Silica gel is a naturally occurring mineral that is purified and processed into either a granular or beaded form. It is a transparent, porous form of silicon dioxide made artificially from sodium silicate. Silica gel has a very high affinity for water molecules.You will most commonly encounter silica gel in a bead form packaged in small paper packets. It is used as a desiccant to control humidity in a package to avoid goods being spoiled.
Uses of Silica Gel
Moisture encourages the growth of mold and spoilage in many items and condensation may also damage items such as electronics and may speed the decay of chemicals such as those in vitamins. The inclusion of silica gel packs allow these items to be preserved for longer periods of time, especially during shipping and/or storage.Silica gel may also be used to keep the relative humidity inside a high frequency radio or satellite transmission system waveguide as low as possible. Commonly, a waveguide is a hollow metal pipe used to carry radio waves. Excessive moisture within a waveguide can cause arcing or degrade the signal.In industrial compressed air systems, silica gel is used to control condensation and moisture in the air. The air from the compressor discharge flows through silica gel beads that adsorb moisture from the air, thus preventing damage at the point of use.Sometimes, silica gel is used as a preservation tool by museums and libraries to control humidity during exhibitions and storage.
Silica gel was used in both World Wars. In World War I, it was used in gas mask canisters to adsorb vapors and gases and in the Second World War, it was essential for keeping penicillin dry and for protecting military equipment from moisture damage.It is also used as a safe way to help preserve food.
Indicating Silica Gel – color changing gel as an effectiveness gauge
Silica gel may contain chemical additives such as cobalt (II) chloride or methyl violet that act as moisture indicators. These chemicals change color as the silica gel changes from dry to wet, allowing users to determine when it needs to be replaced. Cobalt (II) chloride is dark blue in color when dry and pink when wet. Methyl violet can be made to change from either orange to green or from orange to colorless. Both of these chemicals are toxic and carcinogenic but are safe enough to have medicinal uses.
Consequently, silica gel packets are usually printed with a warning not to eat the contents.