| Silica gel is a granular, vitreous, highly porous form of | | | | Silica gel is also used to dry the air in industrial |
| silica made synthetically from sodium silicate and | | | | compressed air systems. Air from the compressor |
| despite the name is actually solid. | | | | discharge flows through a bed of silica gel beads. The |
| Silica gel is most commonly encountered in everyday | | | | silica gel adsorbs moisture from the air, preventing |
| life as beads packed in a paper sachet. In this form, it | | | | damage at the point of use of the compressed air due |
| is used as a desiccant to control local humidity in order | | | | to condensation or moisture. The same system is |
| to avoid spoilage or degradation of some goods. | | | | used to dry the compressed air on railway |
| Because of poisonous dopants and their very high | | | | locomotives, where condensation and ice in the brake |
| adsorption of moisture, silica gel packets usually bear | | | | air pipes can lead to brake failure. Silica gel is |
| warnings for the user not to eat the contents. If | | | | sometimes used as a preservation tool to control |
| consumed, the pure silica gel is unlikely to cause acute | | | | relative humidity in museum and library exhibitions and |
| or chronic illness, but would be problematic nonetheless. | | | | storage. |
| However, some packaged desiccants may include | | | | In chemistry, silica gel is used in chromatography as a |
| fungicide and pesticide poisons. Food-grade desiccant | | | | stationary phase. In column chromatography the |
| should not include any poisons which would cause | | | | stationary phase is most often composed of silica gel |
| long-term harm to humans if consumed in the | | | | particles of 40-63 ?m. Different particle sizes are used |
| quantities normally included with the items of food. | | | | for achieving a desired separation of certain molecular |
| In many items from leather to pepperoni, moisture | | | | sizes. In this application, due to silica gel's polarity, |
| encourages the growth of mold and so silica gel | | | | non-polar components tend to elute before more polar |
| sachets are used. Condensation may also damage | | | | ones, hence the name normal phase chromatography. |
| other items like electronics and may speed up the | | | | However, when hydrophobic groups are attached to |
| decomposition of chemicals, such as those in vitamin | | | | the silica gel then polar components elute first and the |
| pills. By adding packets of silica gel, these items can be | | | | method is referred to as reverse phase |
| preserved longer. Silica gel may also be used to keep | | | | chromatography. Silica gel is also applied to aluminum, |
| the relative humidity inside a high frequency radio or | | | | glass, or plastic sheets for thin layer chromatography. |
| satellite transmission system waveguide as low as | | | | Chelating groups have also been covalently bound to |
| possible. Excessive moisture buildup within a | | | | silica gel. These materials have the ability to remove |
| waveguide can cause arcing inside the waveguide | | | | metal ions selectively from aqueous media. Chelating |
| itself, damaging the power amplifier feeding it. Also, the | | | | groups can be covalently bound to polyamines that |
| beads of water that form and condense inside the | | | | have been grafted onto a silica gel surface producing |
| waveguide change the characteristic impedance and | | | | a material of greater mechanical integrity. Silica gel is |
| frequency, impeding the signal. It is common for a small | | | | also combined with alkali metals to form a M-SG |
| compressed air system to be employed to circulate | | | | reducing agent. |
| the air inside the waveguide over a jar of silica gel. | | | | |