What is Silica Gel?
Silica gel, a highly porous, noncrystalline form of silica used to remove moisture from gases and liquids, to thicken liquids, to impart a dull surface to paints and synthetic films, and for other purposes. Silica gel was known as early as , but it remained a curiosity until its adsorbent. Mar 09, · The gel itself is basically a mix of water and silica, the main component of sand. Together, the ingredients create pellets that, when examined closely, are made of molecular nets and have almost spongelike structure. All the tiny gaps among and between these molecules are what allows the gel to hold onto water so well.
Silica what is silica gel made ofa highly porous, noncrystalline form of silica used to remove moisture from gases and liquids, to thicken liquids, to impart a dull surface to paints and synthetic films, and for other purposes. Silica gel was known as early asbut it remained a curiosity until its adsorbent properties were found useful in gas masks during What veterans day means to me War I.
It is generally prepared by acidification of a solution of a silicate, such as water glass; the resulting silicic acid forms either a rigid mass or a gelatinous precipitate from which soluble materials are removed by washing with water. The water is finally removed by heating, leaving a glassy, granular solid. For highest activity as a desiccant, the gel is not completely dehydrated but is left with a small percentage of combined water.
The true density of silica is 2. A common commercial form has a bulk density of about 0. Silica gel. Additional Info. More About Contributors Whqt History. Home Science Qhat Silica gel chemical compound. Print Cite verified Cite. While every effort has been made to follow citation style rules, there may silia some discrepancies. Please refer to the appropriate style manual or other sources if you have any questions.
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Learn More in these related Britannica articles:. Silica gel served as the granular solid, and Martin and Synge pictured the gel as composed of water tightly bonded to the crystals of silica; the mobile phase was ix.
Their work with this technique was remarkably successful. Although their method was mechanically identical with…. This solution is gently brushed between and over every petal. Since this method of drying does not preserve the stems, the flower heads must ge, wired before they are arranged. History at your fingertips. Sign up here to see what happened On This Dayevery day in your inbox!
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It is made of a long polymeric chain similar to the formula H O ? S i ? O ? (S i ? O) n ? S i ? O ? S i ? O H, with supplementary negatively charged Oxygen atoms above and under each Silicon atoms. The whole chain is negatively charged. Jan 26, · Silica gel is a substance made from silicon silicate that is known for its ability to absorb and hold in moisture. Even though the term silica gel is used to describe this particular type of silica substance, it is actually a solid rather than a gel. Silica gel: – mesh, pore size A, pore cm3 /g, active surface m 2/g. Before use, the silica gel is serially rinsed with acetone, hexane, and dichloromethane, completely dried in a fumehood, and activated for 20 h at –°C. Columns are then preconditioned using 20 mL of hexane.
Silica gel is an amorphous and porous form of silicon dioxide silica , consisting of an irregular tridimensional framework of alternating silicon and oxygen atoms with nanometer -scale voids and pores.
The voids may contain water or some other liquids, or may be filled by gas or vacuum. In the last case, the material is properly called silica xerogel. Silica xerogel with an average pore size of 2. It is hard and translucent , but considerably softer than massive silica glass or quartz ; and remains hard when saturated with water. Silica xerogel is usually commercialized as coarse granules or beads, a few millimeters in diameter.
Some grains may contain small amounts of indicator substance that changes color when they have absorbed some water. Small paper envelopes containing silica xerogel pellets, usually with a "do not eat" warning, are often included in dry food packages to absorb any humidity that might cause spoilage of the food. It is sometimes used in laboratory processes, for example to suppress convection in liquids or prevent settling of suspended particles.
Silica gel was in existence as early as the s as a scientific curiosity. Patrick at Johns Hopkins University in In World War II , silica gel was indispensable in the war effort for keeping penicillin dry, protecting military equipment from moisture damage, [ citation needed ] as a fluid cracking catalyst for the production of high octane gasoline , and as a catalyst support for the manufacture of butadiene from ethanol feedstock for synthetic rubber production. Silica alumina gel - light yellow, chemically stable, flame-resistant, insoluble except in alkali or hydrofluoric acid.
Superficial polarity, thermal stability, performance greater than fine-pored silica gel. Stabilizing silica gel - non-crystalline micro-porous solid powder, nontoxic, flame-resisting, used in brewery of grains for beer to improve taste, clearness, color and foam, removal of non-micro-organism impurities.
Silica gel is often described as "absorbing" moisture, which may be appropriate when the gel's microscopic structure is ignored, as in silica gel packs or other products. However, material silica gel removes moisture by adsorption onto the surface of its numerous pores rather than by absorption into the bulk of the gel.
This is caused by breakage of the silica spheres when contacting the water. An aqueous solution of sodium silicate is acidified to produce a gelatinous precipitate that is washed, then dehydrated to produce colorless silica gel.
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 relative humidity inside a high frequency radio or satellite transmission system waveguide as low as possible see also humidity buffering. 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 preservation tool to control relative humidity in museum and library exhibitions and storage.
Other applications include diagnostic test strips, inhalation devices, syringes , drug test kits and hospital sanitation kits. In chemistry, silica gel is used in chromatography as a stationary phase. 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 elute before more polar ones, hence the name normal phase chromatography. However, when hydrophobic groups such as C 18 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 aluminium , glass , 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 scavengers.
Chelating groups have also been covalently bound to silica gel. These materials have the ability to remove metal ions selectively from aqueous solutions. 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 alkali metals to form a M-SG reducing agent. See SiGNa chemistry. Silica gel is not expected to biodegrade in either water or soil. Silica gel is also used as cat litter ,  by itself or in combination with more traditional materials, such as clays including bentonite.
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.
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.
Due to the lack of regulations for domestic water filtration products, no studies validate the manufacturer claims regarding the effectiveness of the filtration system. Silica gel may be doped with a moisture indicator that gradually changes its color when it transitions from the anhydrous dry state, to the hydrated wet state. Common indicators are cobalt II chloride and methyl violet. Cobalt II chloride is deep blue when dry and pink when wet, but it is toxic and carcinogenic, and was reclassified by the European Union in July as a toxic material.
It is also toxic and potentially carcinogenic,  but is safe enough to have medicinal uses. Silica gel is non-toxic, non-flammable, and non-reactive and stable with ordinary usage. It will react with hydrogen fluoride , fluorine , oxygen difluoride , chlorine trifluoride , strong acids, strong bases, and oxidizers. Additional hazards may occur when doped with a humidity indicator. From Wikipedia, the free encyclopedia. Chemical formula. Chemical compound.
Type A — clear pellets, approximate pore diameter: 2. Type B — translucent white pellets, pore diameter: 4. Type C — translucent, micro-pored structure, raw material for preparation of silica gel cat litter. Additionally dried and screened, it forms macro-pored silica gel which is used as drier, adsorbent and catalyst carrier.
See also: Desiccant. Main article: Humidity indicator. Henisch : Crystals in Gels and Liesegang Rings. Cambridge University Press. Industry and Innovation. S2CID Archived from the original PDF on Chemistry of the Elements 2nd ed. ISBN Archived from the original on Retrieved USA Today. Archived from the original PDF on April 18, Archived from the original PDF on April 9, Peri , A.
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