Ceramization of coordinated Zr4+ and Hf4+ in polysiloxane conferring silicone/phenolic hybrid resin with excellent thermal protection

Silicon/phenolic hybrid resins are one of the most commonly used materials for thermal protection. However, the weak ability of SiO2 generated by silicone during ablation to resist the impact of high-speed hot gas flow hinders further improvement of the performance. Therefore, in this work, the ultrahigh-temperature ceramic elements Zr4+ and Hf4+ were integrated into hyperbranched polysiloxanes in the form of coordination bond and then introduced into phenolic resin (PR), obtaining hybrid resin with excellent ablative resistance. During ablation, Zr4+ and Hf4+ will first undergo ceramization, producing ZrO2 and HfO2. Subsequently, they will undergo a solid solution sintering reaction to produce complex-phase ceramic particles (ZrxHf1-x)O2, which are embedded in the SiO2 liquid film and provide excellent pinning effect. This gives the hybrid resin excellent ablation resistance, whose linear ablation rate can be as low as 0.038 mm/s, a 58 % decrease compared to pure PR. This work not only provides a new pathway for ceramization through metal ion coordination bonding, but also provides a new way to prepare high-performance TPS materials. [Display omitted] •Zr4+ and Hf4+ were successfully introduced into hyperbranched organosilica through the lone electron pair provided by C=O.•Silicon/phenolic hybrid resin with a unique nano-bicontinuous phase structure was produced.•The coordinated Zr4+ and Hf4+ can undergo in-situ ceramization and solid solution sintering reaction to produce (ZrxHf1-x)O2.•(ZrxHf1-x)O2 can perform an excellent pinning effect and confer excellent ablation resistance to the hybrid resin.