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Encyclopedia > Silica gel
Beads of silica gel
Beads of silica gel

Silica gel is a granular, porous form of silica made synthetically from sodium silicate. Despite the name, silica gel is a solid. Image File history File linksMetadata Download high-resolution version (2256x1052, 165 KB) Beads of Silica Gel File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Silica gel User:Henningklevjer User:Dothefandango Wikipedia:Userboxes/Food User:Zowayix User:Batchelor User... Image File history File linksMetadata Download high-resolution version (2256x1052, 165 KB) Beads of Silica Gel File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Silica gel User:Henningklevjer User:Dothefandango Wikipedia:Userboxes/Food User:Zowayix User:Batchelor User... Porosity is a measure of the void spaces in a material, and is measured as a fraction, between 0–1, or as a percent between 0–100%. The term porosity is used in multiple fields including manufacturing, earth sciences and construction. ... The chemical compound silicon dioxide, also known as silica, is the oxide of silicon, chemical formula SiO2. ... Sodium silicate, also known as water glass or liquid glass, available in aqueous solution and in solid form, is a compound used in cements, passive fire protection, refractories, textile and lumber processing. ...


Silica gel is most commonly encountered in everyday life as beads packed in a semi-permeable plastic. In this form, it is used as a desiccant to control local humidity in order to avoid spoilage of some goods. Because of poisonous dopants (see below) and their very high absorbtion of moisture, silica gel packets usually bear warnings for the user not to eat the contents, but to throw them away instead. 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 fungicide and/or pesticide poisons. It is not known whether these would be labelled specifically. 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. Scheme of semipermeable membrane during hemodialysis, where red is blood, blue is the dialysing fluid, and yellow is the membrane. ... A desiccant is a substance that adsorbs moisture from the air. ... A dopant, also called doping agent and dope, is an impurity element added to a semiconductor lattice in low concentrations in order to alter the optical/electrical properties of the semiconductor. ... A Fungicide is one of three main methods of pest control- chemical control of fungi in this case. ... A cropduster spreading pesticide. ... This article is about the dangerous substance. ...

Contents

History

Silica gel was patented by chemistry professor Walter A. Patrick at Johns Hopkins University, Baltimore, Maryland in 1919. Prior to that, it was used in World War I for the adsorption of vapors and gases in gas mask canisters. The substance was in existence as early as the 1640s as a scientific curiosity.[1] The Johns Hopkins University, founded in 1876, is a private institution of higher learning located in Baltimore, Maryland, United States. ... Nickname: Monument City, Charm City, Mob Town[1][2], B-more Motto: The Greatest City in America,[3] Get in on it. ... This article is becoming very long. ... Adsorption is a process that occurs when a gas or liquid or solute (called adsorbate) accumulates on the surface of a solid or more rarely a liquid (adsorbent), forming a molecular or atomic film (adsorbate). ... Belgian 1930s era L.702 model civilian mask A gas mask is a poo worn on the face to protect the body from airborne pollutants and toxic materials. ...


In World War II, silica gel was indispensable in the war effort for keeping penicillin dry, protecting military equipment from moisture damage, 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 the synthetic rubber program. Combatants Allied powers: China France Great Britain Soviet Union United States and others Axis powers: Germany Italy Japan and others Commanders Chiang Kai-shek Charles de Gaulle Winston Churchill Joseph Stalin Franklin Roosevelt Adolf Hitler Benito Mussolini Hideki Tōjō Casualties Military dead: 17,000,000 Civilian dead: 33,000... Penicillin nucleus Penicillin (sometimes abbreviated PCN) refers to a group of β-lactam antibiotics used in the treatment of bacterial infections caused by susceptible, usually Gram-positive, organisms. ... Factory of Shukhov cracking process, Baku, USSR, 1934 In petroleum geology and chemistry, cracking is the process whereby complex organic molecules such as kerogens or heavy hydrocarbons are broken down into simpler molecules (e. ... It has been suggested that this article or section be merged into Catalysis. ... A gas station pump offering five different octane ratings. ... Gasoline or petrol is a petroleum-derived liquid mixture consisting mostly of hydrocarbons and enhanced with benzene or iso-octane to increase octane ratings, used as fuel in internal combustion engines. ... Butadiene can refer to either one of two hydrocarbon chemical compounds which are alkenes that are isomers of each other. ... Ethanol, also known as ethyl alcohol, drinking alcohol or grain alcohol, is a flammable, colorless, slightly toxic chemical compound with a distinctive perfume-like odor, and is the alcohol found in alcoholic beverages. ... Polybutadiene is a synthetic rubber that has a high resistance to wear and is used especially in the manufacture of tires. ...


Properties

Some examples of silica gel sachets

Silica gel's high surface area (around 800 m²/g) allows it to adsorb water readily, making it useful as a desiccant (drying agent). Once saturated with water, the gel can be regenerated by heating to 150 °C (300 °F) for 1.5 hours per litre of gel. Some types of silica gel will "pop" when exposed to enough water. Some samples of silica gel File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Some samples of silica gel File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Adsorption is a process that occurs when a gas or liquid or solute (called adsorbate) accumulates on the surface of a solid or more rarely a liquid (adsorbent), forming a molecular or atomic film (adsorbate). ... A desiccant is a substance that adsorbs moisture from the air. ...


Applications

Desiccant

See also: 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 sachets of silica gel, these items can be preserved longer. A desiccant is a substance that adsorbs moisture from the air. ...


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. 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. It has been suggested that this article or section be merged with Waveguide (optics). ...


Chemistry

In chemistry, silica gel is used in chromatography as a stationary phase. In column 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 or plastic sheets for thin layer chromatography. This article or section includes a list of works cited or a list of external links, but its sources remain unclear because it lacks in-text citations. ... Pictured is a sophisticated gas chromatography system. ... Chromatography is a family of analytical chemistry techniques for the separation of mixtures. ... Column chromatography in chemistry is the preparative application of chromatography. ... A HPLC. From left to right: A pumping device generating a gradient of two different solvents, a steel enforced column and an apparatus for measuring the absorbance. ... In chemistry, hydrophobic or lipophilic species, or hydrophobes, tend to be electrically neutral and nonpolar, and thus prefer other neutral and nonpolar solvents or molecular environments. ... A HPLC. From left to right: A pumping device generating a gradient of two different solvents, a steel enforced column and an apparatus for measuring the absorbance. ... Separation of black ink on a TLC plate. ...


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 metals to form a M-SG reducing agent. The alkali metals are the series of elements in Group 1 (IUPAC style) of the periodic table (excluding hydrogen in all but one rare circumstance): lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). ... In M-SG an alkali metal is absorbed into Silica gel at elevated temperatures. ...


Cat litter

Silica gel is also used as cat litter, by itself or in combination with more traditional materials, such as clays including bentonite. It is trackless and virtually odorless, albeit expensive. A packet of clumping cat litter & a litter box Cat litter is one of any of a number of materials used in litter boxes to absorb moisture from cat feces and urine, which reduces foul odors such as ammonia and renders them more tolerable within human dwellings. ... Bentonite - USGS Bentonite is an absorbent aluminium phyllosilicate generally impure clay consisting mostly of montmorillonite, (Na,Ca)0. ...


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) chloride, which is toxic and may be carcinogenic. Cobalt (II) chloride is deep blue when dry (anhydrous) and pink when moist (hydrated). This is one reason most silica gel packets are labeled as dangerous or poisonous when eaten. Cobalt(II) chloride (CoCl2) is a chemical compound composed of cobalt and chlorine. ... In pathology, a carcinogen is any substance or agent that promotes cancer. ... As a general term, a substance is said to be anhydrous if it contains no water. ... Hydrates are compounds formed by the union of water with some other substance, generally forming a neutral body, as certain crystallized salts. ...


Crystalline silica dust can cause silicosis[citation needed] but synthetic amorphous silica, which is what silica gel is, does not cause silicosis .[citation needed] A chemically similar substance with far greater porosity is aerogel. Silicosis (also known as Grinders disease) is a form of pneumoconiosis caused by inhalation of crystalline silica dust, and is marked by inflammation and scarring in forms of nodular lesions in the upper lobes of the lungs. ... A 2. ...


References

  1. ^ Maryann Feldman and Pierre Desrochers (March 2003). "Research Universities and Local Economic Development: Lessons from the History of the Johns Hopkins University". Industry and Innovation 10 (1, 5–24). 

External links

  • Links to external chemical sources

 
 

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