Nano-porous aluminium oxide thermal insulation materials primarily encompass aluminium oxide aerogel insulation and nano-alumina pressed insulation. These materials have broad application prospects in industrial and aerospace sectors due to their low density, low thermal conductivity, and high-temperature resistance. Alumina aerogel thermal insulation materials are presently manufactured primarily via sol-gel synthesis coupled with drying techniques. The existing work focuses on optimizing precursor synthesis, drying methods, and reinforcing agent/shading agent composites. Conversely, nano-alumina pressed thermal insulation materials are predominantly produced by dry and wet forming processes. The research emphasis lies in maintaining low material density, while enhancing thermal conductivity, high-temperature resistance, and mechanical properties. This review represents research progress on the preparation techniques and performance enhancement of nanoporous alumina thermal insulation materials, analyzes the existing challenges, and outlines future research directions.

Nano-porous alumina thermal insulation materials have a significant application value in cutting-edge fields such as aerospace due to their lightweight properties, low thermal conductivity, and excellent high-temperature stability. This review primarily represents research progress on the preparation techniques and performance enhancement of nanoporous alumina thermal insulation materials for the past five years. Regarding alumina aerogel insulation materials, several challenges remain although extensive studies are conducted on precursor selection, sol-gel process refinement, drying method optimisation, and reinforcement composite development. These primarily include complex fabrication processes, high costs, safety concerns (associated with reactor usage), lengthy preparation cycles, and the inability to achieve continuous production. To address these issues, a subsequent research should focus on process optimisation and functional design. This includes developing novel precursors and refining drying techniques.

1) Enhancing sol-gel processes can strengthen wet gel structures, thereby reducing replacement and ageing times;

2) Exploring low-cost aluminium salts as precursors;

3) Eliminating high-pressure autoclaves for drying to lower equipment costs and energy consumption.

The existing literature on nano-alumina pressed thermal insulation materials remains relatively scarce. Their forming methods primarily comprise dry forming and wet forming. Dry forming relies on mechanical bonding forces between alumina powder particles, achieving a physical bonding through compression to connect particles into composite materials. However, this method exhibits low material reliability and inadequate mechanical properties, rendering it unsuitable for practical applications. In contrast, wet forming uses physical or chemical means to regulate particle distribution and bonding patterns. It utilizes liquid-phase media to disperse, align, and structurally stabilise nano-alumina particles, ultimately forming green bodies or materials with specific morphologies. Although this method yields aluminium oxide thermal insulation composites with a favorable formability, it still has some challenges like high density, complex processing, and susceptibility to cracking during liquid-phase media removal. Although post-processing techniques (such as sol-impregnation or high-temperature heat treatment) can be applied to nano-alumina pressed insulation green bodies, the thermal conductivity of the treated insulation materials increases significantly, making them unsuitable for many applications. To achieve both enhanced mechanical properties and low thermal conductivity in insulation composites, a future research needs to focus on curing the interfaces between nanoparticles to improve the material mechanical performance.