The role of nanofiber thermal insulation materials in aerospace

Aerospace aircraft needs 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 main structure of the aircraft and the safety of internal instruments and equipment, high-efficiency thermal insulation materials must be used to prevent external heat flow from diffusing to the interior. At the same time, the lightweight and efficient thermal insulation protection system is of great significance for reducing the aircraft load and extending the flight distance. Nanofiber material has the advantages of small pore size and high porosity, and is an ideal lightweight and efficient thermal insulation material. This paper mainly introduces the latest research progress of two-dimensional nanofiber membranes and three-dimensional nanofiber aerogel thermal insulation materials. Two-dimensional nanofiber membrane thermal insulation material: Small spaces such as missile battery heat shields and engines require materials with small thickness but excellent thermal insulation performance. Two-dimensional nanofiber membrane materials have a small fiber diameter and a controllable stacking thickness (generally less than 100μm), the advantages of high porosity can be used for thermal insulation in small spaces. Nanofiber membrane insulation materials can be divided into polymer nanofiber membranes, carbon nanofiber membranes and ceramic nanofiber membranes according to their composition. Polymer 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 is longer, and heat is lost during propagation. , thus reducing the thermal conductivity of the material. In order to further reduce the thermal conductivity of the material, some scholars have coated SiO2 nanoparticles on the surface of PVDF nanofibers by impregnation modification technology to further reduce the pore size of the fiber membrane and reduce thermal convection. However, the structure of this material is easily damaged in a high temperature environment, making it difficult to meet application requirements. Carbon nanofibers have the advantages of large specific surface area, high porosity, good chemical stability, and high specific strength, and have broad application prospects in electronics, energy, aerospace and other fields. With the increase of the degree of graphitization, the high temperature resistance of carbon nanofiber membrane materials will gradually improve, but its thermal insulation performance will also be greatly reduced, so it is difficult to meet the needs of 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 heat 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 bend, 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 and process parameters of the spinning solution. At the same time, SiO2 aerogel nanoparticles can also be introduced between fibers by impregnation modification method to construct SiO2 nanoparticle/nanofiber composite materials, and improve the thermal insulation performance of SiO2 nanofiber membrane. Three-dimensional nanofiber aerogel thermal insulation material: Although two-dimensional nanofibers have good thermal insulation properties, it is difficult to achieve an effective increase in the thickness direction (> 1 cm), which seriously limits their use in high-power engine thermal insulation, cabin insulation, etc. Application in the field of wall fire protection and heat insulation. Compared with two-dimensional nanofibrous membranes, three-dimensional nanofibrous 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, heat preservation, and sound absorption. At present, the common nanofiber aerogel 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 currently used aerogel insulation materials are mainly SiO2 nanoparticle aerogels reinforced by ceramic fibers. 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, so that the structure of the material is stable. The performance and thermal insulation performance are greatly reduced. In order to solve the above problems, some scholars have used flexible ceramic nanofibers as building blocks, and used an original three-dimensional fiber network reconstruction method to construct ultra-light and super-elastic ceramic nanofiber aerogel materials. The aerogel material has a honeycomb-like mesh structure, and fibers in each mesh are entangled and bonded to each other to form a stable fiber network, which endows the aerogel with good structural stability. It can still rebound rapidly under large deformation (80% strain) compression, and its plastic deformation is only 12% after 500 compression cycles, which is superior to the existing ceramic aerogel materials. At the same time, the material can still recover after being compressed by 50% under the flame of an alcohol lamp (about 600 °C) and a butane torch (about 1100 °C), showing excellent high-temperature compression resilience. Polymer nanofiber aerogel: Aiming at 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 building blocks, and prepared cellulose nanocrystal aerogels with good transparency and mechanical properties by gel and supercritical drying methods. bendable to 180°Without failure, it can still recover after compression under large deformation (80%) and the maximum stress is greater than 200 kPa. In addition, cellulose nanocrystals also exhibited excellent thermal insulation properties.
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