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Composite fiber can protect firefighters from extreme heat

Firefighter clothing, spacecraft insulation and coatings for buried detectors could all benefit from a new thermal insulation material developed by scientists in China and the United States. The team has demonstrated that its ceramic airgel has superior thermal insulation to materials currently used for these applications.

Ceramic aerogels are ultra-porous materials, made up of thin layers of ceramic that separate small pockets of air. A typical ceramic airgel is 99% air. Ceramic barriers prevent convective heat transfer between air bubbles, which means these materials can act as thermal insulators. There is a problem, however – ceramics are generally brittle, which can lead to catastrophic failure when the material is stressed.

To overcome this, the scientists fabricated a zirconium(IV) silicate nanofiber airgel with a zigzag architecture that is considerably more mechanically stable than previously reported ceramic aerogels.

build for strength

The scientists used a multi-step manufacturing method. First, they used an electrospinning method to turn a zirconium-silicon starting material into a cotton candy-like ceramic felt. Then, he mechanically folded this felt in a zigzag. Finally, they sintered the zigzag construction at 1100°C.

The resulting ceramic airgel construction absorbs mechanical stress, preventing it from fracturing under stress. It does this by preventing the fibers of the material from sliding past each other when stretched, as you would expect. Instead, the fibers are bent under tension, with the expansion of the fibers running in one direction being counterbalanced by the contraction of the fibers running in the other direction. This design means that the structure is very stable mechanically.

Another aspect of the material’s design means that it can block heat radiation in addition to heat convection. This is particularly useful in high temperature environments because above 500°C thermal radiation dominates heat transfer. This radiation blocking property is due to the carbon species intentionally trapped in the fibers during the manufacturing process. These dark spots absorb heat radiation and therefore prevent it from passing through the material.

heat

The researchers conducted several tests on their material. In one, he wrapped jet engine fuel tubes in various insulation before heating them with a butane torch for five minutes. The tube insulated with commercial polyimide foam insulation reached 267°C, reaching 159°C protected by a conventional fibrous silica airgel, while the new ceramic airgel kept the temperature below 33°C.

Shenqiang Ren from the University at Buffalo in the US, who was not involved in this research, describes the work in the field of ceramic aerogels for use in extremely hot conditions as a “significant contribution”. “The manufacturing process is [also] Relatively simple and potentially scalable,” says Ren, adding that the design “could inspire the development of the next generation of extreme materials.

Adapted by Nine Notman, written by Tim Wogan. Resources by Neil Golby.

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Download this one-slide summary with articles and questions to use with your 14-16 year old students when teaching blended materials: rsc.li/3SunSvk