The application of phenyl silicone gum in ablative coatings is an advanced thermal protection technology based on the pyrolysis and ceramization transformation of organosilicon polymers. It is widely used in critical thermal management components of aerospace vehicles, missiles, and hypersonic aircraft.

Mechanism of Action
Phenyl silicone gum, as a phenyl-containing silicone rubber precursor, significantly enhances the thermal stability and char-forming ability of the polymer chain due to the introduction of phenyl groups (C₆H₅). Under high-temperature ablation conditions (>1500℃), its mechanism involves the following synergistic processes:

Pyrolysis and Char Formation: The phenyl structure promotes the cross-linking and graphitization of the carbon skeleton, forming a dense, continuous char layer that effectively blocks heat transfer to the substrate.
Ceramization Transformation: The siloxane main chain undergoes oxidative rearrangement at high temperatures, generating SiO₂ and silicon oxycarbide (SiOC) ceramic phases, which, in conjunction with fillers, form a high-melting-point, low-thermal-conductivity protective layer.
Heat Absorption and Gas Shielding: Polymer chain segments decompose endothermically, simultaneously releasing inert gases (such as benzene and methane), diluting oxygen concentration and forming a gaseous thermal insulation layer.
This mechanism allows the phenyl silicone gum coating to maintain structural integrity even under oxygen-rich gas erosion at 3000℃, with a significantly lower ablation rate than traditional phenolic resin systems. Typical Engineering Application Scenarios
Phenyl silicone rubber-based ablative coatings have been successfully implemented in engineering applications, primarily covering the following high-heat load scenarios:

Application Component | Functional Requirements | Typical Cases
Rocket Engine Nozzle Throat Liner | Withstands 3000°C high-temperature gas erosion, corrosion resistance | Ariane 6 engine uses 1.2 tons per unit, coating life meets multiple ignition requirements
Spacecraft Re-entry Heat Shield | Withstands atmospheric friction heat flux (>2000°C), maintains aerodynamic shape | Used in the outer thermal protection system of the re-entry capsule, achieving integrated structural-thermal protection
Satellite Optical Packaging | Withstands -120°C to 150°C thermal cycling, low thermal expansion, high light transmission stability | Phenyl silicone resin adhesive encapsulates CCD sensors, focal length shift <0.1μm
Hypersonic Vehicle Leading Edge | Resists aerodynamic shear, oxidation resistance, long-term thermal protection | Used as an inner thermal barrier material in a multi-layer composite coating system
Latest Research Progress and Composite Systems
To overcome the limitations of mechanical toughness and oxidation resistance of single phenyl silicone rubber coatings, recent research has focused on multi-component synergistic enhancement systems:

Phenyl Silicone Rubber/Phenolic Resin Composite System (PMS): A cross-linked network is constructed through hydrosilylation reaction, increasing the carbonization residue rate by more than 40%, and widening the pyrolysis temperature range to 300–800°C, forming a more stable ceramic carbon layer.
Zr-Si-O Glass Enhanced Coating: Introducing hyperbranched polysiloxane containing Zr-Si-O bonds, which generates a ZrO₂-SiO₂ composite ceramic phase at high temperatures, significantly improving laser ablation resistance and self-healing capabilities.
Borosiloxane Synergistic System: Although there is no direct literature, boron elements can promote the formation of borosilicate glass phase, enhancing the high-temperature viscosity and flow resistance of the coating, providing a key direction for future formula design. Material Performance Advantages Comparison
Material System | Maximum Temperature Resistance (°C) | Carbonization Rate (%) | Ablation Rate (mg/s) | Advantages
Phenyl Silicone Rubber-based Coating | 2800–3000 | 55–65 | 0.1–0.3 | High carbon yield, low density, good flexibility
Phenolic Resin | 2200–2500 | 40–50 | 0.5–0.8 | Low cost, but brittle
C/C Composite Material | >3000 | >70 | <0.1 | High strength, but complex preparation and high cost
Borosiloxane Modified System | 3100–3300 | 60–70 | 0.08–0.2 | Potentially optimal solution, still in the laboratory stage
Technical Challenges and Future Directions
Currently, phenyl silicone rubber-based ablative coatings still face the following key issues:

Weak interfacial bonding: Insufficient interfacial bonding strength with carbon fiber reinforcement, prone to delamination under thermal stress.
Long-term oxidative aging: In oxygen-rich, high-flow environments, the SiO₂ layer is prone to volatilization (SiO(g)), requiring the introduction of antioxidants (such as B₄C, MoSi₂).
Process complexity: High-temperature vulcanization and multi-layer coating processes require stringent equipment and environmental control.
Future research will focus on in-situ nano-ceramic reinforcement, biomimetic multi-level structural design, and intelligent self-healing coatings, promoting the evolution of phenyl silicone rubber systems towards "lightweight, high-strength, and long-life" materials.