What is Silica Gel?
Silica gel is silicon dioxide (SiO2). 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 24 angstroms and has a strong affinity for moisture molecules. The silica gel will pull in moisture at temperatures up to 220°F (105°C). As temperature goes above 100°F, the rate of moisture pick-up will slow down but the silica gel will still work. Silica gel performs best at room temperatures (70° to 90°F) and high humidity (60 to 90% Rh) and will drop the relative humidity in a container down to around 40% Rh. In the United States, silica gel is commonly used in food and pharmaceutical applications as only silica gel has been approved by the FDA for direct contact with th ese items.
What is Indicating Silica Gel?
Indicating silica gel is a silica gel bead or granule that has been washed with a concentration of cobalt chloride ( a heavy metal salt). The cobalt chloride is a deep blue colour when it is dry and turns from blue to purple to pink as it becomes saturated with moisture. Typically, the colour changes as the desiccant goes past 8% moisture levels (by weight) and indicates it is time to replace the desiccant. The most typical use for an indicating silica gel is for a moisture sensitive product that will be inspected regularly as it gives a quick visual indication of how well it is doing. Because of the addition of cobalt chloride, indicating silica gel should not be used in contact with products for consumption such as food or pharmaceuticals.