The Classification of Silica
Silica can be divided into fumed silica and precipitated silica.
1.Fumed silica
The size, specific surface area, surface properties and structure of fumed silica particles are related to the ratio of feed gas, combustion speed and the residence time of SiO2 in combustion chamber. The finer the fumed silica particles are, the larger the specific surface area is, the better the reinforcement effect is, but the worse the operation performance is. On the contrary, its particles are thicker and its specific surface area is smaller, so its reinforcement effect is poor, but its operability is better. Fumed silica is one of the most commonly used reinforcing agents for silicone rubber. The vulcanizates reinforced by fumed silica have high mechanical strength and good electrical properties. Fumed silica can be used in combination with other reinforcing agents or weak reinforcing agents to produce different rubber materials.
The properties of precipitated silica are affected by precipitation conditions such as acidity and temperature. Compared with the silicone rubber compound reinforced by fumed silica, the mechanical strength of the compound reinforced by precipitated silica is slightly lower, the dielectric property, especially the dielectric property after being damped, is poor, but the heat-resistant aging property is better, and the cost of mixing rubber is much lower. When the mechanical strength of the product is not required to be high, it can be precipitated or mixed with fumed silica.
White carbon black can be treated by suitable compounds to make a surface hydrophobic material. There are two methods to deal with this problem: liquid phase method and gas phase method. The conditions of liquid-phase method are easy to control, the quality of products is stable and the treatment effect is good, but the process is complex and the solvent needs to be recovered; the process of gas-phase method is simple, but the quality of products is not stable enough and the treatment effect is poor.
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