Silica gel desiccants are materials that adsorb water and are commonly used when a company wants to protect its goods from moisture damage. The main ingredient in silica gel desiccants is silicon dioxide, but some types may also contain chemicals that change color when moisture is absorbed. Typically, silica is packaged in sachets, but it is also used loosely for some applications.
Walter A. Patrick, a scientist, patented silica gel after World War I. During the war, he used it to trap dangerous gases inside gas masks. Silicon dioxide, the technical name for silica gel, had a natural proclivity to absorb moisture from the environment in addition to this application. This feature is useful for people who want to dry other objects or store goods in a dry environment.
Despite their name, silica gel desiccants are usually in the form of granules or beads, not gels. These granules can be loose or enclosed in breathable material packets. The size of the packet depends on how much air the silica is supposed to keep dry, and manufacturers frequently enclose the item in a plastic bag to keep out moisture. At about 40% of the original dry weight of the desiccant, silica can adsorb more water than another type of desiccant that uses clay.
When certain conditions are met, some silica gel desiccants include an indicator, which is a chemical that changes color when certain conditions are met. When silica gel granules are exposed to as much moisture as possible, the color of the product changes. When the silica is dry, some indicator chemicals are orange, but when it is wet, they turn green. Others change their color from orange to white. A blue silica is also available, which turns pink when fully saturated.
The granules of silica gel desiccants can be reused in their loose form, which is an advantage. The moisture in the silica can be released through drying processes such as oven heat or microwave energy. The user may be able to use the silica in the same way as before once it has dried. Desiccants that have an indicator will return to their original color.
Ingestion of most silica gels is not harmful to humans. The blue variety, on the other hand, uses a toxic chemical called cobalt chloride as an indicator. Silica gel can be found in the packaging of any product that can be damaged by moisture, from shoes to electrical goods. Silica gel desiccants may be used in drying processes such as seed preservation.