud sonic boom that results from traveling faster than the speed of sound, which can damage eardrums. Researchers are still working on that issue.

But another problem exists with the heat generated by the plane as it reaches those high velocities. When an aircraft travels that fast, temperatures around the plane can quickly heat up to 3632–5432°F (2000–3000°C). Hot air and gas surrounding the plane as it torpedoes through the atmosphere can erode the plane’s surface. Those processes, called oxidation and ablation, can destroy the plane’s structure, causing the surface to pull away from the metal underneath.

This is where ultra-high temperature ceramics (UHTCs) come in to play. UHTCs are materials with melting points above 3000°C that are used in extreme environments, such as rockets and defense missiles, to keep surfaces from disintegrating at high temperatures. But now, even some UHTCs apparently aren’t up to the task of protecting aircraft from high temperature extremes.

A concept plane. Photo: The University of Manchester.

But there may be a new material on the horizon. Researchers at The University of Manchester, Royce Institute, and Central South University have developed a carbide coating that is stronger than zirconium carbide (ZrC), a UHTC typically used in tool bits.

“…One of the biggest challenges is how to protect critical components such as leading edges, combustors and nose tips so that they survive the severe oxidation and extreme scouring of heat fluxes that such temperatures cause during flight,” Philip Withers, University of Manchester professor and research team member, says in a news release.

“Current candidate UHTCs for use in extreme environments are limited and it is worthwhile exploring the potential of new single-phase ceramics in terms of reduced evaporation and better oxidation resistance,” lead researcher Ping Xiao explains in the release.

The team used a process called reactive melt infiltration to create a Zr0.8Ti0.2C0.74B0.26 coating and then reinforced it with a carbon-carbon composite. They discovered the resulting coating was twelve times superior to ZrC and more resistant to high temperatures.

According to the paper’s abstract, “The sealing ability of the ceramic oxides, slow oxygen diffusion, and a dense and gradient distribution of ceramic result in much slower loss of protective oxide layers formed during ablation than other ceramic systems, leading to the superior ablation resistance.”

So, perhaps we can someday look forward to having lunch in LA after a morning of shopping in New York, after we solve that sonic-boom dilemma.

The paper, published in Nature Communications, is “Ablation-resistant carbide Zr0.8Ti0.2C0.74B0.26 for oxidizing environments up to 3000 °C” (DOI: 10.1038/ncomms15836).

the author Faye Oney, is a content marketing specialist and editor for the Ceramic Bulletin and the Ceramic Tech Today (http://ceramics.org/category/ceramic-tech-today) blog at the American Ceramic Society. She is a 20-year marketing and communications veteran, specializing in writing and social-media strategy.

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