Zinc Borate/Zirconium Carbide-Modified Liquid Silicone Rubber for Flexible Thermal Protection: Glassy Bonding and Ceramic Skeleton Effects

Char residue layers formed from silicone-rubber-based ablation protection materials are often loose and mechanically weak. Herein, addition-cured liquid silicone rubber (LSR) was synergistically modified with zinc borate (ZB) as a glass-forming bonding filler and zirconium carbide (ZrC) as a high-temperature ceramic filler. Six formulations were designed to clarify the ZB/ZrC synergistic mechanism. ZrC was uniformly dispersed without macroscopic sedimentation, and all modified samples showed elongations at break above 150%. After ZB incorporation, the IZrC/IZrO2 ratio of oxyacetylene-ablated char residues increased from 0.834–0.957 to 1.125–1.524, indicating suppressed excessive oxidation of ZrC. Under 1000 °C butane flame ablation, 15ZB/10ZrC achieved the optimal overall performance, with a peak back-face temperature of approximately 109 °C and a mass ablation rate of 0.0050 g/s. The improved ablation resistance is attributed to a glass-phase-mediated ceramic skeleton stabilization mechanism that forms a porous glassy-ceramic protective shell.