Researchers have made ultralight, highly porous, compressible, and heat-resistant sponge-like materials from nanoscale ceramic fibers. The highly deformable material is made by tangling ceramic nanofibers into a sponge. The method used is inexpensive and scalable for making large quantities.
Since ceramics are brittle materials, cracks tend to propagate quickly, leading to catastrophic failure with even the slightest deformation. While that’s true for all traditional ceramics, things are different at the nanoscale, where cracks and flaws become so small that it takes much more energy to activate them and cause them to propagate. Nanoscale fibers also promote deformation mechanisms such as “creep,” in which atoms can diffuse along grain boundaries, enabling the material to deform without breaking.
Because of these nanoscale dynamics, materials made from ceramic nanofibers have the potential to be deformable and flexible, while maintaining the heat resistance that makes ceramics useful in high-temperature applications. The problem is that such materials are not easy to manufacture. One often-used method of making nanofibers, called electrospinning, doesn’t work well with ceramics. Another potential option, 3D laser printing, is expensive and time-consuming.
The method to make this material is solution blow-spinning that uses air pressure to drive a liquid solution containing ceramic material through a tiny syringe aperture. As the liquid emerges, it quickly solidifies into nanoscale fibers that are collected in a spinning cage. The collected material is then heated, which burns away the solvent material, leaving a mass of tangled ceramic nanofibers that looks a bit like a cotton ball.
The method was used to create sponges made from a variety of different types of ceramics, and showed that the materials had some remarkable properties. The sponges were able to rebound after compressive strain up to 50 percent, something that no standard ceramic material can achieve. The sponges can maintain that resilience at temperatures up to 800 °C.
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 a 7-millimeter-thick sponge made from titanium dioxide (a common ceramic material) nanofibers. After heating the bottom of the sponge to 400 °C 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 de-formability make them potentially useful as an insulating material where flexibility is important; for example, as an insulating layer in firefighters’ clothing. Another potential use could be water purification. Titanium dioxide is a well-known photo-catalyst used to break down organic molecules, killing 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.