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Effective thermal superinsulation in extremely high temperatures (EHT) is crucial for aerospace, industrial, and civilization activities. However, current strategies relying on ceramic materials face limitations due to their high thermal conductivity and brittleness in specific conditions. In this study, a feasible and scalable method for synthesizing a flexible, lightweight, and transformable fire‐reborn silica‐alumina hybrid ceramic aerogel (FR‐SACA) is presented, which is achieved by rearranging silica aerogel microparticles and Al2O3 ceramic fibers using a self‐sacrifice polymer, resulting in a bio‐inspired bird nest structured FR‐SACA. The SACA exhibits exceptional properties, including an ultra‐low density of 0.01 g cm−3, a low thermal conductivity of 0.029 W m−1 K−1, and a reversible compression of up to 80%. Notably, a 20 mm‐thick FR‐SACA demonstrates a remarkable temperature reduction of 1179.6 °C when exposed directly to a 1300 °C flame, suggesting its potential as a thermal superinsulation material in EHT environments. Furthermore, the transformability of SACA enables in situ fabrication on surfaces with diverse heteromorphic structures, such as flat, bent, and angled shapes, thereby providing thermal superinsulation for various constructions. The Phoenix Nirvana process opens up new possibilities for synthesizing ceramic aerogels with desirable flexibility and adaptive properties, facilitating effective thermal management under extreme conditions. [ABSTRACT FROM AUTHOR]

Highlights: Curving 2D MXene into 1D nanofibers can effectively stop the restacking of MXene flakes, and then the nanofibers are used to construct a lightweight and multifunctional MXene/C aerogel. The MXene/C aerogels achieved an RLmin of − 53.02 dB and EAB of 5.3 GHz. The radar cross-sectional reduction value of MXene/C aerogels can reach 12.02 dB m2. Integrating multiple functions such as thermal insulation, sensing, and microwave absorption into one material—MXene/C aerogel. Two-dimensional transition metal carbides and nitrides (MXene) have emerged as promising candidates for microwave absorption (MA) materials. However, they also have some drawbacks, such as poor impedance matching, high self-stacking tendency, and high density. To tackle these challenges, MXene nanosheets were incorporated into polyacrylonitrile (PAN) nanofibers and subsequently assembled into a three-dimensional (3D) network structure through PAN carbonization, yielding MXene/C aerogels. The 3D network effectively extends the path of microcurrent transmission, leading to enhanced conductive loss of electromagnetic (EM) waves. Moreover, the aerogel's rich pore structure significantly improves the impedance matching while effectively reducing the density of the MXene-based absorbers. EM parameter analysis shows that the MXene/C aerogels exhibit a minimum reflection loss (RLmin) value of − 53.02 dB (f = 4.44 GHz, t = 3.8 mm), and an effective absorption bandwidth (EAB) of 5.3 GHz (t = 2.4 mm, 7.44–12.72 GHz). Radar cross-sectional (RCS) simulations were employed to assess the radar stealth effect of the aerogels, revealing that the maximum RCS reduction value of the perfect electric conductor covered by the MXene/C aerogel reaches 12.02 dB m2. In addition to the MA performance, the MXene/C aerogel also demonstrates good thermal insulation performance, and a 5-mm-thick aerogel can generate a temperature gradient of over 30 °C at 82 °C. This study provides a feasible design approach for creating lightweight, efficient, and multifunctional MXene-based MA materials. [ABSTRACT FROM AUTHOR]

Silica aerogels, a type of porous material featuring extra low density and thermal conductivity, have drawn increasing interest from both academia and industry owing to their excellent thermal insulation performance. However, thermal insulation is always the single consideration when silica aerogels are used for thermal management. In this study, the on‐demand thermal management (ODTM) of silica aerogel with either passive thermal insulation, passive heating, or passive cooling in different environments is revealed. The ODTM behavior of silica aerogels can be simply fulfilled through their optical property variations such as solar light transparency and infrared emissivity, which are controllable via the microstructures of the building blocks and surface composition design. Robust solar heating of 25 °C higher than the ambient in the daytime and sub‐ambient cooling of 7 °C at night is achieved with the traditional transparent silica aerogel. Interestingly, sub‐ambient cooling of 5 °C in the daytime and a warmer state on cold nights is achieved by modifying its solar transmittance and infrared emissivity. This study guides a comprehensive understanding of the thermal management behavior of silica aerogels and leads to ODTM applications of silica aerogels by tailoring their optical and thermal conductivity properties. [ABSTRACT FROM AUTHOR]

Personal thermal management (PTM) materials have attracted increasing attention owing to their application for personal comfort in an energy‐saving mode. However, they normally work in the same media such as in the air, and little is known about what will happen in other media like water. In this study, a system for cross‐media thermal management (CMTM): passive cooling in air and thermal insulation underwater is proposed. Hybrid aerogels comprising thermoplastic polyurethane (TPU) matrix and superhydrophobic silica aerogel particle (SSAP) for CMTM are designed and synthesized using a thermally induced phase separation and self‐templating strategy. The TPU matrix endows the aerogels with super stretchability (500%), shape memory, and outstanding healing recovery rate (89.9%), which are ideal characteristics for potential wearable usage. Additionally, the TPU and SSAP endow the aerogel with high solar reflectivity and infrared emissivity, thus achieving a sub‐ambient cooling of 10.6 °C in air. Moreover, the SSAP endows the aerogels with low thermal conductivity (0.052 W m−1·K−1) and high hydrophobicity (143°), enabling the aerogels for underwater thermal insulation. The CMTM performance of the aerogels makes them for potential uses in cross‐media environments such as reefs and islands where cooling in air and thermal insulation in water are required. [ABSTRACT FROM AUTHOR]

Silica aerogels are one of the most widely used aerogels, exhibiting excellent thermal insulation performance and ultralow density. However, owing to their plenitude of Si-O-Si bonds, they possess high infrared emissivity in the range of 8–13 µm and are potentially robust passive radiative cooling (PRC) materials. In this study, the PRC behavior of traditional silica aerogels prepared from methyltrimethoxysilane (MTMS) and dimethyldimethoxysilane (DMDMS) in outdoor environments was investigated. The silica aerogels possessed low thermal conductivity of 0.035 W/m·K and showed excellent thermal insulation performance in room environments. However, sub-ambient cooling of 12 °C was observed on a clear night and sub-ambient cooling of up to 7.5 °C was achieved in the daytime, which indicated that in these cases the silica aerogel became a robust cooling material rather than a thermal insulator owing to its high IR emissivity of 0.932 and high solar reflectance of 0.924. In summary, this study shows the PRC performance of silica aerogels, and the findings guide the utilization of silica aerogels by considering their application environments for achieving optimal thermal management behavior. [ABSTRACT FROM AUTHOR]