Dynamic Multi‐Stage Ceramization and Covalent Interfacial Coupling in SiZrB Precursor‐Enhanced EPDM Composites for Ablation Resistance

ABSTRACT Developing advanced thermal protection systems (TPS) for space applications requires elastomeric composites that combine mechanical strength with ablation resistance. This study proposes a synergistic modification strategy based on covalent interfacial coupling and dynamic multistage ceramization. An organic–inorganic hybrid SiZrB precursor was designed to reinforce ethylene‐propylene‐diene monomer (EPDM) rubber. Within the EPDM vulcanization network, the SiZrB precursor acted as a multisite cross‐linking node that converted weak physical interactions into covalent linkages. The EPDM/SiZrB/3:1 composite exhibited a tensile strength of 8.29 MPa, representing a 43.9% increase relative to the EPDM/SiO 2 reference. Furthermore, the resulting interface, formed through double‐bond cross‐linking, significantly reduced the phonon mean free path through anharmonic scattering, thereby lowering the thermal conductivity to 0.242 W/(m·K). Under extreme oxy‐acetylene ablation conditions, the composite exhibited an adaptive heat‐shielding mechanism. During the initial ablation stages, the formation of low‐melting‐point glass phases (B 2 O 3 and SiO 2 ) enabled liquid‐phase self‐healing of the porous char layer. At temperatures above 1400°C, carbon thermal reduction triggered the in situ formation of ultra‐high‐temperature multiphase ceramics. These ceramics reinforced the graphitized carbon matrix, while the linear ablation rate was reduced by 35.2% relative to the EPDM/SiO 2 baseline. Overall, this study provides insights into the gas–solid evolution of SiZrB precursor‐modified EPDM composites and offers an approach for developing lightweight and robust thermal protection components for the aerospace industry.