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Application of Silica gel
Silica gel is a commonly used desiccant as beads packed in a permeable bag
In many items, moisture encourages the growth of mold and spoilage. Condensation may also damage other items like electronics and may speed the decomposition of chemicals, such as those in vitamin pills. Through the inclusion of silica gel packets, these items can be preserved longer.
Silica gel may also be used to keep the
(RH) inside a high frequency radio or satellite transmission system
as low as possible (see also
). Excessive moisture buildup within a waveguide can cause arcing inside the waveguide itself, damaging the power amplifier feeding it. Also, the beads of water that form and condense inside the waveguide change the characteristic impedance and frequency, degrading the signal. It is common for a small compressed air system (similar to a small home aquarium pump) to be employed to circulate the air inside the waveguide over a jar of silica gel.
Silica gel is also used to dry the air in industrial compressed air systems. Air from the compressor discharge flows through a bed of silica gel beads. The silica gel adsorbs moisture from the air, preventing damage at the point of use of the compressed air due to condensation or moisture. The same system is used to dry the compressed air on railway locomotives, where condensation and ice in the brake air pipes can lead to brake failure.
Silica gel is sometimes used as a
tool to control relative humidity in museum and library exhibitions and storage.
Other applications include diagnostic test strips, inhalation devices,
drug test kits
and hospital sanitation kits.
In chemistry, silica gel is used in
, the stationary phase is most often composed of silica gel particles of 40–63 μm. Different particle sizes are used for different kinds of column chromatography as the particle size is related to surface area. The differences in particle size dictate if the silica gel should be used for flash or gravity chromatography. In this application, due to silica gel's polarity, non-polar components tend to
before more polar ones, hence the name
normal phase chromatography
. However, when
groups (such as C18 groups) are attached to the silica gel then polar components elute first and the method is referred to as
reverse phase chromatography
. Silica gel is also applied to
, or plastic sheets for
thin layer chromatography
The hydroxy (OH) groups on the surface of silica can be functionalized to afford specialty silica gels that exhibit unique stationary phase parameters. These so-called functionalized silica gels are also used in organic synthesis and purification as insoluble reagents and
Chelating groups have also been covalently bound to silica gel. These materials have the ability to remove metal ions selectively from aqueous media. Chelating groups can be covalently bound to polyamines that have been grafted onto a silica gel surface producing a material of greater mechanical integrity. Silica gel is also combined with
to form a
M-SG reducing agent
Silica gel is not expected to biodegrade in either water or soil.
Silica gel is also used as
, by itself or in combination with more traditional materials, such as clays including
. It is non-tracking and virtually odorless.
Silica gel, also referred to as silica aerogel or hydrated silica, is listed by the FDA in the United States as
generally recognized as safe
(GRAS), meaning it can be added to food products without needing approval. Silica is allowed to be added to food in the US at up to 2% as permitted under 21 CFR 172.480. In the EU it can be in up to 5% concentrations.
Listed uses include: anticaking agent, defoaming agent, stabilizer, adsorbent, carrier, conditioning agent, chillproofing agent, filter aid, emulsifying agent, viscosity control agent, and anti-settling agent.
Given the water adsorption properties of silica gel, it is used in domestic water filters. The surface structure of silica gel allows the adsorption of some minerals which are dissolved in the water, or "Ion-exchange" as it is marketed. Due to the lack of regulations for domestic water filtration products, no studies validate the manufacturer claims regarding the effectiveness of the filtration system.
Humidity indicator (blue/orange silica gel)
Indicating silica gel
Silica gel may be doped with a moisture indicator that gradually changes its color when it transitions from the
(dry) state, to the
(wet) state. Common indicators are
. Cobalt (II) chloride is deep blue when dry and pink when wet, but it is toxic and carcinogenic, and was reclassified by the
in July 2000 as a toxic material.
can be formulated to change from orange to green, or orange to colorless. It is also toxic and potentially carcinogenic, but is safe enough to have medicinal uses.
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