The study on the compatibility of phenyl silicone oil and alumina filler in high-temperature thermal grease needs to be carried out from the dimensions of chemical stability, physical compatibility, synergistic thermal conductivity, high-temperature stability and process adaptability. The following is a specific analysis:

1. Chemical stability
Characteristics of phenyl silicone oil
Phenyl silicone oil replaces part of the methyl group in methyl silicone oil with phenyl, which significantly improves its high temperature resistance, radiation resistance and oxidation stability. The introduction of phenyl in its molecular chain enhances the intermolecular force, making silicone oil difficult to decompose at high temperature, and has no chemical reaction activity with alumina filler, avoiding material degradation caused by chemical reaction.
Characteristics of alumina filler
As an inorganic non-metallic filler, alumina has high thermal conductivity (about 30 W/m·K at room temperature), chemical inertness and insulation. Its surface is usually a hydroxylated structure, which can be modified by a silane coupling agent to enhance the bonding with silicone oil, but it has no chemical interaction with phenyl silicone oil in its natural state, ensuring the chemical stability of the compatibility.

2. Physical compatibility
Surface wetting and dispersion
The high viscosity-temperature coefficient and low surface tension (about 2.1×10⁻⁴～2.85×10⁻⁴ N/cm) of phenyl silicone oil enable it to effectively wet the surface of alumina particles and reduce agglomeration. By adding silane coupling agents (such as KH-550), the interfacial tension can be further reduced, promoting the uniform dispersion of alumina in silicone oil to form a stable suspension system.
Viscosity matching
The viscosity of phenyl silicone oil can be adjusted by molecular weight (such as 50 cSt or 1000 cSt) to match the particle size distribution of alumina filler (micrometer or nanometer). High viscosity silicone oil is suitable for large particle size fillers, while low viscosity silicone oil is more conducive to the dispersion of nanometer-level fillers, thereby optimizing the construction of thermal conductive networks.

3. Synergy of thermal conductivity
Construction of thermal conductive network
Alumina fillers achieve heat conduction through phonon vibration, while phenyl silicone oil, as a matrix, assists heat transfer at the microscopic level through its thermal convection. By optimizing the filling amount of alumina (usually 55% to 70%) and the particle size distribution (such as compounding micron-grade Al₂O₃ with nano-grade BN), a dense heat conduction path can be formed, significantly improving the thermal conductivity of silicone grease (up to 3.5 to 6.5 W/m·K).
Interface thermal resistance control
The low surface tension of phenyl silicone oil reduces the gap between alumina particles and the matrix, reducing the interfacial thermal resistance. At the same time, the modification of silane coupling agent enhances the bonding force between the filler and the matrix, further optimizing the thermal conduction efficiency.

4. High temperature stability
Thermal aging performance
The gelation time of phenyl silicone oil in 250℃ hot air is as long as 1750 hours, indicating that it has excellent high temperature stability. Alumina filler does not undergo phase change or decomposition at high temperature. After the two are compounded, the silicone grease can maintain stable performance in a wide temperature range of -60℃ to 300℃, meeting the needs of high temperature applications.
Volatilization and migration control
High viscosity phenyl silicone oil or phenyl modified silicone oil can effectively reduce the volatilization rate of silicone oil and reduce the migration loss of silicone oil at high temperature, thereby maintaining the long-term stability of the thermal network.

5. Process adaptability
Processing performance
The mixing process of phenyl silicone oil and alumina requires strict control of temperature (<50℃) and shear time (2-4 hours) to prevent silicone oil oxidation and filler agglomeration. Three-roll grinding or planetary mixing process can ensure that the filler is evenly dispersed to form a stable paste.
Application performance
The compounded silicone grease needs to have low viscosity, high spreadability and shear thinning properties to facilitate construction at the interface of precision electronic components. By adjusting the addition amount of fumed silica (0.5%-5%), the rheological properties of silicone grease can be optimized to prevent sag after application.

6. Conclusion
Phenyl silicone oil and alumina filler have good compatibility in high-temperature thermal conductive silicone grease. The high temperature resistance, chemical stability and physical compatibility of phenyl silicone oil provide an excellent dispersion matrix for alumina fillers, while the high thermal conductivity of alumina significantly improves the thermal conductivity efficiency of silicone grease. By optimizing filler grading, surface modification and processing technology, high-temperature thermal conductive silicone grease with excellent thermal conductivity, strong high-temperature stability and good construction adaptability can be prepared. It is widely used in high-temperature heat dissipation scenarios such as 5G base station chips, power battery modules, and high-power LED lighting.