Due to the flexible nature of its backbone structure, high-temperature vulcanized (HTV) silicone rubber—in its pure, vulcanized form—exhibits extremely low tensile strength (typically under 0.5 MPa), rendering it of little practical value. The addition of white carbon black (precipitated or fumed silica) can boost its strength by tens of times, exceeding 10 MPa; this transformative effect is known as reinforcement.

Reinforcement Mechanism
The reinforcement provided by white carbon black stems primarily from its immense specific surface area and surface activity.

- **Physical Adsorption:** White carbon black particles are extremely small (nanoscale) with a large specific surface area and surfaces rich in silanol groups. These active sites strongly adsorb silicone rubber molecular chains, forming "bound rubber."
- **Network Structure:** White carbon black particles form a three-dimensional network structure within the rubber matrix, restricting the slippage of molecular chains. When the material is subjected to force, stress is effectively transferred to the rigid white carbon black particles, thereby significantly increasing the material's modulus and strength.

Comparison: Fumed vs. Precipitated Silica
- **Fumed Silica:** Features extremely high purity (>99.8%), smaller primary particle sizes, and a large specific surface area. It offers excellent reinforcement, imparting superior tear resistance, high transparency, and high mechanical strength to HTV silicone rubber; however, it entails higher costs and results in higher processing viscosity.
- **Precipitated Silica:** Offers lower costs. While its reinforcing effect is slightly inferior to that of fumed silica, it provides better heat-aging resistance. It is widely used in standard molded products where transparency requirements are moderate and cost-effectiveness is prioritized.

Conclusion
White carbon black is an indispensable reinforcing agent for HTV silicone rubber. By selecting the appropriate type of white carbon black and modifying it with silane coupling agents, manufacturers can significantly enhance the tensile strength, hardness, and wear resistance of the silicone rubber, enabling it to meet the rigorous demands of applications such as industrial seals, keypads, and cables.