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Lightweight phenolic matrix composites are highly potential in ablative thermal protective materials for future aerospace vehicles, and hybrid modification is considered as one of effective ways to improve the oxidation and ablation resistance of phenolic matrix. Herein, the co-continuous silica zirconium hybrid phenolic resin (SZRx) was synthesized, which can be used to prepare lightweight ablation resistant aerogel composites by the sol-gel method. The SZRx aerogel showed stable porous structure and excellent hydrophobicity, and the silicon zirconium hybrid greatly improved the high temperature carbon residue and oxidation resistance of phenolic resin. The SZRx aerogel composites also possessed excellent integrated characteristics of heat protection and insulation, with a linear ablation rate as low as 0.032 mm/s and a back temperature below 200 °C. The synergistic effect of silicon and zirconium formed the multiphase ceramic layer (C, SiO 2 , SiC and ZrO 2) with the sea-island-like structure on the surface of the composite material, which can effectively resist high-temperature ablation and aerodynamic exfoliation. This can indicate that silicon zirconium dual element hybrid phenolic resin is the highly competitive matrix for lightweight and ablation resistant composite materials. [Display omitted] [ABSTRACT FROM AUTHOR]

Lightweight ablative materials owing to their low density, high efficiency heat insulation and excellent designability, which are considered as the most promising candidate materials in the field of aerospace ablative thermal protection. In this work, a polycarbosilane (PCS) in-situ reinforced carbon felt/phenolic (PR/C f) aerogel composite is reported. The surface of aerogel and carbon fiber was coated with PCS protective layer by sol gel method and secondary vacuum impregnation process. The aerogel composite material possesses low density (0.264–0.307 g/cm3), hydrophobic, low thermal conductivity (0.121–0.178 W/(m·K)) and significant high compressive strength (12.89 MPa). When the oxygen acetylene flame with high heat flow density ablates for 20 s, it shows high efficiency in heat protection and insulation, and the linear ablation rate is as low as 0.089 mm/s. The PL/PR/C f aerogel composite shows competitive and broad application prospects in the field of ablation heat protection in the future. [ABSTRACT FROM AUTHOR]

In this study, we investigated the tunable porous structure of SiCN(O)-derived ceramic aerogels by changing the molecular structure of the polysilazanes from linear to branched. We also studied the effect of molecular structure on the thermal insulation properties of ceramic aerogels. As the percentage of branched molecular structure in the polysilazane precursor increased, the internal microscopic pore structure of the aerogels changed from macroporous to mesoporous. The specific surface areas and pore volumes of the ceramic aerogels prepared with different precursors increased after pyrolysis at 1000 °C, ranging from 3.7 to 255.9 m2/g and 0.01–0.36 cm3/g, respectively. The corresponding thermal conductivities increased slightly as the aerogels contracted after pyrolysis. The low thermal conductivity (0.046 W/(m·K) at minimum) can be attributed to the decrease in pore size caused by adjusting the precursor structure, which limits the thermal conduction of gas in the porous aerogel materials. [ABSTRACT FROM AUTHOR]

Thermal camouflage is one of the most effective ways to guarantee the security and survival of military objects against infrared (IR) detectors. However, with the rapid development of IR detection technology, the IR thermal camouflage of objects and weapons has become more and more difficult, and advanced thermal camouflage materials are urgently needed to meet the demands of warfare. So far, two dimensional (2D) nanomaterials have demonstrated excellent performances with low IR emissivity, optoelectronic tunability, and compatible stealth capabilities. Among them, graphene and MXenes are the most attractive 2D materials used for thermal camouflage applications. Here we present a review of recent progress on the thermal camouflage properties of graphene and Ti 3 C 2 T x MXene in the form of composite film, microcapsule and aerogel structures, a summary of current understanding of the working principle of thermal camouflage materials, and current limitations and future opportunities in graphene and Ti 3 C 2 T x MXene research and development. [ABSTRACT FROM AUTHOR]

Flexible pressure sensors embody outstanding mechanical and sensing performance, particularly in the fields of personal health monitoring and artificial intelligence, while catering to multifunctional applications resilient against harsh weather conditions. Among these, Ti 3 C 2 T x MXene-based aerogel materials with high surface area and excellent conductivity have attracted a lot of attention. However, there are big challenges in improving the mechanical properties at low densities and designing multi-level pore structures. Herein, the prepared silane monomers (MP) are firstly synthesized by 3-(Trimethoxysilyl) propyl methacrylate (MPTES) and polyethylene glycol diacrylate (PEGDA), then polydopamine-modified silicon dioxide (PDA-SiO 2) nanofibers employed with MXene nanosheets form covalent cross-linking nanofiber aerogels. The multi-level stable structure improves both mechanical strength and elasticity. The assembled MXene/MP/PDA-SiO 2 pressure sensors exhibit a high sensitivity of −0.83 kPa−1, a rapid response time of 48 ms, a minimum 1 % strain detection limit, and reliable stability over 10,000 cycles. Furthermore, these sensors can be used for human motion detection and health diagnostics, and show good personal thermal management performance. This work holds a promising candidate for the next generation of multifunctional flexible electronic devices. [ABSTRACT FROM AUTHOR]

Aerogels are excellent thermal insulation materials with extremely low thermal conductivity. However, the practical applications of traditional oxide aerogels, such as SiO 2 and Al 2 O 3 aerogels, are limited by the disadvantages of easy sintering and intrinsic brittleness. SiC is a good candidate for new aerogel due to its superior stability and good properties from room to high temperatures. However, it is generally supposed that SiC cannot be employed as thermal insulation material because of its high intrinsic thermal conductivity. We herein developed SiC nanowire aerogel with quite low thermal conductivity using freeze-drying method. The fabricated SiC nanowire aerogel exhibits ultra-high porosity (∼99.5%), excellent high-temperature stability (∼1700 °C), extremely low thermal conductivity (0.035 W/(m⋅K)) and good compressive flexibility. The low thermal conductivity is resulted from ultra-high porosity and multi-level nanostructures. Flexible compression behavior is attributed to the capability of moving and buckling of SiC nanowires, originating from both ultra-high porosity and strong connection between nanowires. This exploration highlights the flexible SiC nanowire aerogel as a promising high temperature thermal insulation material. [ABSTRACT FROM AUTHOR]

Laser technology has made great progress over the past decades. However, corresponding defense systems have lagged slightly behind. Therefore, there is significant room for research with respect to the principles and bases of existing laser protective materials. In this paper, a kind of silica aerogel material is prepared with the acid-base sol-gel process. Considering the influence of thermal conductivity and the porosity of the aerogel materials on the laser irradiation results, the best laser resistance times of the materials were obtained. The concept of the maximum energy transfer radius is proposed to build a preliminary laser irradiation model for porous materials. It indicates that under the irradiation of a continuous wave laser with a power of 7 kW·cm−2, the silica aerogel materials with the thickness of 3, 6, and 9 mm can withstand the laser for maximum times of 26, 61, and 100 s, respectively. After 7 s of irradiation, the surface temperature of 3 mm from the laser incident point is 226.9 °C. Aerogels, especially silica aerogels, should be considered as future laser protection materials. The extremely low thermal conductivity and the strong scattered ability for laser of these materials will provide a good defensive effect against large-energy laser weapons. [ABSTRACT FROM AUTHOR]

[Display omitted] • Porous coral-like Co/CoO/RGO hybrid aerogels are successfully developed. • The special structure brings multiple loss modes and good impedance matching. • Achieving high EM wave loss, hydrophobicity and thermal insulation properties. • DFT simulations are adopted to verify the interface polarization of interfaces. Addressing the growing issue of electromagnetic radiation calls for urgent exploration of effective electromagnetic wave absorbers. Herein, a series of coral-like Co/CoO nanoparticles/reduced graphene oxide (Co/CoO/RGO) hybrid aerogels were synthesized via a freeze drying-thermal reduction strategy. Their advantages involving porous interconnected framework, abundant heterogeneous interfaces, and integration of dielectric/magnetic units could bring multiple loss modes. By manipulating the Co(CO 3) 0.5 (OH)·0.11H 2 O (CCOH) addition and reduction temperature, the electromagnetic parameters could be tuned, ultimately resulting in optimal absorption capability with maximal reflection loss of –32.4 dB and effective bandwidth of 4.2 GHz. More importantly, excepting the high electromagnetic wave loss, Co/CoO/RGO hybrid aerogels also exhibit good hydrophobicity and thermal insulation properties, making them suitable for application in harsh environment. Besides, the special structure and multiple components lead to multiple heterointerfaces in aerogels, the resultant interface polarization is deemed to contribute to electromagnetic wave loss. Here, Density Functional Theory (DFT) simulation based on first-principles is adopted to verify the contribution of interface polarization from the theoretical level. According to the simulation results, the electron-occupied states near the Fermi level are significantly different among the different phases comprising the heterointerfaces, and there is a noticeable accumulation of charge at these interfaces, successfully affirming the interface polarization behavior at different interfaces. [ABSTRACT FROM AUTHOR]

• Monolithic samples were fabricated using a rapid supercritical extraction process. • Small-scale prototype glazing system with thin aerogel pane were fabricated. • Influence of aerogel on optical, thermal, and color rendering performance is investigated. • Thermal transmittance reduction up to 28% was calculated with a small loss in light transmittance. • Thin aerogel tends to make the colors brighter and to involve small color shift variations. Thin monolithic aerogel is one of the most promising super-insulated thermo-acoustic and lighting materials for use in highly energy-efficient windows. This study investigates the influence of 3-mm monolithic aerogel in the gap of small-scale prototype glazing systems on optical, thermal, and color rendering performance. Data available in the literature are in general related to monolithic aerogel panes with a thickness greater than 10 mm; only a few studies investigate thin aerogels. The novelty of the paper is the investigation of thin aerogel physical properties focusing on 3 mm – thick panes sandwiched in double glazing systems. The aerogel samples were fabricated at Union College using a rapid supercritical extraction method, reducing the time of fabrication for monoliths. Peak values of visible spectral transmittance in the 0.75 – 0.78 range were measured using a conventional spectrophotometer in the 300–2500 nm wavelength range. A thermal transmittance reduction of up to 28% was calculated for the glazing systems with the aerogel. The effect of the thin aerogel glazing systems on color rendering observed through transparent material was evaluated following a new measurement methodology developed in previous work. The results showed that the innovative solutions with thin aerogel tend to make the colors brighter and involve slight color shift variations, resulting in high Color Rendering Index values (85 – 88). [ABSTRACT FROM AUTHOR]

• Graphene/Fe3O4 hybrid aerogel were prepared by self-assembly synthesis. • The effects of concentration of nano-Fe3O4 in the aerogel were studied. • Mechanical and thermal properties of the hybrid aerogels were investigated. [Display omitted] Graphene aerogel and graphene-magnetite hybrid aerogel were prepared using hydrothermal method followed by a freeze-drying process. Magnetite nanoparticles were encapsulated by graphene sheets in an electrostatic self-assembly process. The morphology and properties of aerogels were characterized by several techniques including UV-Vis spectroscopy, Raman spectroscopy, FESEM, TEM and XRD. The mechanical and thermal behavior of the aerogels were evaluated at different concentration levels of Fe 3 O 4 nanoparticles (0, 10, 20 and 30 wt%). The compressive strengths of the hybrid aerogels at the strain of 80% for graphene aerogels containing 0, 10, 20 and 30 wt% Fe 3 O 4 nanoparticles were determined to be 5.93, 12.96, 6.85, and 6.15 kPa, respectively. The highest mechanical properties were achieved for the sample containing 10 wt% Fe 3 O 4 nanoparticles (FGA10). Thermal analysis revealed that FGA10 sample had a 15% less weight loss when heated up to 600 °C compared with that for the bare graphene aerogel, indicating the formation of a more thermally stable structure. Furthermore, adding Fe 3 O 4 nanoparticles improved the thermal insulation performance of the graphene aerogel, since the dynamic heat transfer rate and heat dissipation rate of FGA10 were lower than those for the bare graphene aerogel. [ABSTRACT FROM AUTHOR]

Although graphene-based composites have been considered desirable candidates for thermal management applications, their poor electrical insulation restricts their further use in electrical insulation requiring occasions. Fluorinated graphene (FG), a new type of graphene-based material, attracts the attention of researchers due to its excellent electric insulation property. In this work, a novel fluorinated graphene aerogel/polydimethylsiloxane (FGA/PDMS) composite with a tightly-packed structure is constructed via freeze-drying and vacuum impregnation. The fabricated composite shows high compressibility and superior thermal conductivity of 1.41 W/(m·K) with a relatively low FGA loading of 0.28 wt%, 605.6% larger than the original PDMS. Meanwhile, it also maintains excellent insulation properties with an ultra-low electrical conductivity of 2.0 × 10−9 S/cm. 180 times smaller than graphene aerogel/PDMS. The practical excellent heat dissipation performance of the composite functioning as thermal interface material is also verified by a thorough study theoretically and experimentally. Furthermore, the FGA/PDMS composite also behaves with excellent flame retardant properties. [Display omitted] • Fluorinated graphene aerogel/polydimethylsiloxane (FGA/PDMS) with a tightly-packed structure is constructed. • FGA/PDMS shows lightweight and excellent compressibility. • FGA/PDMS has a low electrical conductivity of 2.0 × 10−9 S/cm. • FGA/PDMS exhibits impressive flame retardant properties at 1982 °C. [ABSTRACT FROM AUTHOR]

[Display omitted] • Low cost and high performance. • Silica aerogel fabricated from incineration bottom ash. • Thermal insulation paint with silica aerogel additive. • 12 °C surface temperature reduction improvement on the heated plate at 60 °C. • 1 °C in-chamber temperature reduction with external temperature of 44.6 °C. In this work, silica aerogel (SA) powder is fabricated through a sustainable method from incineration bottom ash. The fabricated SA has a low thermal conductivity of 0.025 W/mK, high surface area of 786 m2/g, and high porosity of 96.36%. The thermal analysis of SA powder shows it has a stable hydrophobicity up to 418 °C. The SA powder has been mixed into water-based paints to develop a high efficient thermal insulation paint with inproved thermal insulaton properties. Different percentage of SA were mixed into the paint samples to prepare the silica aerogel thermal insulation paint (SATIP) and their physical properties were studied. The SATIP samples were then coated on cement board substrates. The thermal conductivity, water resistance, durability and insulation performance of the samples were investigated and evaluated systematically. The scrub resistance of SATIP can be improved significantly by 219% after adding 5 vol% SA powder. And by adding 20 vol% of SA into the SATIP, it achieves up to 12 °C surface temperature reduction improvement compare to the one without SA on the heated plate at 60 °C, and 1 °C in-chamber temperature reduction with external temperature of 44.6 °C. The spectral reflectance analysis demonstrates that the improvement of the thermal insulation performance of the SATIP is attributed to the thermal insulation property of SA and proves that the developed SATIP is color insensitive and has wider applications. The results demonstrated a low-cost and scalable process fabricates SA with superor properties. The developed SATIP has a great potential for application in sustainable and green buildings for energy saving. [ABSTRACT FROM AUTHOR]

• Unidirectional anisotropic PIAs have been prepared by freeze-drying. • The PIA shows excellent thermal stability and stable mechanical behavior. • The u -PIA-6 exhibits great strength, which is over twice as high as that of the TEEK-HH at 177 °C with a similar density. • The u -PIA shows great thermal insulation properties in anisotropic. Polyimide aerogels (PIAs) are the new type of high-performance lightweight material that combines the excellent thermal and mechanical behavior of polyimides with the highly porous and lightweight properties of aerogels. PIAs can meet the increasing material requirements of high-tech fields such as the aerospace and transportation industries. This study reports a series of all-aromatic anisotropic polyimide aerogels (p-phenylenediamine (PDA) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA)) with unprecedented behavior. These PIAs were synthesized using a random or unidirectional freeze-drying method followed by thermal imidization of the precursor solution. Their mechanical and thermal conductivity performance were anisotropic (u -PIA-8 strength: 1.86 and 0.14 MPa, thermal conductivity: 62.9 and 50.1 mW·m−1·K−1 along the axial and radial direction, respectively). Furthermore, the PIAs possessed excellent compression behavior in a wide temperature range from 25 °C to 316 °C, with a compressive strength over twice that of the commercial polyimide foam TEEK-HH (u -PIA-6 strength: 0.83 and 0.32 MPa at 177 and 316 °C, TEEK-HH strength: 0.31 MPa at 177 °C). These aerogels also demonstrated good thermal insulation performance after being held at 300 °C for 20 min (u -PIA-8: 76.3 °C at 25 mm). These highly anisotropic aerogels exhibit flexible thermal protection properties that extend the potential use of PIAs to applications such as high-temperature-resistant rocket fairings, sandwich structures, and arc-shaped structures for aerobats or the automobile industry. [ABSTRACT FROM AUTHOR]

Lightweight and multiscale nanocomposites are considered to be the most promising materials applied in the field of advanced aerospace and modern building industry, owing to their outstanding mechanical, thermal and flame-resistant properties served in high-temperature oxidizing environments. Herein, a novel siliconoxycarbide (SiOC) modified needle quartz fiber felt reinforced phenolic resin nanocomposite (SiQF/PR) with a hierarchical macro-/micro-/nano-scaled structure is reported. The as-prepared highly porous SiQF/PR nanocomposite exhibits a multiscale three-dimensional network and the micro-sized SiOC particles, derived from the hydrolysis of methyltrimethoxysilane (MTMS) and dimethyldiethoxysilane (DDS), are uniformly incorporated into the phenolic aerogel. The resultant nanocomposite has a bulk density of 0.30–0.35 g/cm3, and the maximum compressive strength reaches 4.20 MPa and 3.34 MPa in xy and z directions, respectively. Thermal stability and oxidation resistance experiments show that the SiQF/PR multiscale composite has a good ablation and heat insulation performance under oxyacetylene test condition, and the backside temperature of SiQF/PR is only 55.5 °C under 1.8mw/m2 for 120 s, and line ablation rate of SiQF/PR multiscale nanocomposite decreases by 20.1% at 1.8 MW/m2 and 59.5% at 0.4 MW/m2 compared to non-SiOC modified composite. These results indicate that the lightweight SiQF/PR nanocomposite fabricated by this method is very suitable for architectural or aerospace applications as high-performance insulation material. [Display omitted] [ABSTRACT FROM AUTHOR]

Biomass-derived aerogels have received extensive attention as potential thermal management materials for energy-efficient buildings. However, it remains a huge challenge to fabricate a fully bio-based aerogel with excellent mechanical property, flame retardancy, and low thermal conductivity. Herein, we demonstrate a novel and facile strategy to manufacture a fully biomass-based aerogel from naturally abundant ammonium alginate (AL) and phytic acid (PA), in which PA acting as both flame retardant and cross-linking components constructs a strong network with AL matrix. Consequently, the resultant biomass aerogel with a low density of 0.052 g/cm3 exhibits ultrahigh mechanical modulus (25.1 ± 3.1 MPa) and specific modulus (440.4 ± 54.4 MPa cm3·g−1), much superior to those of biomass aerogels ever reported. Due to the existence of the uniform three-dimensional porous network, the biomass aerogels exhibit low thermal conductivity (34–38 mW/m·K) and excellent thermal insulation performances. Further, the introduction of PA endows the aerogel with high flame retardancy (limiting oxygen index value of 57%, UL-94 V-0 rating, and extremely low heat release), while the biodegradability of the materials keeps at a high level with a biodegradation rate of 91.43%. Combining with the advantages of mechanically strong property, high flame retardancy, excellent thermal insulation, and biodegradation, the aerogel of this work provides a new strategy to fabricate thermal insulation materials with high environmental safety. [Display omitted] [ABSTRACT FROM AUTHOR]

A nanoporous rubber aerogel (NRA) is fabricated successfully using recycled textile fibers (RTFs) from car tire wastes, polyvinyl alcohol (PVA) via freeze-drying. The NRA exhibits a low density (down to 0.025 g/cm3), a high porosity (up to 98%), a robust mechanical property with the compressive resistance at 10% deformation above 20 kPa, a high oil-absorption capacity (up to 18 g/g), low thermal conductivity (down to 35 mW/m-K), and a high noise reduction coefficient (NRC value of up to 0.55). In our study, the production time is reduced significantly from 48 h to 17 h compared to previous works. More importantly, the central composite design and response surface methodology are applied to investigate the effect of the RTFs and PVA contents on the volume shrinkage, density, porosity, compressive resistance, oil absorption capacity, and thermal conductivity. As a result, it is found that the contents of RTFs and PVA should be in the range of high-level (4.0–5.0 wt%) and low-level (1.0–1.5 wt%), respectively. In addition, the effect of thicknesses and compositions on the sound absorption property of the NRA is further discussed using the analysis of variance (ANOVA). A higher noise reduction coefficient (NRC) is attained at a large thickness for compositions 1 (5.0 wt% RTFs, 1 wt% PVA). The sound absorption coefficient of the NRA in the high frequencies (1000–6000 Hz) is relatively high, and for the low- and medium frequencies (125–1000 Hz) relatively low. As a result, the NRA can be a potential candidate for oil-spill cleaning, heat-insulating and sound absorbing applications. [Display omitted] • NRA is fabricated successfully aerogel via a time-saving method. • NRA has an ultra-low density, a high porosity, and a robust mechanical properties. • NRA can be a potential material for oil absorption applications. • NRA can be a potential material for thermal insulation applications. • NRA can be a potential material for sound absorption applications. [ABSTRACT FROM AUTHOR]

In this study, CNT-doped carbon aerogel (CNT-CA) and carbon aerogel (CA) were used in different weight ratios (0.1, 0.3, and 0.5 wt%) to reinforce epoxy (Ep) nanocomposites. The relationship between the aerogels' structure deformation such as the average diameter, the total volume of pores, specific surface area, and interfacial (particle/matrix) interaction, distribution, rheological, mechanical, and thermal properties were investigated systematically. Also, the nanocomposites were investigated by ATR-FTIR, XRD, and Raman spectroscopy. In general, the fabricated nanocomposites showed enhanced properties compared to the neat epoxy which is attributed to the penetration of polymer chains into the porous three-dimensional structure of the distributed aerogels. This phenomenon resulted in a high filler/matrix interaction, resulted in a better load transfer. Ep/CNT-CA showed better properties than Ep/CA which is due to ultrahigh specific surface area in CNT-CA. The rheological analysis showed a significant change in behavior from a liquid-like state to a pseudo-solid state in Ep/CA0.3 and Ep/CNT-CA0.1. Mechanical and thermal investigations of nanocomposites showed 8–17% increment in young modulus, 39–52% in tensile strength, 47–69% in elongation at break, 28–53% in E′ at 40 °C, 2–6% in Tanδ, and 7–11 °C in T max (compared to the neat epoxy matrix). [Display omitted] • CNT-doped carbon aerogel was used as reinforcement in epoxy matrix. • Rheological properties of carbon aerogel/epoxy suspensions were investigated and evaluated with rheological parameters. • Physical, morphological and mechanical characterizations were performed on nanocomposite samples. • Physical structure of the aerogel was an effective parameter on the nanocomposite performance. • Penetration of the resin caused a high interaction with the large surface area of aerogels' mesoporous structure. [ABSTRACT FROM AUTHOR]

Advanced composite aerogel materials have attracted much attention due to the unique structure and properties. However, the efficient manufacturing process and structural stability were still a challenge. Herein, a novel hydroxyapatite nanowires/polyimide (HAnws/PI) composite aerogel was synthesized by the ultralong HAnws combined with polyamic acid via directional freezing and thermal imidization. Among them, the HAnws and PI intertwined to form a three-dimensional network structure, which decreased the volume shrinkage of aerogel in thermal imidization from 42.9% to 12.6%, resulting in high porosity (>96%) and low density (0.0329–0.0431 g cm−3). In addition, the HAnws/PI aerogel with layered porous structure exhibits obvious anisotropic mechanical properties. The axial specific modulus as high as 78.05 kN m kg−1 and radial high elasticity can withstand 100 cycles of fatigue resistance. Moreover, the lowest radial thermal conductivity at 32.21 mW m−1 K−1 and the maximum of the anisotropy factor was 2.2, which was very suitable for insulation pipes to prevent additional heat loss. Therefore, the novel nanofibers reinforced organic aerogel was expected to provide more abundant functional applications in energy efficiency. [Display omitted] • HAnws can effectively inhibit the volume shrinkage of HAnws/PI aerogel. • The composite aerogel with tubular pores was prepared by directional freezing. • HAnws/PI aerogel exhibited anisotropic mechanical properties and thermal insulation. • HAnws/PI aerogel showed a low radial thermal conductivity and the maximum of the anisotropy factor was 2.2. [ABSTRACT FROM AUTHOR]