WANG Mengmeng, LIU Ruixiang, QI Kaiyu, ZHANG Jingsheng, LIU Honghua,

CAO Junchang, LI Zhanfeng, SUN Chenggong

(Shandong Industrial Ceramics Research and Design Institute Co., Ltd., Zibo 255000, Shandong, China)

Extended abstract:[Significance] In response to the rapid evolution of aerospace technologies, including deep space exploration and precision navigation for cruise vehicles, hypersonic and long-endurance aircraft have emerged as critical research frontiers. These advanced systems face extreme thermal challenges during operation, where combined effects of aerodynamic compression heating, frictional heat generation and thermal barrier effect can induce localized surface temperatures exceeding 1300 ℃ or even higher. Consequently, this thermal regime necessitates the urgent development of lightweight, high-temperature resistant insulation materials capable of maintaining structural integrity and functional performance, while preserving payload capacity. Such materials are critical to enabling the aircraft to operate reliably under extreme thermal conditions. Aerogels represent a class of nano-porous materials composed of aerogel particles, where the liquid component within the wet gel is substituted by air during the drying process, resulting in the formation of an interconnected solid network structure. Distinct from conventional thermal insulation materials, aerogels exhibit remarkable characteristics, such as ultra-low density (0.003–0.150 kg·m⁻³), exceptionally high specific surface area (500–1000 m2·g⁻¹) and extremely high porosity (95–99%). These properties, coupled with their nanoscale effects, render aerogels as unique "super thermal insulation materials", offering insulation efficiency that is 2–5 times superior to traditional thermal insulation materials. Consequently, aerogels have garnered significant attention and have a wide range of applications in energy, construction, aerospace and other fields. Currently, aerogels employed in high-temperature thermal protection primarily encompass oxide aerogels (such as SiO₂, Al₂O₃, ZrO₂ and binary or multi-oxide aerogels) and non-oxide aerogels (including carbon aerogels, carbide aerogels and nitride aerogels). This paper is aimed to provide a comprehensive analysis and summary of the preparation methods and properties of both oxide and non-oxide aerogels, aiming to establish a robust foundation for future research endeavors in the realm of thermal insulation materials, particularly in the fields of space exploration and aerospace engineering.[Progress] This paper is primarily to focus on the typical preparation methods and properties of oxide and non-oxide aerogels. Initially, the discussion centered on oxide aerogels, which encompass SiO₂ aerogel, Al₂O₃ aerogel, ZrO₂ aerogel, as well as binary and multi-oxide aerogels. The sol-gel reaction mechanisms and the temperature ranges applicable to several oxide aerogels are thoroughly analyzed. SiO₂ aerogel, notable for its long-term usability at temperatures between 600–800 ℃, stands out as one of the most remarkable aerogel insulation materials currently in terms of production volume. In comparison, Al₂O₃ aerogel exhibits enhanced temperature resistance, capable of withstanding temperatures exceeding 1000 ℃. The melting point of ZrO₂ can reach up to 2715 ℃, so ZrO₂ aerogel shows promising development prospects in the field of aerospace insulation. Furthermore, the paper delves into the details of binary and multi-oxide aerogels. In the context of SiO₂ aerogels, the introduction of heterogeneous elements, such as Y, Al, and Zr to partially replace Si, results in the formation of metal oxide-doped SiO₂ aerogels and non-silicate metal oxide aerogels. The incorporation of more stable metal elements bonded with oxygen in high-temperature environments significantly enhances the high-temperature stability of these composite aerogels. Similarly, in Al₂O₃ aerogels, the addition of elements like Si, La, and Ba leads to the creation of bicomponent and multi-component composite aerogels. These additions help inhibit atomic diffusion during heat treatment and prevent the crystal phase transition from γ-Al₂O₃ to α-Al₂O₃, thereby effectively improving the temperature resistance of the aerogel materials. In the case of ZrO₂ aerogels, the introduction of suitable impurity ions during preparation can form a replacement solid solution, increase oxygen vacancies and inhibit the formation and growth of crystal nuclei in ZrO₂ aerogels. This process aids in delaying phase transformation and stabilizing the crystal phase, further enhancing the material's properties. In the realm of non-oxide aerogels, this paper is intended to primarily explore carbon aerogel, carbide aerogel and nitride aerogel. Carbon aerogel, derived from the pyrolysis and carbonization of organic aerogels at high temperatures, emerges as an exceptional material for high-temperature insulation in oxygen-free environments. Remarkably, it maintains a robust mesoporous structure even at temperatures soaring to 2800 ℃. The influence of various factors, such as water content, catalyst content and pyrolysis carbonization temperature, on microstructure and properties of carbon aerogel, is reviewed, providing a comprehensive understanding of its performance for high-temperature applications. In the domain of carbide aerogel materials, the primary representatives include SiC aerogel, ZrC aerogel, SiOC aerogel, and ZrCO aerogel, among others. Notably, SiC aerogel exhibits remarkable temperature resistance, enduring temperatures as high as 1200–1500 ℃ in aerobic environments, marking it as a promising material for high-temperature applications. SiOC ceramics surpass SiC ceramics in oxidation and corrosion resistance at temperatures above 1400 ℃. ZrC, a quintessential transition metal carbide with a melting point reaching 3540 ℃, enables ZrC aerogel to withstand extreme temperatures exceeding 2000 ℃, making it ideal for high-speed cruising applications. The preparation methods of carbide aerogels are summarized, detailing the specific surface area, porosity, and thermal conductivity of carbide aerogels synthesized from precursors, such as RF/SiO₂, CF/SiO₂ and MTMS/DMDES. These insights contribute to a deeper understanding of the structural and thermal properties of carbide aerogels, paving the way for their optimized use in high-temperature environments. In the field of nitride aerogel materials, this paper primarily introduces Si₃N₄ aerogel and BN aerogel. BN aerogel can be synthesized using raw materials such as melamine diborate, boryazine and calcium phosphate. On the other hand, Si₃N₄ aerogel combines the outstanding properties of Si₃N₄ ceramics with the unique structural advantages of aerogels, which can be prepared through the pyrolysis and nitridation of RF/SiO₂ aerogel in N₂, or by incorporating precursors such as urea and melamine. Additionally, the mechanical strength, thermal conductivity, and porosity of the resulting Si₃N₄ aerogel are discussed, providing a detailed analysis of its performance characteristics. These insights underscore the potential of nitride aerogels for applications requiring exceptional thermal and mechanical properties.[Conclusions and prospects] The research progress of aerogel insulation materials applied in the field of aerospace is reviewed. In the domain of oxide aerogel insulation materials, the development of high-entropy ceramic aerogels with higher melting points, lower thermal conductivity and superior comprehensive performance represents a key direction for future advancements in thermal insulation materials. In the realm of non-oxide aerogel insulation materials, carbon aerogel exhibits limited antioxidant performance in aerobic environments. Although the formation of antioxidant coatings on the surface of carbon aerogel can enhance its oxidation resistance, the overall service life of the material remains constrained. Consequently, further improvements in its antioxidant properties are essential to expand its applicability and durability in high-temperature, oxygen-rich conditions.

Key words: aerogel; oxide aerogels; non-oxide aerogels; thermal insulation materials