High Toughness Combined with High Strength in Oxide Ceramic Nanofibers

Abstract

Traditional oxide ceramics are inherently brittle and highly sensitive to defects, making them vulnerable to failure under external stress. As such, endowing these materials with high strength and high toughness simultaneously is crucial to improve their performance in most safety‐critical applications. Fibrillation of the ceramic materials and further refinement of the fiber diameter, as realized by electrospinning, are expected to achieve the transformation from brittleness to flexibility owing to the structural uniqueness. Currently, the synthesis of electrospun oxide ceramic nanofibers must rely on an organic polymer template to regulate the spinnability of the inorganic sol, whose thermal decomposition during ceramization will inevitably lead to pore defects, and seriously weaken the mechanical properties of the final nanofibers. Here, a self‐templated electrospinning strategy is proposed for the formation of oxide ceramic nanofibers without adding any organic polymer template. An example is given to show that individual silica nanofibers have an ideally homogeneous, dense, and defect‐free structure, with tensile strength as high as 1.41 GPa and toughness up to 34.29 MJ m−3, both of which are far superior to the counterparts prepared by polymer‐templated electrospinning. This work provides a new strategy to develop oxide ceramic materials that are strong and tough.

A flexible precontact CNT-Al2O3 fiber sensor resistant to extreme temperatures

“…In all the nanoscale structures of ceramic materials, the one-dimensional structure with a large aspect ratio, with the advantages of high surface area, low density, excellent mechanical properties and multifunctionality, is one of the main structures of ceramic materials with flexibility. Among the various preparation processes, electrospinning, 17–19 blow spinning, 16,20 chemical vapor deposition (CVD) 21,22 and atomic layer deposition (ALD) 23,24 are suitable options to accomplish this task. For example, a large-area flexible TiO 2 nanofiber network is prepared by the extended electrospinning method, and the flexible pressure sensor based on the ceramic network can withstand high temperatures up to 370 °C.…”

“…Among the various preparation processes, electrospinning, [17][18][19] blow spinning, 16,20 chemical vapor deposition (CVD) 21,22 and atomic layer deposition (ALD) 23,24 are suitable options to accomplish this task. For example, a large-area flexible TiO 2 nanofiber network is prepared by the extended electrospinning method, and the flexible pressure sensor based on the ceramic network can withstand high temperatures up to 370 °C.…”

Hydrogen-Bonded Mesoporous Frameworks with Tunable Pore Sizes and Architectures from Nanocluster Assembly Units

“…In recent years, besides the molecular-level assembly, in order to expand the “family” members of the appealing porous materials, construction of hierarchical mesoporous frameworks via the modular self-assembly of subnanoscale-level, even nanoscale-level, building units, e.g., the polyoxometalate (POM) clusters, has turned a hot topic. − These nanoscale clusters with several dozens of atoms inherently own some unique properties, such as small size effects, surface quantum effects, and so forth. − If such nanosized clusters could be further assembled or arranged into a multilevel ordered mesoporous framework via a regular pattern, some new superior properties might be endowed. − Besides, for these mesoporous nanocluster frameworks, the spatially circular distribution of cluster building units on the inner walls of spherical mesopores may alter their surface surroundings and charge distributions of clusters, resulting in boosted reaction dynamics. − Similar to the prominent porous materials of metal–organic frameworks (MOFs), , covalent–organic frameworks (COFs), , and hydrogen-bonded organic frameworks (HOFs), − such multilevel mesoporous nanocluster frameworks are of great potential in future applications.…”

Electrospinning Nonspinnable Sols to Ceramic Fibers and Springs

“…Also, a good solvent is required to dissolve a certain amount of polymer to allow sufficient polymer chain entanglement. , Yet, the ceramic precursors dispersed in such polymer/solvent medium tend to segregate into various phases due to their varied solubility, resulting in porous structures and unevenly distributed crystalline and amorphous phases. − Possible phase separations in the solution also makes creating homogeneous multicomponent and high entropy ceramic fibers very challenging. − Moreover, in the precursor fibers, the polymer intermixes with the sol–gel species and occupies a significant volume of the materials (typically about 40–60 wt %), removing the polymer leaves inorganic fibers with rough surfaces and pores. These structural defects severely deteriorate the mechanical properties of calcined ceramic fibers, , limiting their installation in applications such as filtration, biomedical engineering, sensing, automobiles, energy generation, storage, etc . − …”

“…Choi et al and Lee et al produced SiO 2 and TiO 2 /SiO 2 fibers from aged alkoxide solutions, , but the generated fibers have highly nonuniform diameters and beaded morphology due to the Rayleigh and electric field-induced axisymmetric instabilities. , Huang et al improved the spinnability of the SiO 2 /TiO 2 solution by systematically evaluating the solution properties as functions of precursor composition, water content, and pH values, yet the obtained microfibers display unsatisfactory structural homogeneity . Recently, Ding’s group proposed a vacuum concentration process to remove the solvents partially and facilitate the precursors condensing into molecular chains and generating solutions with viscosities between 100 and 400 mPa s. ,, This approach has enabled a series of ceramic fiber products with superior properties, although fundamentally, it still relies on tuning the rheological properties to create spinnable systems.…”