A team of scientists at Florida State University's High-Performance Materials Institute is using advanced nanomaterials to produce lightweight heat shields that can stand up to the impact of hypersonic speeds. Based on sheets of carbon nanotubes called "buckypaper," the new experimental shields can be made into a very thin, flexible skin that can be applied to airframes to both protect and support them.
For aircraft and spacecraft operating in the atmosphere at speeds above five times the speed of sound, heat shields are a necessity if the vehicle is to avoid severe damage at the very least. This is especially true today when many aerospace designs rely increasingly on carbon composites that provide strength and lightness, but are vulnerable to high temperatures.
Heat shields made of phenol plastics have been around since the 1950s. Known as ablative heat shields, these protect a returning spacecraft by burning away in layers, carrying away the excess heat. Unfortunately, these shields are bulky, inflexible, and have to be replaced after a single use. In the 1970s, the US Space Shuttle used a ceramic heat shield that absorbed and re-radiated heat to protect the craft. These tiles could be reused, but they were still bulky, rigid, and brittle as well.
As an alternative, the Florida State team is looking at buckypaper, which is made by taking carbon nanotubes (tube-shaped carbon molecules 50,000 times thinner than a human hair) and pressing them into sheets. When compressed into layers the paper is 10 times lighter but up to 500 times stronger than steel.
To make a heat shield, the buckypaper is soaked phenol resin to form a light, flexible material. It's very thin, yet so strong that it can help to support the aircraft's structure. When subjected to flame tests, the buckypaper samples kept their strength and flexibility while dispersing heat away from the base layer underneath the shield at temperatures of up to 1,900° C (3,450° F).
The research was published in Carbon.
Source: Florida State University
