Enhanced Ablation Resistance of Phenolic Resin at 1400–2300 °C through Zirconium-Doping-Induced Heterogeneous Melt Strengthening and Graphitization Transition

Abstract Boron oxide derived from boron-phenolic resin suffers severe viscosity reduction and volatilization at high temperatures, failing to form a robust ceramic melt layer and severely limiting its application in hypersonic vehicles. We designed a zirconium-doped polyborosilane hybrid phenolic resin (SiCBPR-Zr) featuring heterogeneous melt strengthening and catalytic graphitization. Under oxyacetylene heat flux, the inorganic segments in the cross-linked network form a viscous Zr–O–Si glass phase, followed by bond breakage to generate ZrO2 particles. These particles function as anchors within the ceramic melt, transforming it into an ultrastable, highly viscous, and interconnected multielement ceramic shield that heals cracks and promotes transition-metal-mediated graphitization. The optimized SiCBPR-Zr1‰ achieved 56.02% lower linear ablation rate (0.0263 mm/s), 25.55% lower mass ablation rate (0.0577 g/s), and 38.1 °C back-temperature reduction. Burn-through tests (4 MW/m2) showed 10.07% greater residual weight and 5.74% longer endurance. This work provides insights for high-performance thermal protection materials.