Lightweight nitrogen‐doped phenolic composites with enhanced thermal ablation‐insulation performance by improving pyrolysis gas blocking effect

Abstract

Lightweight phenolic ablative composites are considered to be the most reliable materials for thermal protection systems. However, improving the thermal ablation‐insulation performance of heritage phenolic aerogel‐based ablators for extremely complex environments is still necessary. Herein, from the perspective of enhancing the gas‐blocking effect, we design and fabricate a series of needle quartz fiber‐reinforced melamine‐phenolic aerogels (NQF/MPAs) composites by polycondensation of melamine and phenolic in a sol–gel process, followed by ambient drying. The effects of melamine content on the comprehensive performance are analyzed. The prepared nitrogen‐doped phenolic aerogel composites exhibit low density of 440–490 kg/m3, high tensile strength of 36.3–39.1 MPa, and low thermal conductivity of 0.041–0.043 W/(m·K) at room temperature. Simultaneously, the modified composite exhibits excellent high‐temperature insulation property with lower equivalent thermal conductivity of 0.045 W/(m·K) at 1000°C. In arc wind tunnel testing of 130 kW/m2 for 1000 s, the linear recession rates of the composites show a great improvement from 3.7 × 10−6 to 2.5 × 10−6 m/s with the proper introduction of melamine. Furthermore, a one‐dimensional finite element model is stablished, which indicate the introduction of melamine can significantly improve the mass flow rate of pyrolysis gas and the corresponding block factor is enhanced from 0.958 to 0.848.Highlights Economic sol–gel method and ambient drying for composites production. Phenolic aerogel‐based ablative composite with enhanced gas blocking effect. The pyrolysis gas blocking effect is controllable with melamine content. Combined experimental‐simulation approach for ablators designing.