Silica gel

Silica gel is a desiccant, a substance that absorbs moisture. Despite its name, silica gel is solid. It is a naturally occurring mineral that is purified and processed into either granular or beaded form. As a desiccant, it has an average pore size of 2.4 nanometers and has a strong affinity for water molecules.

Composition

Silica gel is nearly harmless, which is why you find it in food products. Silica, or silicon dioxide (SiO2), is the same material found in quartz. The gel form contains millions of tiny pores that can adsorb and hold moisture. Silica gel is essentially porous sand.

Uses

Silica gel is most commonly encountered in everyday life as beads in a small paper packet. It is used as a desiccant to control local humidity to avoid spoilage or degradation of some goods. Because silica gel can have added chemical indicators (see below) and absorbs moisture very well, silica gel packets usually bear warnings for the user not to eat the contents.

Indicating Silica Gel

Indicating silica gel gives a visual indication of its moisture absorption by changing colors as it becomes increasingly saturated with moisture.

Regeneration

If silica gel's capacity for moisture absorption is exhausted, it can be reactivated by heating it to 120 °C (250 °F) for 1–2 hours. However, this regeneration method is long and can be basically uneconomical.

Safety

Silica gel is non-toxic, non-flammable, and non-reactive and stable with ordinary usage. It is considered to be a safe substance and is not harmful if swallowed accidentally. However, some of the beads may be doped with a moisture indicator, such as cobalt (II) chloride, which is carcinogenic.

See Also

• Desiccant
• Silicon Dioxide
• Humidity
• Cobalt(II) Chloride

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  Opalescent colloidal silica

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  Silica gel bag open with beads

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  Silica gel

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  Indicating silica gel