Silica Gel, made synthetically from sodium silicate, is granular, vitreous, highly porous form of silica. Silica is a naturally occurring mineral that is purified and processed into either granular or beaded form. It has a strong affinity for water molecules.
Silica gel is commonly used as a desiccant where it is packed in vapor-permeable plastic in order to control local humidity in order to avoid spoilage or degradation of some goods. Due to their high absorption of moisture and poisonous impurities they often bear warning for the user not to eat the contents although food-grade desiccant usually does not contain any poison which would cause long term harm to humans.
Walter A. Patrick created the synthetic route for producing silica gel in 1919. It was used in gas mask canisters in World War I although it was in existence in the 1640s as a scientific curiosity. It was used in World War II to keep penicillin dry, to protect military equipment from moisture, and as a fluid cracking catalyst for the production of high octane gasoline.
The gel’s high surface area allows it to absorb water readily making it useful for saturating water although some gels will pop when exposed to enough water. The gel is blue until it is hydrated at which point it turns pink.
Many items are prone to encourage the growth of mold and condensation thus the silica gel packets preserve these items longer. The gel is often used inside high frequency radio or satellite transmission system in order to keep humidity as low as possible. If humidity builds up it can cause damage to the power amplifier feeding it. Any water can also cause degradation of the signal.
The gel is also sometimes used to control humidity in museum and library exhibitions and storage, in inhalation devices, syringes, drug test kits, and hospital sanitation kits.
Silica gel is not expected to biodegrade in either water or soil. It is also non-toxic, non-flammable, non-reactive, and stable with ordinary usage. Although non-toxic it can be irritating to the respiratory tract which may cause irritation of the digestive tract and to the skin and eyes.