Ultralight, thermally insulating, and temperature-resistant inorganic aerogels, including particulate and fibrous aerogels, serve as excellent thermal protection materials and hold significant applications in aerospace, energy, and environmental engineering. In this work, hierarchical aluminum borate whisker (ABOw) aerogels were prepared via a sol–gel process, followed by freeze-drying and high-temperature in-situ reaction, in which ABOw uniformly grows within the matrix, interspersed with either mullite fibers covered by ABOw or rod-like ABOw assemblies. The size of ABOw within the matrix and the phase transformation temperature (Al₄B₂O₉ → Al₁₈B₄O₃₃) decrease with increasing Al/B ratio. ABOw growth follows the V–S–L mechanism: Within the matrix, whiskers nucleate uniformly around alumina particles and then grow; in contrast, whiskers on the fiber surface nucleate heterogeneously on preferentially oriented mullite grains, grow in clusters, and gradually merge into a single whisker of increasing length. The density of the ABOw aerogel ranges from 0.173 to 0.243 g/cm³, which decreases with increasing calcination temperature and decreasing Al/B ratio. The thermal conductivity lies between 0.0560 and 0.0873 W/(m·K) and increases with increasing calcination temperature. The ABOw aerogels calcined at 1200 °C have a compressive strength of 97.8–214.3 kPa, and the main failure modes are matrix fracture and interfacial cracking. The aerogel with an Al/B ratio of 2 : 1 exhibits a linear shrinkage of less than 5% without obvious welding phenomena after high-temperature heat treatment (1400 °C/20 h, 1500 °C/2 h). This high-temperature resistant, lightweight, and thermally insulating ABOw aerogel is an excellent thermal protection material and is also suitable for high-temperature filtration, adsorption, and catalysis.

A novel porous mullite ceramic with overlapping and interlocking mullite whiskers was prepared using in-situ whisker growth technology. Without the use of any pore-foaming agents, the formation of a porous structure was facilitated by the atomic rearrangement of Al₂O₃ and SiO₂ catalyzed with MoO₃. The effects of the molar ratio of Al₂O₃ to SiO₂, MoO₃ content, sintering time, and sintering temperature on the structure and properties of (xAl₂O₃·ySiO₂)_m(MoO₃)_n-T-t (T = sintering temperature, and t = sintering duration) ceramics were comprehensively studied. The molar ratio of Al₂O₃ to SiO₂ had a more significant effect on the morphology of the whiskers, while the other three conditions generally promote whisker growth. Under conditions of x : y = 3 : 1.8, m : n = 9 : 1, T = 1300 °C, and t = 3 h, (3Al₂O₃·1.8SiO₂)₉(MoO₃)₁-1300 °C-3 h ceramics exhibited a satisfactory compressive strength of 4.81 MPa at a density of 0.76 g/cm³. Microstructural analysis revealed that a multi-level reinforcement structure was obtained by the interlaced distribution of tiny and large whiskers, significantly increasing the crack deflection area and enhancing the crack deflection resistance when resisting external forces. After 100 thermal shock cycles between room temperature and 1300 °C, the compressive strength retention rate was 77.13%. In addition, the multi-scale whisker-overlapping structure also has a high specific surface area (1.83 m²/g), high porosity (74.18%), and small pore size (7.44 μm). The thermal conductivity was as low as 0.260 W/(m·K), and the ceramic maintained a rear-side temperature below 200 °C when subjected to a 1300 °C butane flame. In addition, the regulatory mechanism between parameters, structure, and properties was analyzed in detail, providing data support for research on porous materials.

High-temperature-resistant adhesives are critical materials in the aerospace field. The zirconium-modified aluminum phosphate-based adhesives developed in this work had the advantage of adjustable thermal expansibility, achieving a high matching of coefficient of thermal expansion (CTE) with alumina. The introduction of zirconium can significantly improve the thermal stability of the adhesive matrix, and the Zr/Al ratio substantially affects the various reaction processes inside the adhesive, especially the types of zirconium-containing compounds. Most of the zirconium-containing compounds in the A7Z3 adhesive were ZrO₂ only when the mass ratio of zirconium hydroxide to aluminum hydroxide was 3 : 7, which was the key reason why it had the highest CTE. The room-temperature bonding strength of A7Z3 after heat treatment at 1500 °C reached 67.2 MPa. After pretreatment at 1500 °C, the high-temperature bonding strength of A7Z3 was greater than 50 MPa in the range of (room temperature) RT–1000 °C. After 40 thermal cycles between RT and 1500 °C, the bonding strength still reached 10 MPa. Physical bonding occurred at temperatures below 1000 °C, while chemical bonding dominated above 1000 °C based on the generation of Al₅BO₉ and mullite at the interfaces.