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.
