由陶瓷納米纖維制成的海綿狀材料除了保留陶瓷特性外，還使其具備了高度變形的能力，就像海綿一樣。這種多孔結構的海綿陶瓷可以作為水凈化裝置，也可以用作絕緣保護材料。這項開發是布朗大學的Huajian Gao與清華大學的Hui Wu和Xiaoyan Li合作完成，并在Science Advances（科學進展）期刊發表。

海綿陶瓷在耐高溫的同時也可以像海綿那樣高度變形

材料的物理特性在納米級別會發生巨大變化，對于陶瓷材料來說脆性和斷裂缺陷也會變小，納米陶瓷纖維改善了材料的蠕變性，促進陶瓷達成類似海綿的變形機制。

但陶瓷纖維是很難制備的，傳統的纖維制造方法肯定行不通，3D打印則不僅耗時并且昂貴。

因此，研究人員使用了一種稱為“blow-spinning”（吹紡）的方法，該方法是由Wu在清華實驗室開發的。該方法是通過微型注射器來驅動含陶瓷材料的液體溶液，將這些很快凝固的材料收集并加熱，剩下的就是像棉花球一樣的陶瓷纖維。

氧化鋯

“海綿陶瓷”在攝氏800度仍然保持韌性外，研究人員還通過一組對比試驗，讓人們充分感受這種“海綿陶瓷”優異的隔熱效果。

氧化鋯材質的海綿陶瓷具備優異的隔熱效果

如圖所示，花瓣放在7毫米厚度的不同材質下進行底部為400攝氏度的加溫。10分鐘后，氧化鋯材質海綿陶瓷上方的花瓣由于脫水變得松脆，其他進行對比的材質則全都燒焦枯萎。具備這樣的耐熱性和變形性，則說明它可以用作消防員專用消防服。

二氧化鈦

除此之外，還可以利用二氧化鈦的光催化作用，這種材質的海綿陶瓷不僅可以殺死水中的微生物和細菌，降解水中的有機染料，還可以像海綿一樣循環利用。二氧化鈦海綿吸水量為其自身重量的50倍，光照條件下，15分鐘即可完成對染料的降解，完成凈化后將水擠出就可以再次吸水凈化。

研究人員稱，通過這種制作工藝，可以制備不同材質的“海綿陶瓷”，而這種材料應該會有很廣闊的應用前景。

粉體圈 譯

注：

由于小編文字水平和翻譯功底有限，以上內容或許存在錯漏之處，有興趣的讀者可自行閱讀原文。

New ceramic nanofiber 'sponges' could be used for flexible insulation, water purification

Researchers have found a way to make ultralight sponge-like materials from nanoscale ceramic fibers. The highly porous, compressible and heat-resistant sponges could have numerous uses, from water purification devices to flexible insulating materials.

"The basic science question we tried to answer is how can we make a material that's highly deformable but resistant to high temperature," said Huajian Gao, a professor in Brown University's School of Engineering and a corresponding author of the research. "This paper demonstrates that we can do that by tangling ceramic nanofibers into a sponge, and the method we use for doing it is inexpensive and scalable to make these in large quantities."

The work, a collaboration between Gao's lab at Brown and the labs of Hui Wu and Xiaoyan Li at Tsinghua University in China, is described in the journal Science Advances.

As anyone who has ever dropped a flower vase knows well, ceramics are brittle materials. Cracks in ceramics 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.

"At the nanoscale, cracks and flaws become so small that it takes much more energy to activate them and cause them to propagate," Gao said. "Nanoscale fibers 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."

Because of those nanoscale dynamics, materials made from ceramic nanofibers have the potential to be deformable and flexible, while maintaining the heat resistance that make ceramics useful in high-temperature applications. The problem is that such materials aren't easy to make. One often-used method of making nanofibers, known as electrospinning, doesn't work well with ceramics. Another potential option, 3-D laser printing, is expensive and time-consuming.

So the researchers used a method called solution blow-spinning, which had been developed previously by Wu in his lab at Tsinghua. The process 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 researchers used the method to create sponges made from a variety of different types of ceramics and showed that the materials had some remarkable properties.

For example, the sponges were able to rebound after compressive strain up to 50 percent, something that no standard ceramic material can do. And the sponges can maintain that resilience at temperatures up to 800 degrees Celsius.

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) nanofibers. After heating the bottom of the sponge to 400 degrees Celsius 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. For example, Gao says, the material could be used as an insulating layer in firefighters' clothing.

Another potential use could be in water purification. Titanium dioxide is a well-known 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.

"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," said Wu, one of the corresponding authors from Tsinghua. "So we think there's huge prospect for potential applications."