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Silica gel

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	Silica gel
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	Topics Silica gel Topic Home Silica gel is a granular, porousPorosity Used in geology, hydrogeology, soil science, and building science, the porosity of a porous medium describes how densely the... form of silica made synthetically from sodium silicateSodium silicate Sodium silicate, also known as water glass or liquid glass, available in liquid and solid form, is a compound used in cement... . Despite the name, silica gel is a solid. Silica gel is most commonly encountered in everyday life as beads packed in a semi-permeableSemipermeable membrane A semipermeable membrane, also termed a selectively permeable membrane, a partially permeable membrane or a d... plastic. In this form, it is used as a desiccantDesiccant A desiccant is a hygroscopic substance that induces or sustains a state of dryness in its local vicinity in a moderately-well sea... to control local humidity in order to avoid spoilage of some goods. Because of poisonous dopantDopant A dopant, also called doping agent and dope, is an impurity element added to a semiconductor lattice in low con... s (see below) and their very high adsorptionAdsorption Adsorption is a process that occurs when a gas or liquid or solute accumulates on the surface of a solid or more rarely a l... of moisture, silica gel packets usually bear warnings for the user not to eat the contents. If consumed, the pure silica gel is unlikely to cause acute or chronic illness, but would be problematic nonetheless. However, some packaged desiccants may include fungicideFungicide A Fungicide is one of three main methods of pest control- chemical control of fungi in this case.... and/or pesticidePesticide The U.S Environmental Protection Agency defines a pesticide as "any substance or mixture of substances intended for prevent... poisons. Food-grade desiccant should not include any poisons which would cause long-term harm to humans if consumed in the quantities normally included with the items of food. A chemically similar substance with far greater porosity is aerogelAerogel Aerogel is a low-density solid-state material derived from gel in which the liquid component of the gel has been replaced wi... . History The synthetic route for silica gel was patented by chemistry professor Walter A. Patrick at Johns Hopkins UniversityJohns Hopkins University The Johns Hopkins University, founded in 1876, is a private institution of higher learning located in Baltimore, Maryland, Un... , Baltimore, MarylandBaltimore, Maryland Baltimore is an independent city located in the U.S.... in 1919. It was used in World War IWorld War I World War I, also known as the First World War, the Great War and "The War to End All Wars" was a global m... for the absorptionAbsorption Absorption may refer to:Absorption , absorption of particles of gas or liquid in liquid or solid material... of vapors and gases in gas maskGas mask Summary A gas mask* is a mask worn on the face to protect the body from airborne pollutants and toxic materials.... canisters, as part of his patent. The substance was in existence as early as the 1640s as a scientific curiosity. In World War IIWorld War II Overview World War II, or the Second World War, was a worldwide conflict fought between the Allied Powers and the Axis Powers ,... , silica gel was indispensable in the war effort for keeping penicillinPenicillin Penicillin refers to a group of -lactam antibiotics used in the treatment of bacterial infections caused by susceptible, u... dry, protecting military equipment from moisture damage, as a fluid crackingCracking (chemistry) In petroleum geology and chemistry, cracking is the process whereby complex organic molecules are converted to simpler molec... catalystCatalyst In chemistry, a catalyst is a substance that decreases the activation energy of a chemical reaction without itself being c... for the production of high octaneFacts About Octane rating The octane rating is a measure of the autoignition resistance of gasoline and other fuels used in spark-ignition internal co... gasolineGasoline Gasoline, also called petrol, is a petroleum-derived liquid mixture consisting primarily of hydrocarbons and enhanced ... , and as a catalyst support for the manufacture of butadiene from ethanolEthanol This article is about the chemical compound.... , feedstock for the synthetic rubberPolybutadiene Polybutadiene is a synthetic rubber that has a high resistance to wear and is used especially in the manufacture of tires.... program. Properties Silica gel's high surface areaSurface area Surface area is the measure of how much exposed area an object has.... (around 800 m²/g) allows it to absorb water readily, making it useful as a desiccant (drying agent). Once saturated with water, the gel can be regenerated by heating to 120 °C (250 °F) for two hours. Some types of silica gel will "pop" when exposed to enough water. Preparation A solution of sodium silicate Sodium silicate Sodium silicate, also known as water glass or liquid glass, available in liquid and solid form, is a compound used in cement... is acidified to produce a gelatinous precipitate that is washed then dehydrated to produce colorless silica gel. When a visible indication of the effectiveness of the silica gel as a desiccant is required ammonium tetracobaltate(II) or cobalt chloride, (NH₄)₂CoCl₄ is added. This is blue when anhydrous, turning pink when hydrated and this process is reversible. Applications Desiccant In many items from leather to pepperoni, 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. By adding packets of silica gel, 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 waveguideWaveguide (electromagnetism) Overview In electromagnetics and communications engineering, the term waveguide may refer to any linear structure that guides electro... as low as possible. 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, impeding 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 to the compressed air users 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. Chemistry In chemistryChemistry Chemistry is the science of matter at the atomic to molecular scale, dealing primarily with collections of atoms .... , silica gel is used in chromatographyChromatography Chromatography is the collective term for a family of laboratory techniques for the separation of mixtures.... as a stationary phaseStationary phase The term stationary phase may refer to... . In column chromatographyColumn chromatography Column chromatography in chemistry is the preparative application of chromatography.... the stationary phase is most often composed of silica gel particles of 40-63 µm. 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 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 aluminum, glass, or plastic sheets for thin layer chromatographyThin layer chromatography Thin layer chromatography is a widely-used chromatography technique used to separate chemical compounds.... . 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 alkali metalAlkali metal The alkali metals are the series of elements in Group 1 of the periodic table : lithium , sodium , potassium , rubidium , c... s to form a M-SG reducing agentM-SG reducing agent In M-SG an alkali metal is absorbed into Silica gel at elevated temperatures.... . Cat litter Silica gel is also used as cat litterCat litter Overview Cat litter is one of any of a number of materials used in litter boxes to absorb moisture from cat feces and urine, which re... , by itself or in combination with more traditional materials, such as clays including bentoniteBentonite Bentonite is an absorbent aluminium phyllosilicate generally impure clay consisting mostly of montmorillonite,0.332Si4O102&m... . It is trackless and virtually odorless, albeit expensive. Hazards Alone, silica gel is non-toxic, non-flammable and chemically unreactive. However, some of the beads may be doped with a moisture indicator, such as cobalt(II) chlorideCobalt(II) chloride Cobalt chloride is the chemical compound with the formula CoCl2, although the term is used also to refer to the hydrate, wh... , which is toxic and may be carcinogenic. Cobalt (II) chloride is deep blue when dry and pink when moist. Crystalline silica dust can cause silicosisSilicosis Silicosis is a form of pneumoconiosis caused by inhalation of crystalline silica dust, and is marked by inflammation and sca... but synthetic amorphous silica gel is non-friable, and so does not cause silicosis. External links Uses in toothpaste and other ingested consumable products Chemical properties Detailed use and re-drying info Helpful Information on Rechargeable Silica Packs for Home Usage