Silica gel is a granular, porous form of silica made synthetically from sodium silicate. Porosity is a measure of the void spaces in a material and is measured as a fraction between 0–1 or as a Percentage between 0–100% The Chemical compound silicon dioxide, also known as silica or silox (from the Latin " Silex " is an Oxide E550 redirects here For the Italian locomotive see FS Class E550 Sodium silicate, also known as water glass or liquid glass, available Despite the name, silica gel is a solid.
Silica gel is most commonly encountered in everyday life as beads packed in a semi-permeable plastic. A semipermeable membrane, also termed a selectively-permeable membrane, a partially-permeable membrane or a differentially-permeable membrane, is a membrane In this form, it is used as a desiccant to control local humidity in order to avoid spoilage of some goods. A Desiccant is a Hygroscopic substance that induces or sustains a state of dryness ( Desiccation) in its local vicinity in a moderately-well sealed container Because of poisonous dopants (see below) and their very high absorption of moisture, silica gel packets usually bear warnings for the user not to eat the contents. A dopant, also called doping agent and dope, is an impurity element added to a crystal or semiconductor lattice in low concentrations in order to alter the optical/electrical 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. Fungicides are Chemical compounds or biological organisms used to kill or inhibit fungi or fungal spores A pesticide is a substance or mixture of substances used to kill a pest. In the context of Biology, poisons are substances that can cause damage, Illness, or Death to Organisms usually by 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.
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History
Silica gel was patented by chemistry professor Walter A. Patrick at Johns Hopkins University, Baltimore, Maryland in 1919. It was used in World War I for the absorption of vapors and gases in gas mask canisters, as part of his patent. World War I (abbreviated WWI; also known as the First World War, the Great War, and the War to End All A gas mask is a Mask worn over the face to protect the wearer from inhaling airborne Pollutants and Toxic materials The substance was in existence as early as the 1640s as a scientific curiosity. [1]
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. World War II, or the Second World War, (often abbreviated WWII) was a global military conflict which involved a majority of the world's nations, including Penicillin (sometimes abbreviated PCN or pen) is a group of Beta-lactam antibiotics used in the treatment of Bacterial Infections In Petroleum geology and Chemistry, cracking is the process whereby complex organic Molecules such as Kerogens or heavy Hydrocarbons Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst The octane rating is a measure of the resistance of Gasoline and other Fuels to Detonation ( Engine knocking) in spark-ignition Polybutadiene is a Synthetic rubber that is a Polymer formed from the Polymerization of the Monomer 13-butadiene.
Properties
Silica gel's high surface area (around 800 m²/g) allows it to absorb water readily, making it useful as a desiccant (drying agent). Surface area is the measure of how much exposed Area an object has 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.
Applications
Desiccant
- See also: Desiccant
In many items from leather to pepperoni, moisture encourages the growth of mold and spoilage. A Desiccant is a Hygroscopic substance that induces or sustains a state of dryness ( Desiccation) in its local vicinity in a moderately-well sealed container 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.
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. In Electromagnetics and communications engineering, the term waveguide may refer to any linear structure that guides electromagnetic waves 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 preservation tool to control relative humidity in museum and library exhibitions and storage. Preservation is a branch of Library and information science concerned with maintaining or restoring access to artifacts documents and records through the study diagnosis treatment
Chemistry
In chemistry, silica gel is used in chromatography as a stationary phase. Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties Chromatography (from Greek χρώμα chroma, color and γραφειν"graphein" to write is the collective term for a family of Laboratory The term stationary phase may refer to Stationary phase (biology, a phase in bacterial growth Stationary phase (chemistry, a medium used In column chromatography the stationary phase is most often composed of silica gel particles of 40-63 μm. Column chromatography in Chemistry is a method used to purify individual Chemical compounds from mixtures of compounds 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. High-performance liquid chromatography (or High pressure liquid chromatography, HPLC) is a form of Column chromatography used frequently in Biochemistry 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. In Chemistry, hydrophobicity (from the combining form of water in Attic Greek hydro- and for fear phobos) refers to the physical property of High-performance liquid chromatography (or High pressure liquid chromatography, HPLC) is a form of Column chromatography used frequently in Biochemistry Silica gel is also applied to aluminum or plastic sheets for thin layer chromatography. Thin layer chromatography (TLC is a Chromatography technique used to separate mixtures
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. Trends The alkali metals show a number of trends when moving down the group - for instance decreasing electronegativity increasing reactivity and decreasing melting and boiling In M-SG an Alkali metal is absorbed into Silica gel at elevated temperatures
Cat litter
Silica gel is also used as cat litter[2], by itself or in combination with more traditional materials, such as clays including bentonite. Cat litter (often called kitty litter) is one of any of a number of materials used in Litter boxes to absorb moisture from Cat Feces and Bentonite is an absorbent Aluminium phyllosilicate generally impure Clay consisting mostly of Montmorillonite. 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) chloride, which is toxic and may be carcinogenic. Cobalt(II chloride is the Chemical compound with the formula Co[[chlorine Cl2]] although the term is used also to refer to the hexahydrate which The term carcinogen refers to any substance Radionuclide or radiation that is an agent directly involved in the promotion of Cancer or in the fatation of its propagation Cobalt (II) chloride is deep blue when dry (anhydrous) and pink when moist (hydrated). As a general term a substance is said to be anhydrous if it contains no Water. Hydrate is a term used in Inorganic chemistry and Organic chemistry to indicate that a substance contains Water.
Crystalline silica dust can cause silicosis but synthetic amorphous silica gel is non-friable, and so does not cause silicosis. Silicosis (also known as Grinder's disease and Potter's rot) is a form of Occupational lung disease caused by inhalation of crystalline Silica Friability means the ability to reduce a Solid substance into smaller pieces with little effort A chemically similar substance with far greater porosity is aerogel. Aerogel is a low-density solid-state material derived from Gel in which the liquid component of the gel has been replaced with gas
References
- ^ 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).
- ^ Andrew Kantor (2004-12-10). "MMIV" redirects here For the Modest Mouse album see " Baron von Bullshit Rides Again " Events 1041 - Empress Zoe of Byzantium elevates her adoptive son to the throne of the Eastern Roman Empire as Michael V "Non-Tech High Tech Litters the Landscape". USA Today. Retrieved on 2008-03-02. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 986 - Louis V becomes King of the Franks. 1127 - Assassination of Charles the Good
External links
- Silica gel mesh-metric conversions
- FDA Food Grade silica gel - U.S. National Institute of Health Uses in toothpaste and other ingested consumable products
- UK Material Safety Datasheet
- Silica Gel: DC Chemical Co., Ltd. Chemical properties
- Silica Gel with Moisture indicator: Instructions for Use Detailed use and re-drying info
- Silica Gel (Sodium Silicate): Chemical Data & Physical Data
- Silica Gel Dehumidifier FAQs Helpful Information on Rechargeable Silica Packs for Home Usage
Dictionary
silica gel
-noun
- (chemistry) a granular, porous form of silica made synthetically from sodium silicate and used as a desiccant.
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