Silica Gel Basics

What is Silica Gel?
Silica Gel’s Main Characteristics - Adsorbability
Classification and Use of Silica Gel

What is Silica Gel?

Silica gel, namely the gel of silicon dioxide, is a highly active adsorbing material with micro-pore structure that is usually formed through the reaction between sodium silicate and sulfuric acid, polymerization and gelatinized, depurated and drying. Silica gel is a non-crystalline state substance that is mainly composed of silicon dioxide and has a certain amount of constitution water. Due to its chemical and physical structural characteristics, silica gel has many superior qualities that other similar materials can never replace, such as the adsorbability, selective absorption, and thermal stability, chemical stability, abrasion proof, dynamic resistance and so on.

Silica gel was generated in 1881 and was only used as a military material till the First World War with small-scale preparation. At the beginning of 20th century, its semi-industrialized production started. After the Second World War, as the rapid development of the modernized industries, all the industrialized countries gained impressive advances in the research and development of silica gel products. As an absorbent, dispersant, reinforcing agent, catalyzer and catalyzer carrier, silica gel has been used in many fields like the chemistry, rubber, plastic, petrol-chemistry, heavy industry, medicine and foodstuffs.

The production of silica gel started in China since 1955, after half century, from the single lump silica gel product into dozens kinds of products for various uses, such as spherical-shaped silica gel, micro-spherical shaped silica gel, activated silica gel, color-changing silica gel, big-pore silica gel, high-efficiency desiccant and so on. At present, the total domestic silica gel production capacity has reached about 100,000 tons annually, 70% of which are sold to the overseas market.

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Silica Gel’s Main Characteristics - Adsorbability

Silica gel’s absorptive action includes two processes: the absorption and the coacervation. The absorption is connected with the surface and the coacervation with the diameter of the pore. They both depend on the relative pressure of the adsorbate. Take the water vapor as an example.

Silica gel’s adsorptive capacity for the water vapor will reinforce along with the air relative humidity enhances, but the adsorptive capacity of different pore-sized silica gels have different changing rules. Under the same relative humidity, their absorptive capacity performances are variable. This kind of regular changes are usually described with the curve of adsorption isotherm, as shown below:

We can see that fine-pore silica gel has a higher adsorptive capacity under the low relative humidity; whereas the wide-pore silica gel has a relatively high adsorptive capacity under the high relative humidity. So we may choose the appropriate silica gel products according to different environments and conditions to gain the best effect.

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Classification and Use of Silica Gel

Silica gel can be classified in different ways of preparation, uses and its characteristics. By the ways of preparation, silica gels can be categorized into the silicone gel, silica sol, aerogel and the fine silica products through a deep process. By the ways of existence forms, silica gels can be categorized into liquid, powder, lump, spherical and other relative specifications. By the uses. Silica gels can be categorized into the industrial use, civil use, preparation and abruption use, chromatogram analysis use, packing use.

Silica gel’s classification by the characteristics may be done by its chemical composition, purification and pore’s physical structure. Silica gel’s characteristics and the inter-differences may greatly depend on the structural characteristics of the pores. Silica gels can be classified by the pore structure and the uses as follows: