Nanofiber Insulation Materials: There Are Bright Prospects In Aviation And Aerospace.

Aeronautics and Astronautics are subjected to prolonged aerodynamic heating during flight. The surface of the spacecraft will generate high temperatures. In order to ensure the safety of the main structure and internal equipment of the aircraft, efficient insulation materials must be used to prevent the external heat flux from spreading to the interior.

At the same time, lightweight and efficient insulation protection system is of great significance for reducing the load of aircraft and prolonging the distance of flight.

Nanofiber has the advantages of small pore size and high porosity. It is an ideal lightweight and efficient thermal insulation material.

This paper mainly introduces the latest research progress of two dimensional nanofiber membrane and three dimensional nanofiber aerogel insulation materials.

Two dimensional nanofiber membrane insulation material

The narrow space for missile batteries, such as thermal insulation sleeve and engine, requires materials with relatively small thickness but excellent thermal insulation properties. Two dimensional nanofiber membrane materials can be used for heat insulation in narrow space because of their small fiber diameter, controllable thickness (generally less than 100 m) and high porosity.

Nanofiber membrane insulation materials can be divided into polymer nanofiber membrane, carbon nanofiber membrane and ceramic nanofiber membrane according to their composition.

Polymer nanofibers, such as polyvinylidene fluoride (PVDF) nanofiber membrane, have higher porosity and tortuous meshes, thus making the pport path of air molecules in the material longer and the heat loss in the propagation process, thus reducing the thermal conductivity of the material.

In order to further reduce the thermal conductivity of materials, some scholars have coated SiO2 nanoparticles on the surface of PVDF nanofibers by impregnation modification technology, which further reduces the pore size and reduces heat convection.

However, the structure of the material is easily destroyed in high temperature environment, so it is difficult to meet the application requirements.

Carbon nanofibers have the advantages of large specific surface area, high porosity, good chemical stability and high specific strength. They have wide application prospects in the fields of electronics, energy, aerospace and so on.

With the increase of graphitization degree, carbon nanofiber membrane materials will gradually enhance their high temperature resistance. However, their thermal insulation properties will also decrease significantly. Therefore, it is difficult to meet the requirements of simultaneous improvement of heat resistance and insulation performance.

Ceramic materials have the advantages of high temperature resistance, corrosion resistance, good insulation and so on. It is widely used in the fields of heat insulation, sound absorption, catalysis and other fields.

However, most of the existing ceramic nanofibers have the defects of high brittleness, poor mechanical properties and no bending resistance, which limits their practical use.

In order to overcome this shortcoming, a SiO2 nanofiber membrane with amorphous structure and good flexibility has been prepared by adjusting the properties and technological parameters of spinning solution.

At the same time, SiO2 aerogel nanoparticles can be introduced into the fibers by impregnation modification, and SiO2 nanoparticles / nanofiber composite materials can be constructed to enhance the thermal insulation properties of SiO2 nanofiber films.

Three dimensional nanofiber aerogel insulation material

Although the two-dimensional nanofibers have good thermal insulation performance, it is difficult to achieve an effective increase in thickness direction (> 1 cm), which severely limits its application in high-power engine insulation, bulkhead fire protection and heat insulation.

Compared with two-dimensional nanofiber membrane, 3D nanofiber aerogel has the advantages of controllable size, high porosity and high degree of pore twists. Therefore, it has broad application prospects in thermal insulation, thermal insulation, sound absorption and other fields.

At present, the common nanofiber aerogel insulation materials include two kinds of polymer nanofiber aerogels and ceramic nanofibers aerogels.

Ceramic nanofibers aerogels

Ceramic aerogels have excellent properties of high temperature resistance, corrosion resistance and heat insulation. They are one of the main materials for aerospace vehicle thermal protection.

The aerogel insulation materials are mainly ceramic fiber reinforced SiO2 nanoparticle aerogels. Due to the weak interaction between nanoparticles and ceramic fibers, nanoparticles are easy to fall off during the use of materials, resulting in a significant decrease in structural stability and thermal insulation properties of materials.

In order to solve the above problems, some scholars used flexible ceramic nanofibers as the building blocks, and constructed the ultra lightweight and super elastic ceramic nanofibers aerogels by using the original 3D fiber network reconstruction method.

Schematic diagram of preparation process of ceramic nanofibers aerogels

The aerogel material has honeycomb like mesh structure, and each mesh is intertwined and bonded to form a stable fiber network, giving the aerogels good structural stability.

It can still rebound rapidly under large strain (80% strain) compression. After 500 cycles of compression, the plastic deformation is only 12%, which is superior to the existing ceramic aerogel material.

At the same time, the material can still be recovered after compressing 50% at the alcohol lamp flame (about 600 degrees centigrade) and butane burner (about 1100 degrees Celsius), showing excellent compression and resilience at high temperature.

Compression of ceramic nanofiber aerogels under alcohol lamp

Compression of ceramic nanofiber aerogels under butane burner flame

Photos of petals with different petals at 10 min after 350 degree heat stand.

Polymer nanofibers aerogels

The existing aerogels have poor mechanical properties and large brittleness.

Some scholars have used cellulose nanocrystals with high elastic modulus, high strength and low density as the building blocks, and prepared cellulose nanocrystalline aerogels with good pparency and mechanical properties by gel and supercritical drying. They can be bent to 180 degrees without damage. At the same time, they 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.