The reinforcing filler used in silicone rubber mainly refers to synthetic silica, also known as silica. Silica is divided into fumed silica and precipitated silica.

The size, specific surface area, surface properties, and structure of fumed silica particles are related to factors such as the ratio of raw gas, combustion speed, and residence time of SiO2 cores in the combustion chamber.

The finer the fumed silica particles, the larger its specific surface area, and the better the reinforcement effect, but the worse the operating performance. On the contrary, its particles are thicker and its specific surface area is smaller, so the reinforcement effect is poor, but its operability is better.

Fumed silica is one of the most commonly used reinforcing agents for silicone rubber. The rubber compound reinforced by it has high mechanical strength and good electrical properties after vulcanization. Fumed silica can be used in combination with other reinforcing agents or weak reinforcing agents to prepare rubber compounds with different application requirements.

Compared with the silicone rubber compound reinforced with fumed silica, the compound reinforced with precipitated silica has slightly lower mechanical strength and poorer dielectric properties, especially after being exposed to moisture, but is resistant to aging. The performance is better and the cost of the compound is much lower.

When the mechanical strength of the product is not high, precipitated silica can be used or it can be used in combination with fumed silica. The properties of precipitated silica are affected by precipitation conditions such as acidity, temperature, etc.

Silica can be treated with suitable compounds to make it a surface hydrophobic substance. There are two main treatment methods: liquid phase method and gas phase method. The conditions of the liquid phase method are easy to control, the product quality is stable, and the treatment effect is good, but the process is complicated and the solvent needs to be recovered; the gas phase method has a simple treatment process, but the quality of the product is not stable enough and the treatment effect is poor.