Novel ceramic nanofibre sponges

A CERAMIC nanofibre material that is not only heat-resistant but also highly deformable has been manufactured using an inexpensive and scalable method.

Nothing beats a sip of piping hot tea from your favourite mug. But then it slips from your grasp – and you see the very instant it hits the ground. On impact, what looks at first like an innocent hairline crack suddenly shoots through the mug like a lightning bolt, shattering it almost instantaneously.

Despite their fragility and rigidity, the heat-resistant properties of ceramics mean we use them for a wide range of day-to-day and industrial applications. Now, a team of US and Chinese researchers have used nanofibres to help overcome the material’s limitations.

Brown University’s Huajian Gao said: “At the nanoscale, cracks and flaws become so small that it takes much more energy to activate them and cause them to propagate. Nanoscale fibres also promote deformation mechanisms such as what is known as creep, where atoms can diffuse along grain boundaries, enabling the material to deform without breaking.'

This allows nanofibre ceramic materials to be deformable and flexible, whilst maintaining the heat resistance that makes them useful in high-temperature applications. However, traditional methods of creating nanofibres such as electrospinning are difficult to apply to ceramics, while 3D laser printing is expensive and time-consuming.

The international team have published details of their new technique, solution blow-spinning, in Science Advances. It uses air pressure to drive a liquid solution containing ceramic material through a tiny syringe aperture, which quickly solidifies into nanoscale fibres. The material is collected in a spinning cage and then heated, burning away the solvent to leave a mass of tangled nanofibres resembling a cotton ball.

Gao said: 'This paper demonstrates that we can make a material that's highly deformable but resistant to high temperature by tangling ceramic nanofibres into a sponge, and the method we use for doing it is inexpensive and scalable to make these in large quantities.'

Sponges were created from a variety of different types of ceramics, and demonstrated some interesting properties. For example, they rebounded after compressive strain up to 50% under temperatures reaching 800°C. The capacity for thermal insulation was also demonstrated by placing a flower petal on a 7mm-thick sponge made from the ceramic titanium dioxide (TiO2), which did not wilt after heating at 400°C for 10 minutes.

Potential applications include use in water purification. TiO2 is a well-known photocatalyst used to break down organic molecules, which kills bacteria and other microorganisms in water. A TiO2 sponge was demonstrated to absorb 50 times its weight in water containing an organic dye, then degrade the dye under illumination within 15 minutes. The sponge could then be reused, which is not currently possible with the TiO2 powders normally used in water purification.

Another author of the paper, Hui Wu from Tsinghua University, said: 'The process we used for making these is extremely versatile; it can be used with a great variety of different types of ceramic starting materials, so we think there's huge prospect for potential applications.'

Science Advances: http://advances.sciencemag.org/content/3/6/e1603170