Composite fiber can protect firefighters from extreme heat

Firefighter clothing, spacecraft insulation, and coatings for deep-buried detectors could all benefit from a novel thermal-insulating material developed by scientists in China and the US. The team has demonstrated that its ceramic aerogel exhibits superior thermal insulation over materials currently used for these applications.

Ceramic aerogels are ultra-porous materials, consisting of thin layers of ceramic that separate small air pockets. A typical ceramic airgel is 99% air. Ceramic barriers hinder heat transfer by convection between air bubbles, meaning these materials can serve as heat insulators. There is a problem though – ceramics are usually brittle, which can lead to catastrophic failure when the material is placed under stress.

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

Two firefighters dealing with a fire in an aircraft with a water hose and an FIR engine in the background

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 candyfloss-like ceramic felt. Then, he mechanically folded this felt in a zigzag pattern. 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 not allowing the fibers within the material to glide past each other when tensioned, as one might expect. Instead, the fibers are bent under tension, with the expansion of the fibers running in one direction being counteracted by the contraction of fibers running in the other direction. This design means that the structure is highly mechanically stable.

Another aspect of the material’s design means it can block thermal radiation in addition to thermal convection. This is particularly useful in high temperature environments, as 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 thermal radiation and therefore block it from traveling through the material.

heat up

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

Shenqiang Ren of 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,’ Ren says, 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 students when teaching mixed material: rsc.li/3SunSvk

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