Silica Gel Uses
Silica Gel is a porous and amorphous form of silica or silicon dioxide. It consists of irregular and tri-dimensional oxygen and silicon atoms alternating with nanometer-scale pores and voids. The voids might contain some form of liquid or water or come filled with a vacuum or gas. In the last scenario, the material is formally called silica xerogel. The average pore size of a silica xerogel is 2.4 nanometers. It is famous for its utilisation as a desiccant and holds a strong affinity for molecules of water. It is translucent and hard but comparatively softer than massive quartz or silica glass. Plus, it retains its hard form when saturated or submerged in water.
Commercial Production
Silica xerogel is commercially available as coarse beads and granules with a diameter of a few millimetres. Some grains of Silica Gel may contain a minute amount of indicating substance. This substance indicator changes colour when it has absorbed some amount of water. You may find silica xerogel pellets in various products in a small paper envelope, usually stating a warning “do not eat.” They are an effective way to prevent dry food packages from humidity that may damage or spoil the enclosed food item. Silica Gel also comes as “wet” Silica Gel, prepared using alkali silicate solutions. Its consistency might vary from other soft transparent gels such as agar or gelatin. It can also be found in a hard solid form known as water-logged silica xerogel. Silica Gel comes in handy for specific laboratory processes such as suppression convection in liquids or preventing the settling of any suspended particles.
Types of Silica Gel
There are three basic types of Silica Gel (type 1, 2 & 3).
Type 1 desiccant is a clear pellet form with a diameter of 2.5 nanometers approximately. It has moisture-proof and drying properties and is mainly used as an absorbent, catalyst carrier, separator, etc.
Type 2 are white translucent pellets with a pore diameter ranging from 4.5 to 7.0 nanometers. Type 2 silica gel is commonly used as a dryer, liquid absorbents, and perfume carrier. Some of the other uses may include cat litter and catalyst carriers.
Type 3 is the micro-pored crystalline structure. It is a raw material to prepare Silica Gel-based cat litter. It becomes a macro-pored form of silica gel if additionally screened and dried, useful as an absorbent, drier, and catalyst carrier.
Uses of Silica Gel
Silica Gel is a beneficial substance for both consumer and commercial purposes. Below is a list of uses.
Desiccant
The most common use of Silica Gel is its use as a desiccant that comes as beads packaged in a paper or permeable bag in various products. In many products, moisture works as a catalyst to the growth of spoilage and mould. Whereas, in some, condensation may damage the items such as electronics. Similarly, condensation may also speed up the process of chemical decomposition, such as in vitamin pills. Therefore, the inclusion of Silica Gel packs in these products can help resolve these issues and preserve these products for a longer duration.
Another industrial use of Silica Gel is to keep the air dry in industrial-level compressed air systems. The air from the industrial compressor flows through a bedded layer of Silica Gel beads. These beads absorb moisture present in the air and prevent any damage the compressed air might have caused due to moisture or condensation. A similar system applies to dry the compressed air in railway locomotives, where ice and condensation in the brake’s air pipes may lead to brake failure. Silica gel is also a preservation tool to control humidity levels in library exhibitions, museums, and storage.
Other silica applications include inhalation devices, diagnostic test strips, drug test kits, syringes, and sanitation kits at the hospitals. To monitor the performance of these Silica Gels, users can choose to use a Humidity Indicator Card to keep track of the level of moisture to which the goods have been exposed.
Cat Litter
The lesser-known use of Silica Gel is its use in cat litters. Silica Gel can be used on its own or combined with other traditional materials, including clays, and it is virtually odourless.
Food Additives
Silica Gel is also known as hydrated silica or silica aerogel. The Food and Drug Authority of the United States declared it as “Generally Recognised as Safe” or “GRAS.” It means you can add it to any of the food products with any approval required by the authorities. In the US, the quantity of silica allowed in any food product is up to 2%. The permission falls under 21 CFR 172.480. Whereas, in the European Union, the maximum quantity of silica allowed in food products is 5% concentration. Some of the listed uses of silica in food products are anti-caking agent, stabiliser, defoaming agent, carrier, absorbent, conditioning agent, filter aid, viscosity control agent, emulsifying chill-proofing agent, and anti-settling agent.
Water Filtration
Due to the water adsorption capabilities of Silica Gel, it’s used with domestic water filters. Silica Gel’s surface structure makes it ideal for the adsorption of certain minerals dissolved in water, hence, commonly coined as ion exchange for marketing the product due to this characteristic.
Humidity Indicator
Silica Gel is also widely used as a moisture indicator that gradually changes its colour during its transition from a dry (anhydrous) state to a wet (hydrated) state. The most common types include methyl violet and cobalt (II) chloride. Cobalt (II) chloride is deep blue in its dry form and changes to pink when wet. However, it is carcinogenic and toxic, and the EU reclassified it as toxic material in July 2000. Methyl violet has the tendency to change its colour from orange to green and orange to colourless, depending on the conditions. Although toxic and carcinogenic, it is still comparatively safe enough for medicinal use in certain products.
Hazards of Silica Gel
Silica Gel is stable, non-reactive, non-flammable, and non-toxic with everyday use. However, it will react with strong acids, bases, and oxidisers. Silica Gel is irritating for the respiratory tract and digestive tract. The dust from Silica Gel beads may also irritate eyes and skin, therefore, the user must take precautions.