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Ceramic aerogels are considered as promising thermal insulation materials used in extreme environments. However, the combination of ultralight, high heat tolerance and ultra-low high-temperature thermal conductivity is still a great challenge for both brittle granular aerogels and micron-porous fibrous aerogels. Here, a dual-template strategy is proposed for the simple fabrication of high-performance nanoporous ceramic aerogels (SARAs) by adopting one-dimensional high-crystallinity and high-aspect-ratio Al 2 O 3 nanorods as the basic unit. After delicate design of the composition and pore structures, SARAs exhibit excellent comprehensive properties including ultra-low density (8.12–28.43 mg cm−3), low room temperature thermal conductivity (down to 0.0246 W m−1 K−1) and extremely high temperature resistance (up to 1400 °C). In addition, the unique nanoporous structure lapped by nanorods also confer SARAs superior high-temperatures thermal insulation performance (0.0949 W m−1 K−1 at 1000 °C). The successful preparation of nanorod aerogels with fascinating properties not only provides a new vision on the pore structure regulation of aerogels for thermal insulation, but also offers an opportunity to develop new ultralight functional ceramic aerogels. • A novel dual-template strategy is proposed for the preparation of rigid ultralight ceramic nanorod aerogels. • Si doping technology imparts aerogels ultra-high temperature resistance up to 1400 °C. • Delicate modulation of the pore structure by ice crystals leads to excellent thermal insulation properties. • The relationship between pore structure, thermal insulation and mechanical properties is established. • The nanoporous structure resulting from inter-lapped nanorods leads to ultra-low thermal conductivity at high temperatures. [ABSTRACT FROM AUTHOR]

Emerging fiber aerogels with excellent mechanical properties are considered as promising thermal insulation materials. However, their applications in extreme environments are hindered by unsatisfactory high-temperature thermal insulation properties resulting from severely increased radiative heat transfer. Here, numerical simulations are innovatively employed for structural design of fiber aerogels, demonstrating that adding SiC opacifiers to directionally arranged ZrO2 fiber aerogels (SZFAs) can substantially reduce high-temperature thermal conductivity. As expected, SZFAs obtained by directional freeze-drying technique demonstrate far superior high-temperature thermal insulation performance over existing ZrO2-based fiber aerogels, with a thermal conductivity of only 0.0663 W·m−1·K−1 at 1000 °C. Furthermore, SZFAs also exhibit excellent comprehensive properties, including ultralow density (6.24–37.25 mg·cm−3), superior elasticity (500 compression cycles at 60% strain) and outstanding heat resistance (up to 1200 °C). The birth of SZFAs provides theoretical guidance and simple construction methods for the fabrication of fiber aerogels with excellent high-temperature thermal insulation properties used for extreme conditions. [ABSTRACT FROM AUTHOR]

Increasing pollution from industrial wastewater containing oils or organic solvents poses a serious threat to both the environment and human health. Compared to complex chemical modifications, bionic aerogels with intrinsic hydrophobic properties exhibit better durability and are considered as ideal adsorbents for oil-water separation. However, the construction of biomimetic three-dimensional (3D) structures by simple methods is still a great challenge. Here, we prepared biomimetic superhydrophobic aerogels with lotus leaf-like structures by growing carbon coatings on Al2O3 nanorod-carbon nanotube hybrid backbones. Thanks to its multicomponent synergy and unique structure, this fascinating aerogel can be directly obtained through a simple conventional sol-gel and carbonization process. The aerogels exhibit excellent oil-water separation (22 g·g−1), recyclability (over 10 cycles) and dye adsorption properties (186.2 mg·g−1 for methylene blue). In addition, benefiting from the conductive porous structure, the aerogels also demonstrate outstanding electromagnetic interference (EMI) shielding capabilities (~40 dB in X-band). This work presents fresh insights for the preparation of multifunctional biomimetic aerogels. [ABSTRACT FROM AUTHOR]

• A novel fiber-reinforced and opacified (FRO) strategy for aerogel composites. • The composites exhibit ultra-low thermal conductivity (0.031 W·m−1·K−1 at 1100 °C). • The composites show high toughness and remarkable thermal stability up to 1300 °C. • A promising candidate for aircraft thermal protection systems. Fiber-reinforced alumina-silica aerogel composites (FASA), renowned for their high-temperature resistance, low thermal conductivity, and robust mechanical properties, have emerged as a promising candidate for aerospace thermal insulation, especially in harsh environments characterized by intense vibration and oxidation. However, a significant challenge persists in homogeneously doping opacifiers and minimizing thermal conductivity of FASA at elevated temperature, which remains a thorny issue. Herein, we propose a novel fiber-reinforced and opacified (FRO) strategy to fabricate the ZrO 2 fiber-reinforced alumina-silica aerogel composites (ZFASA) that boast ultra-low thermal conductivity (0.031 W·m−1·K−1 at 1100 °C) and excellent mechanical strength (0.44 MPa for compressive strength at 10 % strain and 2.1 MPa for bending strength, maintaining intact even after being rolled by a 1.7 t car). Furthermore, ZFASA exhibits remarkable thermal stability, enduring quartz lamp and butane torch tests at 1300 °C without any obvious change. This work provides a simple yet effective FRO strategy, paving a new path for the preparation of thermal insulating aerogel composites. Consequently, the highly durable and exceptional thermally insulating ZFASA we have developed is poised to better satisfy the demands of the aircraft thermal protection systems in extreme heat environments. [ABSTRACT FROM AUTHOR]

Alumina–silica composite aerogels have drawn vast attention due to their enhanced thermal stability compared to pristine alumina aerogels. However, they are generally weakly-crystallized and tend to experience inevitable sintering and significant surface area loss especially above 1200 °C. In this study, we developed a hydrothermal treatment and supercritical drying strategy for synthesizing novel, well-crystallized, silica-modified boehmite aerogels and fiber-reinforced composites. For the prepared aerogel, network coarsening was significantly hindered and the α -Al 2 O 3 transition was completely prevented even at 1400 °C. As a result, the aerogel exhibits extremely high surface area maintenance (87 % and 53 % after 1300 °C and 1400 °C calcination, respectively) and low linear shrinkage (14 % after 1300 °C calcination) at elevated temperatures. The composite with good toughness shows excellent heat resistance and thermal insulating performance up to 1500 °C. These findings provide a general, direct new idea to improve the thermal tolerance of alumina-based aerogels and extend their applications to higher temperatures. [ABSTRACT FROM AUTHOR]

Alumina aerogels in previous studies which are generally weakly-crystallized tend to experience framework coarsening and corundum formation above 1000 °C. In this work, a straightforward strategy, including hydrothermal treatment and supercritical drying, is developed for tailoring the crystallinity of boehmite colloid and for synthesizing heat resistant, well-crystallized alumina aerogels. Thermal evolution of the aerogel and factors influencing the thermal stability were investigated and discussed in detail. Compared to reported pristine alumina aerogels, the aerogel after calcination at 1300 °C for 2 h shows quite high specific surface area (95 m2/g) and pore volume (0.28 cm3/g), which are 38% and 61% of the corresponding maintenance of the samples at 300 °C, respectively, with α -Al 2 O 3 transition significantly retarded. These findings represent a general rule towards the improvement of heat-resistance of alumina aerogels. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The addition of foreign elements is considered as an effective method to improve the thermal stability of alumina aerogels at a higher temperature. However, the location and stabilizing mechanism of the foreign elements in the alumina aerogel have not been carefully studied. In this work, Si or La was introduced into the network of alumina aerogels through a sol‐gel strategy. The Si‐doped alumina aerogel maintained high surface area (92 m2/g) and pore volume (0.572 cm3/g) even at 1300°C. The dopants prevented α‐Al2O3 transformation at elevated temperatures (1200°C–1300°C). The distribution of foreign ions and their stabilizing mechanism were discussed in detail. The doped alumina aerogels reinforced by mullite fiber felt, with quite low density and thermal conductivity, can be used as high‐temperature thermal insulations. [ABSTRACT FROM AUTHOR]

Materials with high‐performance thermal insulation and excellent flame‐resistance are incredibly desirable for energy conservation and fire safety. In this study, a novel hybrid nanostructure network polybenzoxazine/silica (PBO/SiO2) aerogels were fabricated through facile in situ co‐polymerization sol‐gel methods with ambient pressure drying using benzoxazine (BO) monomers and SiO2 sol as reaction source, N, N‐dimethylformamide (DMF) as the solvent and hydrochloric acid (HCl) as the catalyst. The hybrid nanostructure network was retained by polymerization–induced nanoscale phase separation of PBO and SiO2. The resulting PBO/SiO2 aerogels exhibited finer microstructure, lower density (0.18 g/cm3), thermal conductivity (0.031 W/m·K), and better flame‐resistance in comparison with PBO aerogels. They demonstrated an excellent compressive strength of 0.81 to 1.12 MPa at 10% deformation. The remarkable improvement in thermal insulation and flame‐resistance of PBO/SiO2 aerogels could be attributed to the combined effects of finer microstructure and formation of SiO2 that was "in‐situ" interpenetrated and interacted with silanols (Si‐OH) in the PBO network during the combustion process. The successful synthesis of PBO/SiO2 aerogels highlights the possibility of fabricating a novel high‐performance thermal insulation and excellent flame‐resistance used for energy‐efficient buildings. [ABSTRACT FROM AUTHOR]

In this study, monolithic alumina–silica aerogels with high surface areas and good mechanical properties were synthesized via a facile sol–gel method without solvent exchange. Furthermore, surface areas, microstructures (up to 1300 °C), and mechanical properties of the prepared alumina–silica aerogels were investigated. The sintering and phase transformations of metastable alumina nanoparticles are suppressed owing to the uniformly distributed Si in the alumina–silica aerogels; therefore, the alumina–silica aerogels can maintain much higher specific surface areas after being calcined at 800 °C (575.5 m2/g), 1000 °C (443.2 m2/g), and 1200 °C (120.6 m2/g) compared to pristine alumina aerogels. In addition, the prepared high surface area alumina–silica aerogels show considerably higher strengths than those obtained in previous works. The compressive stress (3 % strain) and elastic modulus of the alumina–silica aerogels reached 1.78 and 65.6 MPa, respectively. The reported alumina–silica aerogels in this study can be good candidates as high-temperature thermal insulators and catalysts. [ABSTRACT FROM AUTHOR]

Silica aerogel is a typical nanoporous material exhibiting excellent thermal insulation property, and its nanostructure change at high temperature has attracted extensive attention. However, there is a lack of real-time research on the nanostructure evolution of silica aerogel under rapid heating. Here, silica aerogel was rapidly heated and imaged via an in-situ heating TEM to characterize the nanostructure evolution of from 600 °C to 1300 °C. After rapid heating at different temperatures, the silica aerogels were characterized by SEM, BET, TG-DSC, XRD and FT-IR. The nanostructure evolution of the aerogels can be divided into three temperature stages and experimental strategies for inhibiting aerogel shrinkage at high temperature can be provided. In stage Ⅰ (600 °C–1000 °C), the shrinkage of the silica aerogels occurred during the initial time of the heating process (within 2 h), and then the structure of silica aerogel became stable. The shrinkage of silica aerogels is primarily caused by the fusion of secondary particles, and increasing the secondary silica aerogel particle size may contribute to reducing the aerogel shrinkage. In stage Ⅱ (1100 °C), the aerogel shrinkage can be observed all the time with the heating process continues, and finally closed to the dense state. The shrinkage of silica aerogels is caused by the fusion of secondary particles and the macropore collapse, increasing the particle size and reducing the macropore content may slow down aerogel shrinkage. In stage Ⅲ (1200 °C–1300 °C), the aerogel will shrink rapidly and reach a dense state in a very short time (within 0.5 h). The shrinkage of silica aerogels is caused by the rapid pore collapse and the rapid fusion and shrinkage of the secondary particles of the aerogel, and pure silica aerogels cannot be used at this temperature. • The SiO 2 aerogels nanostructure evolution under rapid heating condition was studied. • The real time nanostructure changes were observed via an in-situ heating TEM. • Secondary particles fusion and macropore collapse are key factors for the evolution. • The strategies for inhibiting silica aerogel shrinkage at high temperature were provided. [ABSTRACT FROM AUTHOR]

Cellulose diacetate (CDA) based aerogels for thermal insulation were prepared by CDA cross-linked with 2, 4-toluene diisocyanate (TDI) in acetone solvent. The relationship between structure and thermal conductivity of CDA-based aerogels with various reactant ratios (CDA/TDI) was studied. The obtained results show that the increase of reactants causes higher bulk density and smaller porosity of as-prepared aerogels, while its specific surface area decreases with CDA content increasing. Thermal conductivity increases with CDA content increasing, and the minimal value is 0.0313 W m−1 K−1 comparably to that of polyimide aerogel at the same environmental conditions. Meanwhile, the radiant thermal conductivities of CDA-based aerogels were calculated in the range of 0.0021–0.0054 W m−1 K−1 superior to other cellulose aerogels using wafer method. Moreover, the analyses for thermal conductivity distributions of above aerogels suggest that the solid thermal conductivity proportion increases with reactant content increasing, the gaseous one falls down, and the radiant one changes hardly. [ABSTRACT FROM AUTHOR]

Polybenzoxazine (PBO) aerogels were prepared from 4,4′-diamino-diphenylmethane (MDA) benzoxazine monomer by HCl-catalyzed ring-opening polymerization at room temperature after CO2 supercritical drying. This study systematically analyzes the microstructures, thermal insulation properties, compressive properties, and thermal stabilities of the PBO aerogels. The aerogel structure was a cross-linked three-dimensional network with a pore size of 10–140 nm. The conductivity of the aerogels was 0.035–0.057 W/m K under ambient conditions, reducing to 0.009 W/m K at 3 Pa. The compressive strength reached 14.42 MPa under 10% strains, much greater than in SiO2 aerogels of similar density (0.40 g/cm3) reinforced by high-silica glass fiber, which is only 1.30 MPa. Hydrogen bonding interaction was found to be critical for constructing the three-dimensional network structure of the aerogels. This work provides a valuable reference for exploring new structures and expanding the thermal insulation applications of PBO aerogels. [ABSTRACT FROM AUTHOR]

[Display omitted] • The support of multiscale skeleton leads to ultra-low carbonization shrinkage. • Hydrogen bonding induces in situ nano-doping of light-shading carbon layers. • Synergistic multiscale structure results in thermal superinsulation performance. • Heat induced gradient structure shows excellent ablation resistance under 1800 °C. • Al 2 O 3 ceramic skeleton is the structural foundation for these excellent properties. High performance thermal insulation materials are urgently demanded for hypersonic spacecraft. Aerogels are considered as promising candidates owing to their low density and low thermal conductivity. However, some deficiencies, such as the unsatisfactory high-temperature thermal insulation properties and the non-exfoliation-resistant particle porous structure of ceramic aerogels, the ease of oxidation and large carbonization shrinkage of carbon aerogels, remain great challenges for their further applications in high-temperature aerobic ablation environments. Here, we report a multiscale fiber-reinforced Al 2 O 3 -carbon core–shell aerogel composites with low density (0.23–0.31 g·cm−3), excellent mechanical properties (4.89 MPa at 10% strain) and ultra-low carbonization shrinkage (as low as 1.33%). Benefiting from the synergistic effect of in situ nano-doped light-shading carbon layers, porous Al 2 O 3 ceramic rod skeleton and oriented fibers, the composites demonstrate an extremely low high-temperature thermal conductivity (0.055 W·m−1·K−1 at 1200 °C) that is far superior to those of existing high-temperature insulating aerogel composites. In addition, the unique heat-induced gradient structure also confers outstanding thermal protection properties to the composite at 1800 °C with a liner ablation rate of 6.44 μm·s-1and a mass loss rate of 0.167 mg·s−1. This work not only opens a new path for the preparation of thermal superinsulating materials used for spacecraft, but also provides a simple solution to the difficulty of compatibility between low-density insulating porous skeleton and ablation-resistant tough structures, thereby enabling thermal insulation materials to possess desired ablation-resistant properties. [ABSTRACT FROM AUTHOR]

To opacify infrared radiation of mullite fiber-reinforced aerogel composites, SiC coatings were prepared on surfaces of mullite fibers by soaking with polycarbosilane (PCS) solution and then pyrolysis. By impregnating SiC-coated mullite fibers with Al 2 O 3 –SiO 2 sol, then aging and supercritical drying, opacified Al 2 O 3 –SiO 2 aerogel thermal insulation composites were prepared. The influences of the pyrolysis process on effective specific extinction coefficient and phase composition of the SiC-coated mullite fibers were investigated by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction analyses, and their relationship was discussed. The results indicate that the outer-layer coating is composed of β-SiC. When the concentration of the PCS solution was 10 wt%, the effective specific extinction coefficient increased from less than 30.4 to about 56.3 m 2 /kg in the wavelength range of 2.5–7.5 μm. The thermal conductivity of Al 2 O 3 –SiO 2 aerogel composites reinforced by SiC-coated fibers at 1000 °C was 0.049 W/m K, which was lower than that of composites reinforced by blank mullite fibers (0.062 W/m K). [ABSTRACT FROM AUTHOR]

To further reduce the manufacturing cost and improve safety, silica aerogel composites (SAC) with low density and low thermal conductivity synthesized via ambient pressure drying (APD) technology have gradually become one of the most focused research areas. As a solvent, ethanol is flammable and needs to be replaced by other low surface tension solvents, which is dangerous and time-consuming. Therefore, the key steps of solvent replacement and surface modification in the APD process need to be simplified. Here, we demonstrate a facile strategy for preparing high strength mullite fiber reinforced SAC, which is synthesized by APD using water as a solvent, rather than using surface modification or solvent replacement. The effects of the fiber density on the physical properties, mechanical properties, and thermal conductivities of SAC are discussed in detail. The results show that when the fiber density of SAC is 0.24 g/cm3, the thermal conductivity at 1100 °C is 0.127 W/m·K, and the compressive strength at 10% strain is 1.348 MPa. Because of the simple synthesis process and excellent thermal-mechanical performance, the SAC is expected to be used as an efficient and economical insulation material. [ABSTRACT FROM AUTHOR]

Silica aerogels with different particle size were prepared by monodispersed silica sol for the first time. The properties of the silica aerogels under normal and high temperature were systematically studied. Among the four different particle size aerogels, the SA-2 sample consisted of 20.31 ± 1.21 nm particles with narrow size distribution had high temperature resistance and low thermal conductivity. Compared with the traditional acid-base two-step prepared silica aerogels, the monodisperse silica aerogels can significantly increase the temperature resistance while maintaining a low thermal conductivity (0.02723 W·m−1·K−1). The sturdy skeleton structure formed by the interconnection of large particles can effectively inhibit the viscous flow between aerogel particles and avoid pore collapse caused by skeleton failure which can maintain a stable structure until 900 °C and retain a relatively complete structure at 1000 °C with only about 35% volume shrinkage after 2 h heat treatment. At 1100 °C, the viscous flow between aerogel particles and pore collapse cannot be effectively suppressed, and the pure silica aerogels can only be used during a short period at 1100 °C. The results will be meaningful for the design of super thermal insulation materials with high temperature resistance and low thermal conductivity. Unlabelled Image • SiO 2 aerogels with high temperature resistance are prepared by controllable particle size monodispersed silica sol. • Thermal conductivity of SiO 2 aerogels is as low as 0.02723 W·m−1·K−1 despite forming large particle structure. • The aerogel large particle skeleton structure can inhibit the viscous flow between aerogel particles. • Pore collapse caused by skeleton failure can be obviously inhibited depending on formed sturdy skeletons. [ABSTRACT FROM AUTHOR]

Polybenzoxazine (PBO) aerogels with low densities and low thermal conductivities are prepared from Bisphenol A (BPA) benzoxazine monomers by ring‐opened polymerisation using HCl as a catalyser at 10 °C. The obtained PBO aerogels have cross‐linked and 3D network structures with the densities ranging from 0.084 to 0.526 g cm−3. The thermal conductivities under different pressures (3–105 Pa, air) and different atmospheres (N2, Ar, and CO2, 105 Pa) are investigated. The thermal conductivities are in the range of 0.0335–0.0652 W m K−1 under ambient pressure and 0.0098–0.0571 W m K−1 at 3 Pa. The thermal transfer mechanism under different gas pressures is analyzed with increasing pressure. Under different atmospheres, the thermal conductivities decrease as the molecular weight of the gas increases. Compared with the traditional organic foam insulating materials of phenolic foam, polyurethane and polystyrene, which have similar apparent densities, PBO aerogels exhibit lower thermal conductivity of 0.0335 W m K−1 than that of traditional organic foam at room temperature. [ABSTRACT FROM AUTHOR]

To obtain new high-temperature resistant composites that can meet the requirements of aircraft development for thermal insulation and mechanical properties, SiBCO aerogel composites were prepared by sol-gel, supercritical drying and high-temperature pyrolysis with trimethyl borate (TMB) or phenylboronic acid (PBA) as the boron source and mullite fiber as reinforcement. The structure and composition of the SiBCO aerogel and its composites were characterized with SEM, FT-IR, ICP and nitrogen adsorption tests. The specific surface area of the SiBCO aerogel is 293.22 m2/g, and the pore size is concentrated in the range of 10–150 nm. The mechanical properties, the thermal insulation properties and the temperature resistance were also studied. Due to the introduction of boron, the temperature resistance of SiBCO aerogel composites is improved greatly, and the service temperature of composites reached 1773 K. When n (TMB)/n (TEOS) = 1/1, the temperature resistance of the composites is the best. After heating in air at 1773 K for 30 min, the shrinkage of SiBCO aerogel composites is only 2.45%, and the thermal conductivity of the composites is 0.138 W/(m·K) at 1773 K. In addition, the type and amount of catalyst also have certain effects on the mechanical properties and temperature resistance of the composites. [ABSTRACT FROM AUTHOR]

To overcome the brittleness issue of SiCO aerogels, the polyacrylonitrile-based (PAN) carbon fiber was impregnated with SiCO sol to obtain carbon fiber-reinforced SiCO aerogel composites (C/SiCO). SiCO sol was prepared through an acid-alkaline two-step catalysis by using methyltrimethoxysilane (MTMS) and dimethyldiethoxysilane (DMDES) as precursors. C/SiCO-1, C/SiCO-2 and C/SiCO-3 were obtained after repeated impregnation of the SiCO sol and gelating, aging, supercritical drying and pyrolyzing one to three times. SEM images show that the SiCO aerogel fills the pores between the carbon fibers, and the nanoporous structure of the SiCO aerogel can effectively improve the thermal insulation of the composites. As the times of impregnation of the SiCO sol increased, the mechanical properties and oxidation resistance of C/SiCO have been improved significantly. The bending strength of C/SiCO-3 was 32.52 MPa, and the compressive strength (25%ε) was 51.98 MPa. After heating at 1600 °C, the linear shrinkage in the thickness direction of C/SiCO-1 was 20.72%, while that of C/SiCO-3 was only 1.85%. A dense SiO 2 molten oxide film formed on the surface of C/SiCO at high temperature, and its extremely low oxygen permeability effectively protected the inside of the composites. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ultraviolet assisted direct-write printing strategy was proposed for preparing aerogels. • This printing strategy has a considerable feature of solidification-while-printing. • Spatially complex architectures have been printed without auxiliary support. • Multiple crosslinks endow 3D-printed aerogels with excellent mechanical properties. • 3D-printed aerogels have a low thermal conductivity of 37.48 mW·m−1·K−1. Developing aerogels with a tailored geometric feature is of prime importance for enlarging their functional effects in application scenarios. However, conventional manufacturing techniques have remained challenging in the on-demand shaping of aerogels due to their costly and time-consuming fabrication process and poor designability of casting molds. Herein, an ultraviolet-assisted direct-write printing strategy has been proposed for fabricating polyorganosiloxane-based aerogels with tunable molecular triple-crosslinks consisting of hydrogen bonds, hydrocarbon chains, and polysiloxanes. The implementation of direct-write printing depends on the close synergy of consecutive ink deposition and instantaneous photopolymerization, appearing as a considerable characteristic of solidification-while-printing, which is conducive to constructing spatially freeform geometries with high structural complexity and shape fidelity. The resultant 3D-printed polyorganosiloxane-based aerogels exhibit outstanding nanoporous performances, such as low density (0.14 g·cm−3), high surface area (484 m2·g−1), superhydrophobicity (water contact angle, 150°), high specific modulus (27.9 kN·m·kg−1), and low thermal conductivity (37.48 mW·m−1·K−1), which are ideal materials for shape-dominated thermal insulation applications. This work would provide an alternative printing strategy to fabricate nanoporous materials with arbitrary architectures for wider applications. [ABSTRACT FROM AUTHOR]

Abstract: Ultralow density (0.052gcm−3) carbon aerogels (CAs) were prepared for ultrahigh temperature thermal insulation, and their thermal conductivities were determined by laser flash method. The CAs have a total thermal conductivity as low as 0.601Wm−1 K−1, which is only one third of the value for closed-pore carbon foam (CF) with a density of 0.054gcm−3, at 2000°C under 0.15MPa argon. The solid, gaseous, and radiative conductivities of the CA are all much lower than those of the CF, because of the special nanoporous and pearl-necklace nanoparticle structures of the CA. The ultralow density CA clearly demonstrates its great potentials as thermal insulations for extreme applications. [Copyright &y& Elsevier]

• Polyvinylmethyldimethoxysilane was first used as polymer reinforcements. • A reticulate silica network structure was prepared. • The super-high specific surface area was 1479 ± 83 m2/g. • Reinforced silica aerogels exhibited elastic recovery properties. • Low thermal conductivity of 0.029 W/(m·K) was measured at ambient conditions. To overcome the interior brittleness of silica networks, polyvinylmethyldimethoxysilane reinforced methyltrimethoxysilane based silica aerogels (PRMSAs) were prepared via a facile strategy based on crosslinking polyvinylmethyldimethoxysilane with methyltrimethoxysilane in the sol-gel process and then drying in supercritical fluids. Benefiting from long-chain aliphatic hydrocarbons and abundant methyl groups, monolithic PRMSAs exhibit elastic recovery properties and super-high specific surface area, reaching up to 1479 ± 83 m2/g. As heat insulators, PRMSAs possess a low thermal conductivity of 0.029 W/(m·K) at ambient conditions. Our new method may greatly expand the usage of silica aerogels in thermal insulation applications. [ABSTRACT FROM AUTHOR]

Carbon aerogel is an attractive material for thermal insulation due to the porous character and high stability at high temperature. However, the wide application of carbon aerogel for thermal insulation is hindered by complicated supercritical-drying technology and high thermal conductivity of the pure carbon skeleton. Herein, a facile ambient-pressure-drying technology is developed for synthesizing Fe–N 4 doped carbon aerogel through catalyzing the polymerization reaction of monomers under a Fe sol, with copolymer F127 as enhancement phase for wet-hydrogel. The whole process does not have any solvent exchange or aging procedure. The prepared carbon aerogel has an ultralow thermal conductivity of 0.048 W/(m ∙ K) at room temperature, with negligible 2% shrinkage during ambient-pressure-drying process and excellent mechanical behavior with stress of 0.58 MPa at 10% strain. The thermal conductivity of carbon-fiber reinforcement carbon aerogel is 0.158 W/(m ∙ K) at 1100 °C, and has an elasticity modulus of 108.3 MPa. Based on an ideal model, density functional theory calculations reveal that doping Fe–N 4 can significantly enhance the anharmonicity of carbon-based materials and thus reduce the lattice thermal conductivity by more than 10 times. This work presents a facile and low-cost method for synthesizing carbon aerogel with single-atom doping for promising applications in thermal insulation. [Display omitted] • Fe–N 4 doped carbon aerogel is synthesized via a facile ambient-pressure-drying technology. • Thermal conductivity of carbon materials can be theoretically reduced more than 10 times by Fe–N 4 defects. • The carbon aerogel has a thermal conductivity of 0.048 W/(m ∙ K) at room temperature and 0.58 MPa compressive stress at 10% strain. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide aerogels (rGO aerogels) may become the next generation of thermal insulation materials. In this paper, the solid thermal insulation mechanisms of nitrogen-doped graphene aerogels (NDGA, rGO aerogels) were studied using nonequilibrium molecular dynamics simulations and experiments. The solid thermal resistance of NDGA is composed of the thermal resistance in graphene and the interfacial thermal resistance. Since the grain size of graphene in NDGA is much smaller than the phonon mean free path and the graphene sheet size, the defects and grafting play much more significant roles in lowering the thermal conductivity of graphene compared to sheet size. Vacancy defects show higher efficiency in lowering the thermal conductivity. Co-grafting and pyrrolic N addition further decrease the thermal conductivity. The interfacial thermal resistance of overlapped graphene is significant. It decreases with the increase of connection number. Bridging prevents the overlap of graphene, suppressing the heat transfer through overlap position. The thermal resistance in graphene plays a more significant role in the solid thermal insulation of NDGA compared to the interfacial thermal resistance. Overall, these findings provide a more thorough understanding of the solid thermal insulation mechanisms of NDGA. They are significant for the optimization and application of the aerogels. [ABSTRACT FROM AUTHOR]

Naturally-derived materials have attracted numerous attention owing to a unique native set of properties, but the significant shrinkage of biomass aerogel, from its final wet gel to aerogel, remains a formidable challenge. Here we explore a strategy based on supramolecular interaction and covalent crosslinking to overcome the inherent large shrinkage of chitosan aerogel, by reinforcing its molecular-level structure. The introduction of linear polyvinyl alcohol (PVA) chains can adequately interpenetrate with crosslinked chitosan chains to form strong intermolecular network architecture. Chitosan aerogel trussed with PVA enables to be readily fine-tuned, simultaneously giving rise to nano-sized cellular voids inside the aerogel. Chitosan aerogel obtained shows good heat insulation, applicable compressive property and exceptional processing feature of special-shaped components. We also find an emergent phenomenon that the addition of PVA may steer desirable orientation shrinkage, and linear elasticity at low strain in terms of chitosan aerogel. [ABSTRACT FROM AUTHOR]

Although carbon aerogels derived from naturally occurring materials have been developed extensively, a reasonable synthetic approach using cellulose-resource remains unclear. Here, we report a strategy to prepare carbon aerogels originated from cellulose position-selectively oxidized by TEMPO-oxidized process. Contrary to non-TEMPO-oxidized cellulose-derived carbon aerogels (NCCA) with relative loose structure, TEMPO-oxidized cellulose-derived carbon aerogels (TCCA) with tight fibrillar-continuous network are monitored, suggesting the importance of TEMPO-oxidized modification towards creating the architecture of subsequently produced carbon aerogels. TCCA endows a higher BET area despite owning slightly dense bulk density comparing with that of NCCA. The structural texture of TCCA could be maintained in a way in comparison to TEMPO-oxidized cellulose-derived aerogel, due to the integration and aggregation effect by losing the electric double layer repulsion via ionization of the surface carboxyl groups. FTIR and XPS analyses signify the evidence of non-functionalized carbon-skeleton network formation in terms of TCCA. Further, the mechanism concerning the creation of carbon aerogels is also established. These findings not only provide new insights into the production of carbon aerogels but also open up a new opportunity in the field of functional carbon materials. [ABSTRACT FROM AUTHOR]

Aerogels with oriented sheets show better thermal insulation properties. However, it is difficult to prepare bulk oriented aerogels. In this paper, we prepared this kind of aerogels by using aligned fibers as the wall of galleries. This simple method makes the N-doped graphene sheets align along the in-plane orientation during impregnating. The as-prepared aerogel composites not only show much lower through-plane thermal conductivity (26.6–29.8 mW m −1 K −1 ) compared to their in-plane thermal conductivity (44.9–55.1 mW m −1 K −1 ), but also exhibit high tensile strength (higher than 3 MPa). After being heat treated at 300 °C, the through-plane thermal conductivity (23.3 mW m −1 K −1 ) is even lower than the thermal conductivity of pure aerogels. These properties significantly contribute to their applications in thermal insulation. Besides, the simple method is also useful in preparing other materials with oriented sheets and high strength. [ABSTRACT FROM AUTHOR]

Gaseous thermal conductivity takes up a great proportion of the thermal conductivity of aerogels. In this work, we present a new strategy to restrain the gaseous thermal conductivity, using 3-dimension nanoporous aerogels from 2-dimension sheets. Experimental results show that the N-doped graphene aerogels, typical nanoporous aerogels from 2-dimension sheets, exhibit very low gaseous thermal conductivity (12.58 mW m −1 K −1 at room temperature) at extremely low bulk density (0.0320 g cm −3 ), suggesting that the nanoporous aerogels from 2-dimension sheets can restrain the gaseous thermal conductivity more efficiently than that from 0-dimension pearls. This finding may significantly contribute to the next generation of thermal insulation materials with lower thermal conductivity and much lower density. [ABSTRACT FROM AUTHOR]

Naturally occurring polymer-based aerogels have myriad practical utilizations due to environmentally benign and fruitful resources. However, engineering morphology-controllable biomass aerogels still represents a great challenge. Here we present a facile solution to synthesize chitosan aerogels having distinguished textures by reacting oxidized chitosan with formaldehyde and chitosan sol. In more detail, chitosan was chemically oxidized using two types of oxidation agents such as ammonium persulphate (SPD) and sodium periodate (APS) to obtain corresponding oxidized chitosan, subsequently cross-linked with chitosan solution containing formaldehyde to harvest SPD-oxidized chitosan aerogels (SCAs) and APS-SPD-oxidized ones (ASCAs) after aging, solvent exchange and supercritical drying processes. We found that the morphologies of as-prepared chitosan aerogels are strongly dependent upon the oxidation pattern towards chitosan. The structural textures of SCAs and ASCAs appear nanoflake-like and nanofiber-like structures, which may be related to spatial freedom of active groups located in chitosan. Selected area electron diffraction analysis reveals that the crystalline properties of chitosan aerogels generally appear the serious deterioration comparing to raw chitosan owing to their interconnected skeletal structure formation. The occurrence of characteristic groups displays cross-linked chain construction by using chemical state measurements such as FT-IR and XPS. Further, a plausible mechanism for controlling morphology of chitosan aerogels is also established. This new family of method for creation of chitosan aerogels may open up a perspective for biomass aerogels with controllable textures. [ABSTRACT FROM AUTHOR]

Acquiring high specific surface area (SSA) is a crucial reason why aerogels possess diverse unusual functionalities both in nanoscale structures and macroscopic properties. Although biomass aerogels can remedy the mechanical brittleness in contrast to conventional silica aerogels, regrettably causing a major decrease in SSA aspect. Here we present a generalizable synthetic means towards a family of chitosan aerogels (CAs) with large internal surface area, originating from chitosan sols in ethanol/water binary medium. The as-prepared CAs show high SSA of 973 m 2 g −1 , appropriate texture homogeneity and thermal stability, attributing to uniformly inter-associated structures. We found an emergent phenomenon that free-standing wet chitosan gel could be still produced despite greatly lowering its substance concentration, attesting the remarkable role of ethanol for promoting gelatum formation. This enhancement to gelation is due to the introduction of micro-dispersed active phases upon ethanol/water excitation, easily forming fine interconnected skeletons of CAs. The adsorption tests of CAs for abatement of methyl orange (MO) verify that dye-treated water almost recovers into pure one, well in line with the evidence of high SSA CAs. A convincing explanation for gelling and cross-linking is also analyzed. Our work facilitates to explain the generation mechanism of gels in binary solvents for the creation of CAs with high SSA. [ABSTRACT FROM AUTHOR]

Lightening thermal insulation system is significantly crucial for the high-cost aerospace field. This paper prepared novel thermal insulation composites, N-doped graphene aerogels reinforced by ultrafine quartz fibers. The density is only 0.072 g/cm 3 , and the thermal conductivity measured by Hot disk apparatus is 0.0327 W/(m K). Meanwhile, with reinforced by ultrafine quartz fibers, the tensile strength of the composites reaches 3.61 MPa. The ultralow density, low thermal conductivity and high strength make the composites potentially useful thermal insulation materials in the aerospace field. [ABSTRACT FROM AUTHOR]

We report on the relationship for structure, compression and thermal insulation properties of cellulose diacetate-based aerogels (CDBAs), prepared from cellulose diacetate (CDA) cross-linked with 2, 4-toluene diisocyanate (TDI) by using sol-gel and supercritical drying processes. Lower reactant dosage (no matter CDA or TDI), can induce smaller shrinkage (~12%) after supercritical drying, and even to achieve lower density (~0.06 g/cm3) of CDBAs. Monolith CDBAs have typical three-dimensional networks with lamella reinforced fiber-like skeletons and nanometric pores. Such reinforced networking structure with lamellas as reinforcement is responsible for the maximum compression strength of ~1.29 MPa at 10% strain and compressive modulus of 21.86 MPa in CDBAs. Besides, the excessive addition of TDI leads to accelerate the growth of secondary fiber-like skeletons to ultimately divide the large pores into the small ones inside the formed network. This structural evolution enables to synergistically reduce gaseous thermal conductivity by means of Knudsen effect and increase that of solid part due to wider solid contacted area. The minimum total thermal conductivity of ~0.0313 W m−1 K−1 at ambient environment is obtained when the synergetic effects reach up to the critical balance, whose solid and gaseous proportions are calculated as 51.76 and 48.24%, respectively. Unlabelled Image • Cellulose diacetate-based aerogels (CDBAs) were prepared by crosslinking with isocyanate groups. • Reinforced networking structure is responsible for the high compressive strength of CDBAs up to ~1.29 MPa at 10% strain. • CDBAs with fiber-like skeletons can greatly reduce gaseous thermal conductivity by Knudsen effect. [ABSTRACT FROM AUTHOR]