Large-Scale Roll-to-Roll Manufacturing of Flexible, Hydrophobic, and Fire-Resistant Mica/SiO2 Nanofiber Aerogel Paper.

The light weight and low thermal conductivity of ceramic aerogels make them attractive as heat barriers in harsh environments like those needed on spacecraft. But while aerogels made from nanoparticles can be good thermal insulators, they tend to be brittle, limiting their applications. Aerogels made from nanofibers are more flexible but struggle to perform as practical thermal insulators. Now, a team led by Yang Si and Bin Ding of Donghua University have made a ceramic aerogel from both SiO2 nanofibers and nanoparticles. To make the new aerogel, the team starts with a SiO2 nanoparticle aerogel, grinds it up, and then mixes it with the nanofibers to form a hierarchical, cellular structure that is both flexible and resistant to heat and cold (ACS Appl. Mater. Interfaces 2019, DOI: 10.1021/acsami.9b10018). The researchers showed that a material consisting of 30% nanoparticle aerogel pieces by weight can withstand a butane blowtorch and a liquid-nitrogen

Ceramic aerogels have great potential in the areas of thermal insulation, catalysis, filtration, environmental remediation, energy storage, etc. However, the conventional shaping and post-processing of ceramic aerogels are plagued by their brittleness due to the inefficient neck connection of oxide ceramic nanoparticles. Here a versatile thermal-solidifying direct-ink-writing has been proposed for fabricating heat-resistant ceramic aerogels. The versatility lies in the good compatibility and designability of ceramic inks, which makes it possible to print silica aerogels, alumina-silica aerogels, and titania-silica aerogels. 3D-printed ceramic aerogels show excellent high-temperature stability up to 1000 °C in air (linear shrinkage less than 5%) when compared to conventional silica aerogels. This improved heat resistance is attributed to the existence of a refractory fumed silica phase, which restrains the microstructure destruction of ceramic aerogels in high-temperature environments. Benefiting from low density (0.21 g cm-3 ), high surface area (284 m2 g-1 ), and well-distributed mesopores, 3D-printed ceramic aerogels possess a low thermal conductivity (30.87 mW m-1 K-1 ) and are considered as ideal thermal insulators. The combination of ceramic aerogels with 3D printing technology would open up new opportunities to tailor the geometry of porous materials for specific applications.

A review on the emerging resilient and multifunctional ceramic aerogels

Thermal insulation under extreme conditions requires materials that can withstand complex thermomechanical stress and retain excellent thermal insulation properties at temperatures exceeding 1,000 degrees Celsius1–3. Ceramic aerogels are attractive thermal insulating materials; however, at very high temperatures, they often show considerably increased thermal conductivity and limited thermomechanical stability that can lead to catastrophic failure4–6. Here we report a multiscale design of hypocrystalline zircon nanofibrous aerogels with a zig-zag architecture that leads to exceptional thermomechanical stability and ultralow thermal conductivity at high temperatures. The aerogels show a near-zero Poisson’s ratio (3.3 × 10−4) and a near-zero thermal expansion coefficient (1.2 × 10−7 per degree Celsius), which ensures excellent structural flexibility and thermomechanical properties. They show high thermal stability with ultralow strength degradation (less than 1 per cent) after sharp thermal shocks, and a high working temperature (up to 1,300 degrees Celsius). By deliberately entrapping residue carbon species in the constituent hypocrystalline zircon fibres, we substantially reduce the thermal radiation heat transfer and achieve one of the lowest high-temperature thermal conductivities among ceramic aerogels so far—104 milliwatts per metre per kelvin at 1,000 degrees Celsius. The combined thermomechanical and thermal insulating properties offer an attractive material system for robust thermal insulation under extreme conditions.

Lightweight, thermally insulating SiBCN/Al2O3 ceramic aerogel with enhanced high-temperature resistance and electromagnetic wave absorption performance

Ceramic aerogels have exhibited many superior characteristics with promising applications. As an attractive material system for thermal insulation under extreme conditions, ceramic aerogels are required to withstand complex thermomechanical stress to retain their super-insulating properties but, they often suffer from severe fracture damage that can lead to catastrophic failure. Herein, inspired by the tendrils of Parthenocissus, we report a design and synthesis of ultra-stretchable ceramic aerogels constructed by highly buckled nanofibers. The buckling of nanofibers is formed by asymmetric deformation through two-component off-axial electrospinning method. The resulting aerogels feature an ultra-large stretchability with a tensile strain of up to 150% and high restorability with a tensile strain of up to 80%. They also display a near-zero Poisson's ratio (4.3 × 10-2) and a near-zero thermal expansion coefficient (2.6 × 10-7 per°C), resulting in excellent thermomechanical stability. Benefiting from this ultra-stretchability, the aerogels exhibit a unique tensile-insensitive thermal insulation performance with thermal conductivities remaining only ≈106.7 mW m-1 K-1 at 1000°C. This work promotes the development of ceramic aerogels for robust thermal insulation under extreme conditions and establishes a set of fundamental considerations in structural design of stretchable aerogels for a wide spectrum of applications.

Ceramic aerogels are acclaimed as ideal materials for extreme environments due to their ultrahigh porosity, low density, and exceptional thermal stability. However, the practical application of traditional ceramic aerogels is constrained by their inherent mechanical brittleness. Herein, a strategy is proposed to customize mechanically tunable aerogels by armoring ceramic nanounits with pyrolytic carbon (PyC). The PyC encapsulating layers with various thicknesses are transformed into ductile tights or rigid armors, facilitating the mechanical customization of BN@PyC aerogel from superelasticity to rigidity across scales. Interestingly, the PyC armor imparts unique versatility to the aerogel, including flame retardancy, elastic response conductivity, and thermal conductivity. Furthermore, owing to the thermal stability of the PyC armor, the BN@PyC aerogel maintains its mechanical integrity even after high‐temperature thermal treatment, and exhibits an unexpected resistance to butane torch ablation. Integrating mechanical stability, high‐temperature resistance, and multifunctionality, BN@PyC aerogels offer new possibilities for scalable applications in extreme environments. This facile strategy of armoring brittle ceramic aerogels with PyC provides a novel reference for customizing the mechanical properties of multifunctional aerogels.

Ceramic aerogels are promising high-temperature thermal insulation materials due to their outstanding thermal stability and oxidation resistance. However, restricted by nanoparticle-assembled network structures, conventional ceramic aerogels commonly suffer from inherent brittleness, volume shrinkage, and structural collapse at high temperatures. Here, to overcome such obstacles, 3D ultralight and highly porous carbon tube foams (CTFs) were designed and synthesized as the carbonaceous precursors, where melamine foams were used as the sacrificial templates to form the hollow and thin-wall network structures in the CTFs (density: ∼4.8 mg cm-3). Then, the arbitrary-shaped silicon carbide (SiC) nanofibrous aerogels (SNFAs) were obtained through a simple chemical vapor deposition (CVD) process on the CTFs. The resulting SNFAs exhibited excellent comprehensive performances: ultralow density (4.2 mg cm-3) and thermal conductivity (21.3 mW m-1 K-1 at room temperature), excellent rigidity (specific modulus: 13.2 kN·m kg-1), and resilient compressibility. The SNFAs could support over 2100 times their weight without visible deformation. Furthermore, the SNFAs also showed exceptional high-temperature thermal stability, which means that they could withstand 1100 °C in an air atmosphere and 1550 °C in an inert atmosphere. These superior comprehensive performances enable SNFAs to be suitable for thermal insulation in harsh environments.

Resilient ceramic aerogels exhibit great potential for applications in harsh environments owing to their unique combination of ultrahigh porosity, lightweight, reversible compressibility, and good thermal and chemical stabilities. However, their applications are severely restricted by the limited size and low yield due to their complicated and time-consuming synthetic procedures. Herein, we developed an efficient method for large-scale production of resilient SiC nanowire aerogels (SiC NWAGs) with tunable densities and desired shapes. The as-synthesized SiC NWAGs displayed excellent high-temperature stability (the maximum working temperature in Ar and air can reach to 1400 and 1000 °C, respectively), outstanding flame-erosion resistance and low thermal conductivity (25 mW m-1 K-1). The easy fabrication of such ceramic aerogel on a large scale will pave the way for the widespread applications of ceramic aerogels.

True three-dimensional (3D) micro-and nanofabrication with two-photon polymerization (2PP) of inorganic-organic hybrid polymer (ORMOCER) synthesized by a modified sol-gel method will be presented. The ultra violet (UV) sensitive ORMOCER designed for integrated optics applications provides exceptional thermal and chemical stability, is transparent in the infrared region, and exhibits low losses at the telecommunication wavelengths. By applying tightly focused infrared femtosecond laser pulses a chemical reaction localized in the vicinity of the focal volume is triggered. Polymerization occurs along the trace of the focus moved in three dimensions, enabling true 3D fabrication. After processing, the non-irradiated resin is removed by appropriate alcohol solution, leaving the polymerized structure. Non-linear character of the interaction along with the well-defined polymerization threshold allows one to overcome the diffraction limit for resolution. This technique is suitable for rapid prototyping of any desired structures, with resolution as high as 100nm. Due to its flexibility 2PP is a very promising technique for the fabrication of micro-optical devices and photonic crystals, in particular those with introduced defects. Recent results and applications of 2PP will be presented.True three-dimensional (3D) micro-and nanofabrication with two-photon polymerization (2PP) of inorganic-organic hybrid polymer (ORMOCER) synthesized by a modified sol-gel method will be presented. The ultra violet (UV) sensitive ORMOCER designed for integrated optics applications provides exceptional thermal and chemical stability, is transparent in the infrared region, and exhibits low losses at the telecommunication wavelengths. By applying tightly focused infrared femtosecond laser pulses a chemical reaction localized in the vicinity of the focal volume is triggered. Polymerization occurs along the trace of the focus moved in three dimensions, enabling true 3D fabrication. After processing, the non-irradiated resin is removed by appropriate alcohol solution, leaving the polymerized structure. Non-linear character of the interaction along with the well-defined polymerization threshold allows one to overcome the diffraction limit for resolution. This technique is suitable for rapid prototyping of any des...

Fabrication and microstructure evolution of monolithic bridged polysilsesquioxane-derived SiC ceramic aerogels

Phenolic and carbon aerogels have important applications for thermal insulation and ablative resistance materials in aerospace field. However, their antioxidant ability in long-term high-temperature aerobic environments faces serious challenges. To solve this problem, Zr/Si preceramic polymer hybridized phenolic resin (PR-ZS) aerogels were prepared via a facile sol-gel method. Compared with pure phenolic aerogel, the hybrid aerogels possess similar porous microstructure but larger specific surface area, better thermo-oxidative stability, and higher compressive strength. After carbonization at 1700 °C, the hybrid aerogels can be transformed to carbide ceramic aerogels with ultrafine nanocrystalline ZrC and SiC particles embedded in the carbon matrix. Ceramic aerogels exhibit good thermal insulative and anti-ablative properties in a butane torch simulated high-temperature and aerobic environment. The linear ablation rate is as low as 0.017 mm min-1, and the backside temperature is below 330 °C at a 20 mm in-depth position after 300 s of burning test, when the front temperature is approximately 960 °C. This work provides a facile approach to fabricate hybrid phenolic aerogels and derived ZrC/SiC/C ceramic aerogels, which target on applications for extreme environments in aerospace field.

Elastic ceramic aerogels are exceptionally suitable for thermal insulating applications, but lacking multi‐mechanical synergistic high strength remains a deficiency. Inspired by the robust protective shells of mollusks in nature, which feature distinct hierarchical ordered structures, exhibiting strong and tough mechanical properties, a system construction and structural governing strategy is proposed to allow the nanostructure to assemble strong and flexible ceramic aerogels. Through the design of a hierarchical multi‐arched structure configurated binary‐soldering‐assemble interfacial topology interlocking, concentrated stress is effectively discrete. This biomimetic strategy enables the effective dissipation of mechanical energy, resulting in ceramic aerogels with exemplary compressive resilience, bendability, tensile resistance, and their strength exceeding that of other nanofibrous aerogels by up to tenfold. Additionally, the flexible aerogels also show remarkable thermal resistance from −196 to 1100 °C and superior thermal insulation capabilities (39.72 mW m−1 K−1), making them more suitable for the applications.

With the prevailing energy challenges and the rapid development of aerospace engineering, high-performance thermal insulators with various functions are attracting more and more attention. Ceramic aerogels are promising candidates for thermal insulators to be applied in harsh environments because of their low thermal conductivity and simultaneously excellent thermal and chemical stabilities. In general, the effective properties of this class of materials depend on both their microstructures and the intrinsic properties of their building blocks. Herein, to enrich the family and broaden the application fields of this class of materials, we prepared ultralight α-Si3N4 nanobelt aerogels (NBAs) with tunable densities ranging from 1.8 to 9.6 mg cm-3. The α-Si3N4 NBA realized resilient compressibility (with a recoverable strain of 40-80%), fire resistance (1200 °C butane blow torch), thermal insulation (0.029 W m-1 K-1), and electronic wave transparency (a dielectric constant of 1-1.04 and a dielectric loss of 0.001-0.004) in one material, which makes it a promising candidate for mechanical energy dissipative, fire-resistant, and electronic wave-transparent thermal insulator to be applied in extreme conditions. The successful preparation of such resilient and multifunctional α-Si3N4 NBAs will open up a new world for the development and widespread applications of ceramic aerogels.

Multifunctional SiC aerogel reinforced with nanofibers and nanowires for high-efficiency electromagnetic wave absorption