video: Mechanical compression test of ceramic aerogels. view more
Credit: X. Xu and X. Duan
Researchers have developed a near weightless material, comprised mostly of air, capable of both withstanding and protecting against some of the most extreme temperatures experienced in aerospace and industrial environments. It performed well when heated to 900 °Celsius (C) and then rapidly cooled to -198 °C, the authors say. Their new ceramic aerogel is engineered with unusual double-negative-index properties and demonstrates exceptional structural stability and superinsulation, making it an ideal material to be used in demanding applications like the heat shields on space vehicles. Aerogels are a composite material made mostly of air encompassed within a network of a solid medium, such as ceramic, metal, or carbon. Ceramic aerogels are incredibly lightweight and possess traits highly desired for enduring demanding environments. However, most conventional ceramic aerogels are brittle and susceptible to degradation due to extended high-temperature exposure or large and rapid temperature swings. According to the authors, these issues have greatly limited the use of ceramic aerogels as a super-insulating material. Xiang Xu and colleagues report on the design of a unique ceramic aerogel created using atomically thin sheets of hexagonal boron nitride (h-BN). By carefully engineering the ceramic aerogel microstructure, Xu et al. were able to achieve both a negative Poisson's ratio (a measure of a material's tendency to bulge outward when compressed) as well as a negative thermal expansion coefficient. To assess the material's mechanical and thermal capabilities, the authors ran a series of tests, including heating the aerogel to 900 °C and then rapidly cooling it -198 °C repeatedly, and at a rate of 275 °C per second. Xu et al. also evaluated the effect of long-term temperature stress by exposing the material to temperatures approaching 1500 °C in a vacuum. According to the results, the aerogel remained largely unchanged with near-zero strength loss following the rigorous trials. Manish Chhowalla and Deep Jariwala discuss the potential of the aerogel in a related Perspective.
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Journal
Science