Fumed silica and precipitated silica: an in-depth analysis of the difference between the two

Silica gel is a material widely used in industry, medicine, food and other fields. Its varied physical and chemical properties make it play an important role in various applications. The main types of silica gel include fumed silica gel and precipitated silica gel. This article will explore the differences between these two types of silica gel in detail, including their preparation methods, physical properties, chemical properties and application areas.

1. Preparation method

Fumed silica gel

Fumed silica gel is prepared by the gas phase method (also known as pyrolysis or chemical vapor deposition). The specific steps are as follows:

Raw materials: The silicon source is usually silicon tetrachloride (SiCl4) or silane (SiH4).

Process: Under high temperature environment, the silicon source gas reacts with oxygen or ammonia to produce silica particles, which are then cooled and collected in an inert gas.

Precipitated silica gel

Precipitated silica gel is prepared by the precipitation method (also known as the wet method or liquid phase method). The specific steps are as follows:

Raw materials: The silicon source is usually a silicate solution.

Process: By adding an acid or alkaline solution, the silicate ions in the silicate solution undergo a precipitation reaction to produce silica gel. The precipitate is filtered, washed, dried and calcined to obtain the final product.

2. Physical properties

Fumed silica

Specific surface area: Fumed silica has an extremely high specific surface area, usually between 500-1000 m²/g, or even higher.

Pore size distribution: The pore size distribution is narrow, mainly concentrated in the micropore range.

Particle size: The particle size is small, usually nanometers.

Particle shape: Spherical or nearly spherical particles.

Precipitated silica

Specific surface area: The specific surface area of ​​precipitated silica is low, usually between 100-500 m²/g.

Pore size distribution: The pore size distribution is wide, including micropores and mesopores.

Particle size: The particle size is large, usually micrometers.

Particle shape: Irregular shape.

3. Chemical properties

Fumed silica

Purity: Due to the high temperature and inert gas environment during the preparation process, the purity of fumed silica is high and the impurity content is extremely low.

Chemical stability: It has excellent chemical stability and is not easy to react with other chemicals.

Precipitated silica gel

Purity: The purity of precipitated silica gel is relatively low and may contain impurities introduced during the preparation process.

Chemical stability: The chemical stability is good, but not as good as that of fumed silica gel.

4. Application areas

Fumed silica gel

Catalyst carrier: Due to its high specific surface area and small pore size, fumed silica gel is widely used as a catalyst carrier.

Adsorbent: As a high-performance adsorbent in gas and liquid purification.

High-end materials: Used to prepare high-end electronic materials and optical materials.

Precipitated silica gel

Desiccant: Due to its good hygroscopicity, precipitated silica gel is often used as a desiccant.

Filler: Used as a filler in rubber and plastics to improve the mechanical properties of the material.

Food additives: Used as an anti-caking agent and rheology control agent in the food industry.

Conclusion

There are significant differences between fumed silica gel and precipitated silica gel in terms of preparation methods, physical properties, chemical properties and application areas. Fumed silica gel occupies an important position in high-end applications with its high specific surface area, excellent purity and chemical stability, while precipitated silica gel plays a role in a wide range of applications with its cost-effectiveness and versatility. Understanding the differences between these two types of silicone can help you choose the most appropriate material in your application to meet specific needs.

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