Silica gel is a highly active adsorption material, usually manufactured by reacting sodium silicate with sulphuric acid, followed by ageing, acid washing and a series of post-treatment steps.
What Silica Gel Is
Silica gel is an amorphous substance with the chemical formula SiO₂·nH₂O. It is insoluble in water and in any solvent, non-toxic, odourless and chemically stable. Except for strong alkalis and hydrofluoric acid, it does not react with other substances. Its chemical composition and physical structure give it characteristics that are hard for similar materials to match: high adsorption performance, good thermal stability, chemical stability and relatively high mechanical strength.
Types by Pore Size
Silica gels are categorised according to pore diameter into large pore, coarse pore, Type B and narrow pore silica gel. Because their pore structures differ, their adsorption behaviour differs too:
| Type | Behaviour | Typical Use |
|---|
| Narrow pore silica gel | Higher adsorption at low relative humidity | General drying, gas drying |
| Coarse pore silica gel | Higher adsorption at high relative humidity | Humidity control, oil treatment |
| Type B silica gel | Between narrow and coarse pore | Catalyst carriers, fine chemicals |
| Large pore silica gel | Very large pores | Catalyst carriers, matting agents, toothpaste abrasive |
Because the pore structure of Type B silica gel sits between coarse and narrow pore, its adsorption capacity also falls between them. The right type should be selected according to your specific application.
Safety Performance
The main component of silica gel is silicon dioxide; it is chemically stable and does not burn. Silica gel is an amorphous form of silica, and workshop dust levels should be controlled below 10 mg/m³, with good ventilation and a mask worn during operation.
Silica gel has a strong adsorption capacity and can dry human skin, so suitable work clothing should be worn when handling it. If silica gel enters the eyes, rinse with plenty of water and seek medical attention promptly.
Note: Blue silica gel contains a small amount of cobalt chloride and is toxic — avoid contact with food and do not ingest. If poisoning occurs, seek medical attention immediately. Cobalt-free, colour-indicating alternatives are available and recommended for food-contact and export-to-EU applications.
