Ultra-light sponge material made from ceramic nanofibres
Ceramic is a very heat resistant and strong material. However, if you have ever dropped a plate or mug, you also know that the material is very brittle. Now, researchers at Brown University and Tsinghua University have developed a super lightweight material made from ceramic nanofibres that can be squished like a sponge.
The aim of the project was to create a material that was deformable, but also heat resistant. While ceramics are usually brittle and crack easily, at nanoscale, things work differently. At that level, cracks and flaws becomes so small that it takes much more energy to activate them and cause them to propagate. Nanoscale fibres promote deformation mechanisms in which atoms can diffuse along grain boundaries, which enables the material to deform without breaking.
Thanks to these properties, materials made from ceramic nanofibres have the potential to be deformable and flexible while maintaining the heat resistance. Common methods to make nanofibres, such as electrospinning, don’t work well with ceramics, while 3D printing is expensive and takes a long time.
Therefore, the researchers had to use a different method, called blow-spinning. The process uses air pressure to push a liquid solution containing ceramic material through a tiny syringe aperture. When the liquid emerges, it solidifies into nanoscale fibres that are collected in a spinning cage, similar to a cotton candy machine. The collected material is then heated, burning away the solvent material and leaving a mass of tangled ceramic nanofibres.
This sponge-like material is able to rebound after compressive strain up to 50 per cent, something that no standard ceramic material can do. In addition, the material can maintain that resilience at temperatures up to 800 degrees Celsius (1472 degrees Fahrenheit).
The research also showed that the sponges had a remarkable capacity for high-temperature insulation. In one experiment, the researchers placed a flower petal on top of 7-millimeter-thick sponge made from titanium dioxide (a common ceramic material) nanofibres. After heating the bottom of the sponge to 400 degrees Celsius (752 degrees Fahrenheit) for 10 minutes, the flower on top barely wilted. Meanwhile, petals placed on other types of porous ceramic materials under the same conditions were burnt to a crisp.
The sponges’ heat resistance and its deformability make them potentially useful as an insulating material where flexibility is important. It could be used, for example, as an insulating layer in fire fighters’ clothing.
Another potential use could be in water purification. Titanium dioxide is a photocatalyst used to break down organic molecules, which kills bacteria and other microorganisms in water. The researchers showed that a titanium dioxide sponge could absorb 50 times its weight in water containing an organic dye. Within 15 minutes, the sponge was able to degrade the dye under illumination. With the water wrung out, the sponge could then be reused, something that can’t be done with the titanium dioxide powders normally used in water purification.
In addition to these, there may be other applications for ceramic sponges that the researchers haven’t yet considered, so there is a good chance we’ll here more about this material in the future.
Photos: Gao/Li/Wu/Brown University/Tsingua University / Alan Levine