Basic Properties and Chemical Structure of Phenyl Silicone

Phenyl silicone (phenyl silicone rubber) is a specialized synthetic rubber containing a phenylene structure in its backbone. Its chemical structure enables it to exhibit excellent performance in extreme environments. In its molecular structure, silicon atoms and oxygen atoms form a stable Si-O bond, which is the basis of its unique properties. Its structural formula is HOSi(CH₃)₂O[Si(CH₃)₂O]nSi(CH₃)₂OH, and its chemical name is αω-dihydroxypolydimethylsiloxane.

Phenyl silicone rubber can be divided into three categories based on its phenyl content:
Low-phenyl silicone rubber: phenyl content 5-15%, glass transition temperature -140°C, maintains elasticity within the -70-100°C range
Medium-phenyl silicone rubber: phenyl content 15-30%, self-extinguishing
High-phenyl silicone rubber: phenyl content 30% or more, gamma-ray resistance up to 1×10⁸ roentgen

The unique properties of phenyl silicone rubber stem from the phenyl substituents in its molecular structure, which impart the following characteristics:
Wide temperature resistance (-70°C to 350°C)
Excellent ozone and oxygen aging resistance
Good electrical insulation properties
Exceptional surface properties and physiological inertness

Radiation resistance:
High-phenyl silicone rubber has a gamma-ray resistance 10-15 times that of methyl vinyl silicone rubber.
Tested at 2.58×10¹²²C/kg After gamma irradiation, the tensile strength remains at 3.6 MPa. It can withstand 1×10⁸ roentgen gamma ray irradiation without losing elasticity.

Mechanism of Radiation Stability:
The introduction of phenyl groups disrupts the regularity of the siloxane backbone, lowering the crystallization temperature.
The phenyl structure effectively absorbs gamma ray energy, reducing backbone breakage.
Materials with a high phenyl content (over 30%) perform better in radiation environments.

Comparison with Other Materials:
Ordinary silicone rubber will crack and lose strength under the same radiation dose.
High-phenyl silicone rubber has 5-10 times the radiation resistance of high-phenyl silicone rubber.

Application Examples of Phenyl Silicone in Nuclear Power Plants:
Phenyl silicone has been successfully used in key areas of several nuclear power plants:
Primary-circuit pump mechanical seals and gaskets. ‌:
As a mechanical seal material for primary circuit pumps in nuclear power plants.
Can withstand high temperatures, high pressures, and strong radiation environments.
Maintains sealing performance during long-term operation.

‌Motor Insulation Layer:
Used for insulation protection of motor equipment in nuclear power plants.
Maintains electrical insulation performance in radiation environments.
The temperature range meets nuclear power plant operating requirements.

‌Containment Penetration Seal:
As a sealing material for containment penetrations.
Can withstand LOCA (Loss of Coolant Accident) environments.
Maintains sealing integrity in high-temperature, high-pressure steam.

‌Cable Jacket:
Used as a jacket for high-temperature cables in nuclear power plants.
Provides radiation resistance, high-temperature resistance, and mechanical protection.
Oxygen index ≥28, meeting flame retardant requirements.

Comparison of Phenyl Silicone with Other Gamma-Ray-Resistant Sealing Materials
Performance Phenyl silicone rubber, ordinary silicone rubber, lead-based material, tungsten-based composite material
Gamma-ray resistance 1×10⁸ roentgen 1×10⁷ roentgen Excellent Excellent
Operating temperature range -70°C to 350°C, -60°C to 200°C, room temperature, room temperature
Density (g/cm³) 1.1-1.3 0.95-1.2 11.3 19.3
Mechanical strength (MPa) 3.6 (after irradiation) 2.0 (after irradiation) High High
Compression set Small Medium Large Large
Ease of application Excellent Excellent Poor Poor
Environmental performance Excellent Excellent Poor (lead toxicity) Excellent
Cost Medium-high Medium Low High
As can be seen from the comparison, phenyl silicone rubber has significant advantages in gamma-ray resistance, operating temperature range, and environmental performance, making it particularly suitable for dynamic sealing areas in nuclear power plants.

High-Temperature Resistance:
Long-term operating temperature up to 350°C
Short-term temperature resistance up to 400°C
Remains elastic after thousands of hours of hot air aging at 250°C

High-Pressure Stability:
Withstands the high-pressure environments encountered in nuclear power plant operations
Excellent compression-rebound properties
Good creep resistance

Radiation Aging Performance:
Remains elastic after irradiation with 1×10¹⁸ neutrons/cm²
No significant degradation in performance after long-term gamma-ray irradiation
High molecular structure stability

Chemical Stability:
Resistant to common nuclear power plant chemicals such as boric acid and detergents
Water absorption rate is only approximately 1% after long-term immersion in water
No degradation in physical properties

Phenyl Silicone Selection Recommendations for Nuclear Power Plant Sealing Materials
Based on the above analysis, phenyl silicone offers the following advantages as a gamma-ray-resistant sealing material for nuclear power plants:

Recommended Applications:
High-Radiation Areas: For areas such as the area surrounding the reactor pressure vessel, a high phenyl content (over 30%) is recommended. Silicone Rubber
In low- to medium-radiation areas, such as auxiliary equipment rooms, medium-phenyl silicone rubber can be used.
In dynamic sealing areas, such as valves and pump shafts, flexible phenyl silicone rubber seals must be used.
Performance Advantages:
Excellent gamma-ray resistance (1×10⁸ roentgen)
Wide operating temperature range (-70°C to 350°C)
Good compression-rebound properties
Excellent chemical resistance
Precautions for Use:

Select the phenyl content based on the radiation dose.
Dynamic sealing areas must ensure that the material maintains good elasticity even in irradiated environments.
Material cost savings should not be excessive in critical areas.
Future Development Directions:

Developing specialty silicone rubbers with higher phenyl content.
Optimizing material formulations to enhance radiation resistance.
Researching self-healing phenyl silicone rubber materials.
In summary, phenyl silicone, with its excellent gamma-ray resistance, wide operating temperature range, and good mechanical properties, is an ideal sealing material for nuclear power plants, particularly suitable for dynamic sealing applications in high-radiation areas.