Alpha Al₂O₃ Nanosheet-Based Biphasic Aerogels with High-Temperature Resistance up to 1600 °C

Abstract

Alumina aerogels are desirable for lightweight and highly efficient thermal insulation. However, they are typically constrained by brittleness and structural collapse at high temperatures. The manufacture of alumina aerogels with ultralow thermal conductivity and excellent thermal stability at high temperatures beyond 1300 °C is still challenging. Herein, alumina aerogels with superior ultrahigh-temperature-resistant and thermal insulation were successfully prepared by assembling the α-Al2O3 nanosheets with silica sols as the high-temperature binders. Benefiting from the generation of the mullite-covered alumina biphasic structure, the α-Al2O3 nanosheet-based aerogels (ANSAs) exhibit excellent thermal and chemical stabilities even after calcination at as high as 1600 °C. The ANSAs had a low thermal conductivity (0.029 W·m–1·K–1 at room temperature), structural stability with a measured compressive strength of 0.6 MPa, and good thermal shock resistance. Furthermore, the 2D α-alumina@mullite core–shell sheets were also prepared as assembly units to construct aerogels (AMSAs). This core–shell structure can improve temperature resistance through inter-lattice suppression under continuous energy input at high temperatures. The AMSAs have a linear shrinkage of only 2.7% after calcination at 1600 °C for 30 min, further improving the temperature resistance, making them an ideal super-insulating material for applications at extremely high temperatures.

Revealing Disparities in Porous Networks Between Yttria Aerogel Assemblies with Nanosheets and Nanoparticles and Their Ultrathermal Insulation and Optical Properties

“…In contrast, the nanosheet-Y 2 O 3 aerogel exhibits a more hierarchical pore distribution, allowing for the dissipation of the sintering stress. Consequently, the presence of these pores mitigates the extent of shrinkage during high-temperature assessment . This is explored in more detail in the Supporting Information (Figure S11).…”

“…Consequently, the presence of these pores mitigates the extent of shrinkage during high-temperature assessment. 12 This is explored in more detail in the Supporting Information (Figure S11).…”

“…9,10 Recent advancements have introduced anisotropic structures, specifically 2D nanosheets, 11 into aerogels, resulting in distinctive morphologies and exceptional mechanical, thermal, and optical properties. 12 These nanosheets exhibit tunable, size-dependent physical and chemical properties that are not achievable with isotropic nanoparticles. 13,14 The sol-gel process enables irregular packing of anisotropic nanosheet building blocks, leading to more complex porous networks; however, the exploration of these unique pore collections which are different from those formed by nanoparticle assemblies and the resultant distinct properties remains limited.…”

“…Nanoporous aerogels have garnered significant attention due to their remarkable properties, including ultralow density, high porosity, and substantial specific surface area. − These attributes have led to their utilization in various fields such as thermal insulation, catalysis, energy storage, and conversion. − The fundamentality of these applications lies in the continuous solid skeleton that percolates throughout the three-dimensional space, creating a tortuous porous network. Generally, the skeleton consists of interconnected nanoparticles resembling a pearl-necklace architecture. , Recent advancements have introduced anisotropic structures, specifically 2D nanosheets, into aerogels, resulting in distinctive morphologies and exceptional mechanical, thermal, and optical properties . These nanosheets exhibit tunable, size-dependent physical and chemical properties that are not achievable with isotropic nanoparticles. , The sol-gel process enables irregular packing of anisotropic nanosheet building blocks, leading to more complex porous networks; however, the exploration of these unique pore collections which are different from those formed by nanoparticle assemblies and the resultant distinct properties remains limited.…”

Mullite Nanosheet/Titania Nanorod/Silica Composite Aerogels for High-Temperature Thermal Insulation

“…Composite oxides appear to have better sintering resistance, like mullite and MgAl 2 O 4 . Therefore, our previous work designing the α-alumina@mullite core–shell structure to construct alumina-based aerogels can provide well-improved temperature resistance, with a linear shrinkage of only 2.7% up to 1600 °C . Mullite is a member of the stable performance compound in the alumina-silica system with a melting point of up to 1850 °C and good thermal stability under high-temperature oxygen-containing conditions without polycrystalline transition. − Moreover, mullite has excellent high-temperature creep resistance due to its difficulty in silicon–aluminum ion diffusion and lattice dislocation slip resistance .…”