Ceramicization mechanism and thermal insulation/ablative properties of hollow microspheres/boron phenolic composites

Phenolic resins with excellent ablative properties and thermal insulation are required in aerospace technology. However, the composites suffer from pyrolytic carbonaceous residues, resulting in susceptible erosion and peeling. This work provides a novel phenolic resin composite with high thermal insulation capacity by introducing hollow silica microspheres (HSMs) as an insulation layer. The effect of HSMs content on the ablation behavior of the composites was investigated, and the ablation mechanism was elucidated. The results show that the composites with microspheres exhibit high uniformity and improved bending strength. By introducing microspheres, the fiber distribution is uniform, resulting in an increase of the bending strength after static ablation to be 7.4 MPa, which is 87% higher than the matrix. The thermal stability of the composite is improved simultaneously and the ablation residual rate after static ablation increases from 67% to 73%. When oxyacetylene ablation for 20 s at the oxygen and acetylene flow rates of 1145 L/h and 838 L/h, respectively, the microspheres construct an insulating network, and the back surface temperature decreases from 280 °C to 178 °C.