February 18, 2019 6:43:03 pm
Scientists have created a light, durable ceramic aerogel that can withstand intense heat and severe temperature, and could be used for insulating future spacecraft.
Ceramic aerogels have been used to insulate industrial equipment since the 1990s, and they have been used to insulate scientific equipment on NASA’s Mars rover missions.
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However, the new version, developed by researchers at the University of California, Los Angeles (UCLA) in the US, is much more durable after exposure to extreme heat and repeated temperature spikes, and much lighter.
Its unique atomic composition and microscopic structure also make it unusually elastic, according to the study published in the journal Science.
When it is heated, the material contracts rather than expanding like other ceramics do, researchers said.
It also contracts perpendicularly to the direction that it is compressed — imagine pressing a tennis ball on a table and having the centre of the ball move inward rather than expanding out — the opposite of how most materials react when compressed.
As a result, the material is far more flexible and less brittle than current state-of-the-art ceramic aerogels.
It can be compressed to five per cent of its original volume and fully recover, while other existing aerogels can be compressed to only about 20 per cent and then fully recover.
Despite the fact that more than 99 per cent of their volume is air, aerogels are solid and structurally very strong for their weight. They can be made from many types of materials, including ceramics, carbon or metal oxides.
Compared with other insulators, ceramic-based aerogels are superior in blocking extreme temperatures, and they have ultralow density and are highly resistant to fire and corrosion — all qualities that lend themselves well to reusable spacecraft.
However, current ceramic aerogels are highly brittle and tend to fracture after repeated exposure to extreme heat and dramatic temperature swings, both of which are common in space travel.
The new material is made of thin layers of boron nitride, a ceramic, with atoms that are connected in hexagon patterns, like chicken wire.
In the research, the material withstood conditions that would typically fracture other aerogels.
It stood up to hundreds of exposures to sudden and extreme temperature spikes when the engineers raised and lowered the temperature in a testing container between minus 198 degrees Celsius and 900 degrees above zero over just a few seconds.
In another test, it lost less than one per cent of its mechanical strength after being stored for one week at 1,400 degrees Celsius.
“The key to the durability of our new ceramic aerogel is its unique architecture. Its innate flexibility helps it take the pounding from extreme heat and temperature shocks that would cause other ceramic aerogels to fail,” Xiangfeng Duan, a UCLA professor who led the study.
Ordinary ceramic materials usually expand when heated and contract when they are cooled. Over time, those repeated temperature changes can lead those materials to fracture and ultimately fail.
The new aerogel was designed to be more durable by doing just the opposite — it contracts rather than expanding when heated.
Duan said the process researchers developed to make the new aerogel also could be adapted to make other ultra-lightweight materials.
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