Novel hierarchically structured aluminum borate whisker aerogel via sol-gel method and in-situ reaction for high-temperature thermal protection

With the rapid development of hypersonic aircraft and aerospace equipment, as well as the technological upgrading in the field of industrial high-temperature thermal protection, the demand for high-temperature thermal insulation materials keeps rising. Inorganic aerogels, featuring ultra-low density, excellent thermal insulation and high-temperature resistance, have become key materials to address thermal protection challenges in multiple fields.

Among inorganic aerogels, particulate aerogels are composed of nanoscale particles and mainly prepared via a sol-gel method, but they are highly brittle and fragile. While fibrous aerogels form a three-dimensional network interwoven by nanoceramic fibers, with outstanding flexibility and toughness, yet their preparation process is relatively complex. The nanostructural units of aerogels fundamentally determine material properties, so constructing aerogels with novel nanoscale units is of great research significance. Aluminum borate ceramics have high strength, high modulus, excellent high-temperature resistance and corrosion resistance. Their orthorhombic crystal structure shows remarkable anisotropy and tends to form whiskers, and the whisker morphology can be precisely controlled by adjusting the Al/B ratio of raw materials and the heat treatment temperature. The development of aluminum borate whisker aerogels based on this is expected to break through the performance limitations of traditional aerogels and provide new approaches for the research of novel high-temperature thermal protection materials.

Recently, a team of material researchers led by Mingchao Wang from Civil Aviation University of China, China reported a novel hierarchically structured aluminum borate whisker aerogel via sol-gel method and in-situ reaction for high-temperature thermal protection. This work systematically investigated the effects of firing temperature and Al/B ratio on the structure and properties of the aerogels, clarified the whisker growth mechanisms at different sites and the formation process of hierarchical porous structures, and characterized the mechanical, thermal protection and temperature resistance performances of the material, providing a new strategy for high-temperature thermal protection.

The team published their work in Journal of Advanced Ceramics on February 21, 2026.

“In this study, hierarchically structured aluminum borate whisker (ABOw) aerogels were prepared via the sol-gel method, freeze-drying and high-temperature in-situ reaction. The gelation process of boron-aluminum sol was regulated by introducing aluminum sols with different activities, and the strength of the gel network was enhanced by adding chopped mullite fibers. In the as-prepared aerogels, uniformly distributed aluminum borate whiskers acted as the matrix, while mullite fibers fully covered with ABOw or rod-like ABOw assemblies were interspersed in the matrix, forming a hierarchical porous structure.” said Wang.

“This work systematically investigated the growth process of aluminum borate whiskers both in the matrix and on the surface of mullite fibers. Significant differences in the growth processes at the two positions were revealed, and the corresponding growth mechanisms were clarified: ABOw in the matrix nucleated and grew uniformly around alumina particles, while those on the fiber surface nucleated heterogeneously on preferentially oriented mullite grains, grew in clusters and gradually merged into longer whiskers.” said Wang.

“The aluminum borate whisker aerogels possess a service temperature exceeding 1400℃, low density, low thermal conductivity and high compressive strength. The Al/B ratio and heat treatment temperature exert significant effects on the whisker morphology, pore structure and performance of the material. The sample with an Al/B ratio of 1:2 shows a linear shrinkage of less than 5% after heat treatment at 1400 ℃ for 20 h and 1500℃ for 2 h. Its outstanding high-temperature resistance gives it distinct advantages in high-temperature thermal protection applications.” said Wang.

Other contributors include Xin Tao, Liangying Tang, Yuqi Zhao, Fangyu Zhao, Ziwei Xiang, Xinyue He from Civil Aviation University of China, China.

About Author

Mingchao Wang is an Associate Professor and Master’s Supervisor at the Civil Aviation University of China, a member of the 7th China Association of Young Scientists and Technologists, and a Tier-3 Talent of Tianjin “131” Innovative Talent Training Program. He has long been engaged in the research and development of high-temperature resistant adhesives, bonding theory, flame-retardant and thermal-insulating coatings, and surface engineering. Having presided over and participated in more than 10 scientific research projects at national, provincial, ministerial and other levels, he has published over 50 SCI papers as the first author and corresponding author in internationally renowned journals.

Funding

This work is supported by the Fundamental Research Funds for the Central Universities (Project No. 3122025036).

About Journal of Advanced Ceramics

Journal of Advanced Ceramics (JAC) is an international academic journal that presents the state-of-the-art results of theoretical and experimental studies on the processing, structure, and properties of advanced ceramics and ceramic-based composites. JAC is Fully Open Access, monthly published by Tsinghua University Press, and exclusively available via SciOpen. JAC’s 2024 IF is 16.6, ranking in Top 1 (1/34, Q1) among all journals in “Materials Science, Ceramics” category, and its 2024 CiteScore is 25.9 (5/130) in Scopus database. ResearchGate homepage: https://www.researchgate.net/journal/Journal-of-Advanced-Ceramics-2227-8508