Professor Zhiyong (Richard) Liang and research faculty member Ayou Hao hold pieces of carbon fiber reinforced polymer composites with a protective heat shield made of a carbon nanotube sheet that was heated to 1,900°C.
Photo credit: Mark Wallheiser, FAMU-FSU College of Engineering

Life spans of carbon fiber reinforced polymer composites (FRP) in the structures of satellites, rockets, and jet aircraft are limited by how they handle heat.

Florida Agricultural and Mechanical University-Florida State University (FAMU-FSU) College of Engineering researchers from FSU’s High-Performance Materials Institute (HPMI) are developing a heat shield design that better protects these structures.

“Flight systems are becoming more and more high-speed, even going into hypersonic systems, which are 5x the speed of sound,” says HPMI Director Richard Liang. “When you have speeds that high, there’s more heat on a surface. Therefore, we need a much better thermal protection system.”

Carbon nanotubes, linked hexagons of carbon atoms in the shape of a cylinder, form the heat shields. Sheets of those nanotubes – also known as buckypaper – have incredible abilities to conduct heat and electricity. By soaking the buckypaper in a resin made of a phenol compound, the researchers were able to create a lightweight, flexible material that is also durable enough to potentially protect the body of a rocket or jet from the intense heat it experiences in flight.

Existing heat shields are often very thick compared to the base they protect, says Ayou Hao, a research faculty member at HPMI.

After building heat shields of varying thicknesses, the researchers put them to the test.

One test involved applying a flame to the samples to see how they prevented heat from reaching the carbon fiber layer they were meant to protect. The researchers then bent the samples to study their strength.

They found the samples with sheets of buckypaper were better than control samples at dispersing heat and keeping it from reaching the base layer. They also stayed strong and flexible compared to control samples made without nanotube protective layers.

That flexibility is helpful, making the nanotubes less vulnerable to cracking at high temperatures compared to ceramics, a typical heat-shield material. They’re also lightweight, which helps engineers improve aircraft fuel economy.

The project received second place among peer-reviewed posters at the 2019 National Space and Missile Materials Symposium and received third place at the Society for the Advancement of Material and Process Engineering 2019 University Research Symposium.

That recognition is helpful for showing the United States Air Force Office of Scientific Research, which partially supported the work, the promise of further research, Hao says.

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