It consists of more than 99 percent of air and withstands extreme temperature jumps: Researchers have developed a so-called airgel, which survives rapid temperature changes between minus 198 degrees and plus 900 degrees Celsius without damage.
The extraordinary material isolates extremely well and may be suitable for use in space, reports the group around Xiangfeng Duan from the University of California in Los Angeles in the journal "Science". Because in near-Earth orbit several hundred degrees can lie between the sun-facing and the sun-remote side of a probe. A rotation therefore means an enormous and very rapid temperature change.
Ultra-light fabrics
Aerogels are so porous that they consist of more than 99 percent of air or free space. That makes them extremely light and elastic. The ultra-light fabrics were discovered in the early thirties, but then fell into oblivion until the seventies. However, due to the promising properties of sponge-like materials, airgel research has been experiencing a boom for several years.
So far, aerogels have often not withstood large thermal gradients or persistently high temperatures, the researchers explain. They therefore wanted to develop a more resilient material.
The basis of their super insulator is boron nitride, a boron-nitrogen compound that can form honeycomb structures. These already very stable, flat structures bound the scientists in a three-dimensional, net-like structure. This makes it very easy to plastically deform.
Duan and colleagues attribute that their material is so well insulated to three main factors: Firstly, the very low density of the material reduces the heat conduction in the solid. Although a hot body emits heat radiation, this is less effective than heat conduction. Second, in the boron nitride structure, fractions exist in the range of nanometers (millionths of a millimeter). These hinder the heat conduction. Third, the pore walls are designed as double walls and thus isolate similar to double-glazed windows.
Oszie Tarula / UCLA
Samples of the airgel
In order to test the effect of thermal shocks on the material, the researchers developed a special tube: one end was placed in one oven, the other was cooled to minus 198 degrees Celsius with liquid nitrogen. Air blasts sent a sample back and forth between the two ends. This resulted in temperature changes of about 275 degrees - per second and still no problem for the new airgel.
In 20 years after Proxima Centauri
The material developed offers two additional benefits, praising researchers from the University of Cambridge, Manish Chhowalla, and University of Pennsylvania's Deep Jariwala, who were not involved in the study. The material does not expand with greater heat, but pulls something together. On the other hand, it has a negative so-called Poisson number: that is, it is pulled laterally, it is not flatter, but expands up and down.
The researchers can imagine that the material could be suitable for a laser sail. Here, a very light material is to be brought by laser beams to about 20 percent of the speed of light. In this way, a probe could reach the nearest-Earth star, the 4.2 light-years distant Proxima Centauri, in just over 20 years.