When phenyl vinyl rubber (usually referring to phenyl vinyl polysiloxane) is used as a specific substrate in hypersonic vehicle hot-end sealing materials, the core challenge lies in resolving the contradiction between "high-temperature carbonization" and "mechanical strength/erosion resistance."

Hypersonic vehicle hot ends (such as engine combustion chambers, tail nozzles, and control bays) face extreme aerodynamic heating (surface temperatures can reach 300°C~600°C or even higher) and particle erosion from high-speed airflow.

Optimization of the erosion resistance of phenyl vinyl rubber-based hot-end sealing materials typically follows a strategy of "main chain heat resistance modification + filler reinforcement + functional synergy." The specific optimization directions and technical paths are as follows:

1. Heat Resistance Upgrade of the Base Polymer (Source Modification)
The introduction of phenyl is intended to break the regularity of the polysiloxane main chain and improve heat resistance. For hot-end applications, further refinement of phenyl content is typically required:

* High phenyl content: Increasing the phenyl content (e.g., a phenyl molar fraction of 30%~50% or even higher) can significantly improve the thermal oxidative stability of raw rubber, as phenyl is a rigid group that effectively hinders the thermal degradation and rearrangement of the main chain.

* Side-chain vinyl regulation: Vinyl groups primarily provide crosslinking activity. In hot-end applications, crosslinking density needs to be balanced. Excessively high crosslinking density may cause the material to become brittle under thermal shock; therefore, moderate crosslinking is usually used to maintain a certain level of toughness to resist the pressure of airflow pulsations.

2. Reinforcing filler system (the core of erosion resistance) Erosion resistance is essentially a test of the material's surface hardness and toughness. Pure silicone rubber is easily worn by dust particles carried by high-speed airflow and must be reinforced with fillers:

* Nanoscale reinforcing fillers:
* Fumed silica (surface-treated with hexamethyldisilazane, etc.): This is the most crucial reinforcing filler, significantly improving the tear strength and abrasion resistance of the rubber compound.
* Silicon carbide whiskers/nanowires: Introducing silicon carbide fillers with high aspect ratios, utilizing their high hardness and high thermal conductivity, not only improves the material's rigidity to resist particle cutting but also rapidly dissipates heat from localized hot spots through thermal conductivity, preventing localized overheating and carbonization failure.

* Layered fillers:
* Modified boron nitride (BN) or molybdenum disulfide (MoS₂): These lamellar fillers can form a "labyrinth" structure within the material, hindering crack propagation while providing certain self-lubricating and wear-resistant properties.


3. Synergistic System of Ablation Resistance and Erosion Resistance
At the hypersonic hot end, simple "wear resistance" is insufficient; "ablation resistance" is also required. Optimization schemes often draw on the design concepts of ablative materials:

* Introducing ablative fillers:
* Phenolic resin microspheres or hollow microspheres: At high temperatures, phenolic resin carbonizes to form a carbon skeleton, which combines with the ceramicized residue of silicone rubber to form a hard ceramic carbon layer. This carbon layer acts as an "armor" against high-speed airflow erosion.

* Glass microspheres (hollow or solid): Melted at high temperatures to form a glassy glaze layer, sealing surface pores, improving surface density, and reducing mass ablation rate.

* Ceramic precursors: Introducing polycarbosilanes or modified polysilazanes, blended with phenyl vinyl raw rubber, to generate SiC or Si₃N₄ ceramic phases in situ at high temperatures, greatly improving the strength of residual carbon.

4. Structural Design and Process Optimization
* Functionally graded materials (FGM): Since hot-end seals typically connect high-temperature and room-temperature zones, a layered or gradient structure is designed. A high-filler content, high-ceramization-prone formulation is used on the high-temperature side, while a highly elastic pure rubber material is used on the low-temperature side to achieve stress buffering.

* Surface treatment: Plasma treatment or coating with a high-temperature resistant coating (such as a zirconium-containing silicone resin coating) is applied to the surface of the vulcanized seal to further improve surface hardness.