Hierarchical-design coating on C/C composite with excellent combination of autonomously self-healing ability and low oxygen permeability from 973 K to 1273 K

Antioxidant SiO 2 coating exhibits low cost and great compatibility with existing uses, but is strongly limited by its poor fluidity and high oxygen permeability from 973 K to 1273 K. Therefore, the hierarchical-design Glass/MoSi 2 -B 2 O 3 @SiO 2 -SiC coating was fabricated on C/C composite by a simple embedding method, and followed by a hot dip process. This composite yielded excellent combination of long-term antioxidant abilities and thermal shock resistances. As oxidized at 973 K for 1500 h, its mass loss was 0.35 %, and only 0.66 % at 1073 K for 2600 h. After thermal shocks 270 times, the weight loss was only 0.56 %. Interestingly, the Glass/MoSi 2 coating acted as a self-healing encapsulation shelter against oxygen, whilst the B 2 O 3 @SiO 2 layer yielded stable healing effect. The B 2 O 3 @SiO 2 microcapsule facilitated the activation of B 2 O 3 , SiO 2 phases, and borosilicate glass sequentially as temperature rose, leveraging their unique advantages in defect healing. Through the synergistic effects of interface encapsulation and defect self-healing, the oxygen kept osmotic diffusion. This study underscores the significance of hierarchical designs in coatings, facilitating structure optimizations and enhancing antioxidant capabilities at multiple levels.