Hierarchical Composite with Self-Adaptive Anisotropic Deformation for Thermal Protection System.

Rigid thermal protection materials such as ultra-high-temperature ceramics are desirable for applications in aerospace vehicles, but few materials can currently satisfy the emerging high-temperature sealing requirements for dynamic gaps created by the mismatch of the thermal expansion of different protection layers. Here, we design and fabricate a flexible biomimetic anisotropic deformation composite by multilayer cocuring onto fiber fabrics. It displays superior anisotropic deformation, whose longitudinal expansion ratio is 48 times greater than the transverse expansion ratio at specific temperatures. Furthermore, the ordered carbon structure created by transition-metal-catalyzed graphitization and the C/Si synergistic effect resulting from the combination of biomimetic fiber fabrics and SR enable the in situ formation of a high-temperature-resistant SiC crystalline phase within the char layer, ultimately resulting in exceptional thermal protection properties. By constructing hollow structures in situ, the back temperature of the composite, which is only 4.33 mm thick, is stabilized at 140 °C under the condition of continuous butane flame ablation (1300 °C) for 420 s. Multilayer structure and flexible features can facilitate large-scale preparation and arbitrary cutting and bending, adapted to different thermal protection areas.

In Situ Ceramization of Nanoscale Interface Enables Aerogel with Thermal Protection at 1950 °C.

Conventional carbon fiber felt-reinforced aerogel composites are often used as lightweight thermal protection systems (TPSs) for aerospace craft. However, due to their poor oxidation resistance, they have gradually failed to handle increasingly harsh thermal environments. In this work, a nanoscale composite coating interface of SiC-ZrC ceramic precursor is first constructed on the fiber surface. Subsequently, using the coated fiber felt as a three-dimensional skeleton and through polymerization-induced phase separation, an aerogel composite with excellent thermal protection in extreme thermal environments is prepared. Owing to the in situ ceramization of this nanoscale interface at ultrahigh temperatures, the back temperature of the 12 mm thick aerogel is only 147 °C after exposure to an oxyacetylene flame at 1950 °C for 70 s. Meanwhile, the central region of the aerogel recedes by only 7%. Not only does this work provide a way to enhance aerogels by constructing a self-ceramizable nanoscale interface it is also expected that the developed aerogel composite can be applied in the ultrahigh-temperature thermal protection of future aerospace craft.

Flexible Thermal Protection Polymeric Materials with Self-Sensing and Self-Adaptation Deformation Abilities.

Based on the strategy of killing two birds with one stone, we introduce thermally expandable microspheres into a silicone rubber matrix to fabricate temperature-responsive controllable deformation materials, which exhibit intelligent deformation properties as well as enhanced thermal protection performance, for dynamic thermal protection in the next-generation morphing aircrafts. The formation of hollow structures endows the material with intelligent thermal management ability and makes the thermal conductivity controllable, meeting the requirements of rapid deformation and excellent thermal insulation. The dimensions of the material adaptively expand with increasing temperature, and a constant 50N force can be provided to ensure reliable sealing. Moreover, benefiting from the synergistic effect of the hollow structure and zinc borate in the ceramization process of the silicone rubber, the 10 mm thick material can reduce the temperature from 2000 to 63 °C, and the mass ablation rate is only 4.8 mg/s. To broaden the application of our material, a sensor with a sandwich structure composed of different functional layers is designed. It is pleasantly surprising to observe that the sensor can provide real-time remote warning of fire and overheating sites with a response time as short as 1 s. This synergistic strategy opens a new possibility to fabricate intelligent thermal protection materials.

High residue bio-based structural-functional integration epoxy and intrinsic flame retardant mechanism study.

Research on structural-functional integration of polymers has become an inevitable trend and development orientation in modern materials science. An intrinsic flame-retardant epoxy with superior mechanical properties and reusability is of great application value as a composite matrix and structural material. We newly synthesized two bio-based epoxy resins, VSE and VDE, the Young's modulus of product cured by DDM (4,4-diaminodiphenyl methane) achieve 5013 MPa and 4869 MPa, respectively. The LOI values of VSE and VDE were 38.7% and 34.5% respectively and both meet UL-94 V-0 rating. High char residue at 800 °C (34.5% and 28.0%, respectively) means a superior thermal stability which conventional epoxies are unreachable. Besides, cured VDE have convenient processability which can be re-shape as heating up and retain complete structural performance after cooling to room temperature. Furthermore, thermogravimetric analysis coupled with infrared spectroscopy (TGA-IR) and energy dispersive X-ray spectroscopy (EDS) were used to assist scanning electron microscopy (SEM) to investigate the intrinsic flame-retardant mechanism. In this work, the effect and process of nitrogen-phosphorus synergy on flame retardant is revealed finally. These results indicate the newly prepared epoxy has excellent flame retardancy, mechanical properties and recyclability which opens new possibilities in practical applications of epoxy such as coatings, potting or composite matrix in the near future.