The role of nanofiber thermal insulation materials in the aerospace field

Aerospace aircraft need to withstand aerodynamic heating for a long time during flight, and the surface of the substrate will generate high temperature. In order to ensure the safety of the aircraft's main structure and internal instruments and equipment, high-efficiency insulation materials must be used to prevent external heat from spreading to the interior. At the same time, the lightweight and efficient thermal insulation protection system is of great significance for reducing the load of the aircraft and extending the flight distance. Nanofiber material has the advantages of small pore size and high porosity, and is an ideal lightweight and efficient heat insulation material. This article mainly introduces the latest research progress of current two-dimensional nanofiber membranes and three-dimensional nanofiber aerogel thermal insulation materials. Two-dimensional nanofiber membrane thermal insulation materials: materials with small thickness but excellent thermal insulation performance are required for small spaces such as missile battery thermal insulation sleeves and engines. Due to the small fiber diameter, the stacking thickness of two-dimensional nanofiber membrane materials is controllable (generally less than 100μm) ), high porosity and other advantages can be used for heat insulation in narrow spaces. Nanofiber membrane thermal insulation materials can be divided into polymer nanofiber membranes, carbon nanofiber membranes and ceramic nanofiber membranes according to their composition. Macromolecule nanofibers, such as polyvinylidene fluoride (PVDF) nanofiber membranes, have higher porosity and tortuous mesh channels, so that the transmission path of air molecules inside the material becomes longer, and heat is lost during the propagation process. , Thus reducing the thermal conductivity of the material. In order to further reduce the thermal conductivity of the material, some scholars have coated the surface of PVDF nanofibers with SiO2 nanoparticles through impregnation modification technology to further reduce the pore size of the fiber membrane and reduce heat convection. However, the structure of this material is easily damaged in a high-temperature environment, and it is difficult to meet application requirements. Carbon nanofibers have the advantages of large specific surface area, high porosity, good chemical stability, high specific strength, etc., and have broad application prospects in the fields of electronics, energy, aerospace, etc. As the degree of graphitization increases, carbon nanofiber membrane materials have gradually improved high temperature resistance, but their thermal insulation performance will also be greatly reduced, so it is difficult to meet the demand for simultaneous improvement of high temperature resistance and thermal insulation performance. Ceramic materials have the advantages of high temperature resistance, corrosion resistance, good insulation, etc., and have a wide range of applications in high temperature insulation, sound absorption, catalysis and other fields. However, most of the existing ceramic nanofibers have defects such as high brittleness, poor mechanical properties, and inability to resist bending, which limit their practical use. In order to overcome this shortcoming, some scholars have prepared SiO2 nanofiber membranes with amorphous structure and good flexibility by adjusting the properties of the spinning solution and process parameters. At the same time, it is also possible to introduce SiO2 aerogel nanoparticles between the fibers through the impregnation modification method to construct a SiO2 nanoparticle/nanofiber composite material to improve the thermal insulation performance of the SiO2 nanofiber membrane. Three-dimensional nanofiber aerogel thermal insulation material: Although two-dimensional nanofiber has good thermal insulation properties, it is difficult to achieve an effective increase in the thickness direction (> 1 cm), which severely limits its use in high-power engine thermal insulation and cabin insulation. Application in the fields of fire protection and heat insulation of walls. Compared with two-dimensional nanofiber membranes, three-dimensional nanofiber aerogel materials have the advantages of controllable size, high porosity, and high degree of pore tortuosity, so they have broad application prospects in the fields of heat insulation, warmth, and sound absorption. At present, common nanofiber aerogel thermal insulation materials mainly include polymer nanofiber aerogel and ceramic nanofiber aerogel. Ceramic nanofiber aerogel: Ceramic aerogel material has excellent high temperature resistance, corrosion resistance and thermal insulation properties, and is one of the main materials for thermal protection of aerospace vehicles. The aerogel heat insulation materials currently used are mainly ceramic fiber reinforced SiO2 nanoparticle aerogels. Due to the weak interaction between the nanoparticles and the ceramic fibers, the nanoparticles are easy to fall off during the use of the material, which makes the structure of the material stable. The performance and thermal insulation performance are greatly reduced. In order to solve the above-mentioned problems, some scholars used flexible ceramic nanofibers as the construction element and used the original three-dimensional fiber network reconstruction method to construct ultra-lightweight and super-elastic ceramic nanofiber aerogel materials. The aerogel material has a honeycomb-like mesh structure, and the fibers in each mesh are entangled and bonded to each other to form a stable fiber network, which gives the aerogel good structural stability. It can still rebound quickly under compression with large deformation (80% strain), and its plastic deformation is only 12% after 500 compression cycles, which is better than existing ceramic aerogel materials. At the same time, the material can recover after 50% compression under the flame of alcohol lamp (about 600℃) and butane blowtorch (about 1100℃), showing excellent high-temperature compression and resilience performance. Macromolecular nanofiber aerogels: address the problems of poor mechanical properties and high brittleness of existing aerogel materials. Some scholars used cellulose nanocrystals with high elastic modulus, high strength, and low density as the construction element, and prepared cellulose nanocrystal aerogels with good transparency and mechanical properties through gel and supercritical drying methods. It can be bent to 180° without damage, and it can still recover after compression under large deformation (80%) and the maximum stress is greater than 200 kPa. In addition, cellulose nanocrystals also exhibit excellent thermal insulation properties.

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