Silicon carbide
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225202032
2008-07-12T12:53:30Z
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/* Semiconductor */ reference
{{Chembox new
| Name = Silicon carbide
| ImageFile = Silicon-carbide-3D-balls.png
| ImageSize = 140px
| ImageName = Ball-and-stick model of part of a crystal of SiC
| ImageFile1 = silicon carbide detail.jpg
| ImageSize1 = 140px
| OtherNames =
| Section1 = {{Chembox Identifiers
| CASNo = 409-21-2
}}
| Section2 = {{Chembox Properties
| Formula = SiC
| MolarMass = 40.097 g/mol
| Appearance = black-green odorless powder
| Density = 3.22 g/cm³, solid
| Solubility = insoluble
| MeltingPt = 2730°C
| BoilingPt =
}}
| Section7 = {{Chembox Hazards
| EUClass = not listed
| NFPA-H = 1
| NFPA-F =
| NFPA-R =
}}
}}
'''Silicon carbide''' ({{Silicon}}{{Carbon}}) is a [[Chemical compound|compound]] of [[silicon]] and [[carbon]] bonded together to form [[ceramic]]s, but it also occurs in nature as the extremely rare mineral [[moissanite]].
==Production==
Due to the rarity of natural moissanite, silicon carbide is typically man-made. Most often it is used as an [[abrasive]]. More recently as a [[semiconductor]] and [[diamond simulant]] of gem quality. The simplest manufacturing process is to combine [[silica]] [[sand]] and [[carbon]] in an Acheson graphite electric resistance furnace at a high temperature, between 1600 and 2500 °C.
The material formed in the Acheson furnace varies in purity, according to its distance from the [[graphite]] [[resistor]] [[heating element|heat source]]. Colorless, pale yellow and green crystals have the highest purity and are found closest to the resistor. The color changes to blue and black at greater distance from the resistor, and these darker crystals are less pure. Nitrogen and aluminium are common impurities, and they affect the electrical conductivity of SiC.
Purer silicon carbide can be made by the more expensive process of [[chemical vapor deposition]] (CVD). Commercial large [[single crystal]] silicon carbide is grown using a [[physical vapor deposition|physical vapor transport]] method commonly known as modified [[Lely method]].
Purer silicon carbide can also be prepared by the [[thermal decomposition]] of a polymer, [[poly (methylsilyne)]], under an [[inert atmosphere]] at low temperatures. Relative to the CVD process, the pyrolysis method is advantageous because the polymer can be formed into various shapes prior to thermalization into the ceramic.
==Discovery==
[[Image:SiC p1390066.jpg|thumb|Silicon carbide [[single crystal]] from one of the [[Minatec]] laboratories]]
The material was manufactured by [[Edward Goodrich Acheson]] around 1893, and he not only developed the electric batch [[furnace]] by which SiC is still made today but also formed The Carborundum Company to manufacture it in bulk, initially for use as an abrasive. In 1900 the company settled with the [[Electric Smelting and Aluminum Company]] when a judges' decision gave "priority broadly" to its founders "for reducing ores and other substances by the incandescent method".<ref>{{cite journal|author=Mabery, Charles F.|title=Notes, On Carborundum|pages=706–707|url=http://books.google.com/books?id=fBIDAAAAYAAJ&pg=PA706|date=1900|volume=XXII|issue=Part II|journal=Journal of the American Chemical Society|publisher=Johnson Reprint Company, via Google Books scan of Harvard University copy|accessdate=2007-10-28}}</ref> It is said that Acheson was trying to dissolve carbon in molten [[corundum]] ([[alumina]]) and discovered the presence of hard, blue-black crystals which he believed to be a compound of carbon and corundum: hence carborundum. Or, he named the material "carborundum" by analogy to [[corundum]], which is another very hard substance (9 on the [[Mohs scale]]).
===In nature===
Naturally occurring '''moissanite''' is found only in minute quantities in certain types of meteorite and in [[corundum]] deposits and [[kimberlite]]. Virtually all of the silicon carbide sold in the world, including moissanite jewels, is [[chemical synthesis|synthetic]]. Natural moissanite was first found in 1893 as a small component of the [[Canyon Diablo meteorite]] in [[Arizona]] by Dr. [[Henri Moissan|Ferdinand Henri Moissan]], after whom the material was named in 1905. Moissan's discovery of naturally occurring SiC was initially disputed because his sample may have been contaminated by silicon carbide [[saw blade]]s that were already on the market at that time.
Analysis of SiC grains found in the Murchison carbonaceous chondrite meteorite has revealed anomalous isotopic ratios of carbon and silicon, indicating an origin from outside the solar system.<ref>[http://img.chem.ucl.ac.uk/www/kelly/history.htm http://img.chem.ucl.ac.uk/www/kelly/history.htm]</ref> 99% of these SiC grains originate around carbon-rich [[Asymptotic Giant Branch]] stars. SiC is commonly found around these stars as deduced from their infrared spectra.
==Properties==
Silicon carbide exists in at least 70 crystalline forms. Alpha silicon carbide (α-SiC) is the most commonly encountered [[Polymorphism (materials science)|polymorph]]; it is formed at temperatures greater than 2000 °C and has a [[hexagonal (crystal system)|hexagonal]] [[crystal structure]] (similar to [[Wurtzite]]). The beta modification (β-SiC), with a [[face-centered cubic]] crystal structure (similar to [[diamond cubic|diamond]] and [[zincblende]] or [[sphalerite]]), is formed at temperatures below 2000 °C and is shown in the structure at the top of the page. Until recently, the beta form has had relatively few commercial uses, although there is now increasing interest in its use as a support for heterogeneous catalysts, owing to its higher surface area compared to the alpha form.
Silicon carbide has a specific gravity of 3.2, and its high sublimation temperature (approximately 2700 °C) makes it useful for [[bearing (mechanical)|bearings]] and furnace parts. Silicon carbide does not melt at any known pressure. It is also highly inert chemically. There is currently much interest in its use as a [[semiconductor material]] in electronics, where its high [[thermal conductivity]], high [[electric field]] breakdown strength and high maximum [[Current (electricity)|current]] density make it more promising than silicon for high-powered devices.<ref>http://www.mdatechnology.net/techsearch.asp?articleid=174[http://www.mdatechnology.net/techsearch.asp?articleid=174]</ref> In addition, it has strong coupling to [[microwave]] radiation, which together with its high sublimation point, permits practical use in heating and casting metals. SiC also has a very low [[coefficient of thermal expansion]] and experiences no [[phase transition]]s that would cause discontinuities in thermal expansion.
Pure SiC is colorless. The brown to black color of industrial product results from [[iron]] impurities. The rainbow-like lustre of the crystals is caused by a [[passivation layer]] of [[silicon dioxide]] that forms on the surface.
==Uses==
===Semiconductor===
Pure α-SiC is an [[intrinsic semiconductor]] with [[band gap]]s of 3.28 eV (4H) and 3.03 eV (6H) respectively.<ref>http://www.ioffe.ru/SVA/NSM/Semicond/SiC/bandstr.html#Basic</ref>
====Lightning arrestors====
The earliest electrical application of SiC was in [[lightning arrester]]s in electric power systems. These devices must exhibit high [[electrical resistance|resistance]] until the [[voltage]] across them reaches a certain threshold ''V<sub>T</sub>'', at which point their resistance must drop to a lower level and maintain this level until the applied voltage drops below ''V<sub>T</sub>''.
It was recognized early on that SiC had such a voltage-dependent resistance, and so columns of SiC pellets were connected between high-voltage [[electric power transmission|power line]]s and the earth. When a [[lightning strike]] to the line raises the line voltage sufficiently, the SiC column will conduct, allowing strike current to pass harmlessly to the earth instead of along the power line. Such SiC columns proved to conduct significantly at normal power-line operating voltages and thus had to be placed [[Series and parallel circuits|in series]] with a [[spark gap]]. This spark gap is [[ion]]ized and rendered conductive when lightning raises the voltage of the power line conductor, thus effectively connecting the SiC column between the power conductor and the earth. Spark gaps used in lightning arrestors are unreliable, either failing to strike an arc when needed or failing to turn off afterwards, in the latter case due to material failure or contamination by dust or salt. Usages of SiC columns was originally intended as a way to eliminate the need for the spark gap in a lightning arrester. Gapped SiC lightning arresters were used as lightning-protection tool and sold under [[GE]] and [[Westinghouse Electric Corporation (1886)|Westinghouse]] brand names, among others. The gapped SiC arrester has been largely displaced by no-gap [[varistors]] that use columns of [[zinc oxide]] pellets.
====Circuit elements====
Silicon carbide is used for blue [[Light-emitting diode|LED]]s, ultrafast, high-voltage [[Schottky diode]]s, [[MOSFET]]s and high temperature [[thyristors]] for high-power switching. A paper by Jayan Baliga<ref>{{ cite journal | last=Bhatnagar | first=M. | coauthors=Baliga, B.J. | url=http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel1/16/5182/00199372.pdf?tp=&isnumber=5182&arnumber=199372 | title=Comparison of 6H-SiC, 3C-SiC, and Si for power devices | journal=IEEE Transactions on Electron Devices | month=March | year=1993 | volume=40 | issue=3 | pages=645–655 | doi=10.1109/16.199372 }}</ref> demonstrated the potential of SiC as a power device material.
Currently, problems with the interface of SiC with [[silicon dioxide]] has hampered the development of SiC based power MOSFET and IGBTs.{{Fact|date=June 2008}} Another problem is that SiC itself breaks down at high electric fields due to the formation of extended stacking faults, but this problem may have been resolved relatively recently.<ref>{{ cite journal | url=http://www.nature.com/nature/journal/v430/n7003/full/430974a.html | last=Madar | first=Roland | title=Materials science: Silicon carbide in contention | journal=Nature | issue=430 | pages=974–975 | date=2004-08-26 | accessdate=2008-06-06 | doi=10.1038/430974a | volume=430 }}</ref>
====High-temperature applications====
Due to its high [[thermal conductivity]], SiC is also used as substrate for other semiconductor materials such as [[gallium nitride]]. Due to its wide [[band gap]], SiC-based parts are capable of operating at high temperature (over 350 °C), which together with good [[thermal conductivity]] of SiC makes SiC devices good candidates for elevated temperature applications. SiC devices also possess increased tolerance to [[radiation hardening|radiation damage]], making SiC a desirable material for defense and aerospace applications. Gallium nitride is itself also an alternative material in many applications. Although [[diamond]] has an even higher band gap, SiC-based devices are easier to manufacture because is is more convenient to grow an insulating layer of [[silicon dioxide]] on the surface of a silicon carbide wafer than it is on diamond.
Pure SiC is a poor [[electrical conductor]]. Addition of suitable [[dopant]]s significantly enhances its conductivity. Typically, such material has a negative temperature coefficient between room temperature and about 900 °C, and [[positive temperature coefficient]] at higher temperatures, making it suitable material for high temperature [[heating element]]s.
====Ultraviolet detector====
Silicon carbide is also used as an [[ultraviolet]] detector. [[Nikola Tesla]], around the turn of the 20th century, performed a variety of experiments with carborundum. [[Electroluminescence]] of silicon carbide was observed by Captain [[Henry Joseph Round]] in 1907 and by [[Oleg Losev|O. V. Losev]] in the [[Soviet Union]] in 1923.<ref name="ultraviolet">{{ cite web | url=http://www.indiana.edu/~hightech/fpd/papers/ELDs.html | title=A History of Electroluminescent Displays | last=Hart | first=Jeffrey A. | coauthors=Stefanie Ann Lenway, Thomas Murtha }}</ref>
===Structural material===
In the 1980s and 1990s, silicon carbide was studied on several research programs for high-temperature gas turbines in the [[United States]], [[Japan]], and [[Europe]]. The components were intended to replace [[nickel]] [[superalloy]] [[turbine]] blades or nozzle vanes. However, none of these projects resulted in a production quantity, mainly because of its low impact resistance and its low fracture [[toughness]].
===Astronomy===
Silicon carbide's hardness and rigidity make it a desirable [[mirror]] material for [[astronomy|astronomical]] work, although its properties also make manufacturing and designing such mirrors quite difficult.
While rare on Earth, silicon carbide is remarkably common in space. It is a common form of stardust found around carbon-rich stars, and examples of this stardust have been found in pristine condition in primitive (unaltered) meteorites. The silicon carbide found in space and in meteorites is almost exclusively the beta-polymorph.
Silicon carbide may be a major component of the mantles of as-yet hypothetical [[carbon planet]]s.
===Abrasive===
In the arts, silicon carbide is a popular [[abrasive]] in modern [[lapidary]] due to the durability and low cost of the material.
In manufacturing, it is used for its hardness in [[abrasive machining]] processes such as [[grinding]], [[Honing (metalworking)|honing]], and [[water-jet cutting]].
Particles of silicon carbide are laminated to paper to create [[sandpaper]]s and the grip tape on [[skateboard]]s.
===Disc brake===
Silicon-infiltrated [[Carbon-carbon|carbon-carbon composite]] is used for high performance [[disc brake|brake discs]] as it is able to withstand extreme temperatures. The silicon reacts with the graphite in the carbon-carbon composite to become silicon carbide. These discs are used on some sports cars, including the [[Porsche Carrera GT]].
===Clutch===
[[Porsche Carrera GT]]
===Diesel particulate filter===
Silicon carbide is used in a [[sinter]]ed form for [[diesel particulate filter]]s.
===Thin filament pyrometry===
Silicon carbide fibers are used to measure gas temperatures in a diagnostic technique called [[thin filament pyrometry]].
===Ceramic membrane===
Silicon carbide is used for producing ceramic membranes for industrial processes, yielding high fluxes due to the sintering process.
===Cutting tools===
In 1982 at the [[Oak Ridge National Laboratory|Oak Ridge National Laboratories]], [[George Wei]], [[Terry Tiegs]], and [[Paul Becher]] discovered a composite of [[aluminium oxide]] and silicon carbide [[whisker (metallurgy)|whiskers]]. This material proved to be exceptionally strong. Development of this laboratory-produced composite to a commercial product took only three years. In 1985, the first commercial cutting tools made from this alumina and silicon carbide whisker-reinforced composite were introduced by the Advanced Composite Materials Corporation (ACMC) and Greenleaf Corporation.
===Heating element===
References to silicon carbide [[heating element]]s exist from the early 20th century when they were produced by Acheson's Carborundum Co. in the U.S. and EKL in Berlin. Silicon carbide offered increased operating temperatures compared with metallic heaters, although the operating temperature was limited initially by the water-cooled terminals, which brought the electric current to the silicon carbide hot zone. The terminals were not attached to the hot zone, but were held in place by weights, or springs. Operating temperature and efficiency was later increased by the use of separate low resistance silicon carbide "cold ends", usually of a larger diameter than the hot zone, but still held in place only by mechanical pressure. The development of reaction-bonding techniques led to the introduction of jointed elements. Initially, these featured larger diameter cold ends, but by the 1940s, equal diameter elements were being produced. From the 1960s onwards, one-piece elements were produced, with cold ends created by filling the pore volume with a silicon alloy. Another one-piece technique is to cut a spiral slot in a homogeneous tube where the hot section is desired. Further developments have included the production of multi-leg elements, where two or more legs are joined to a common bridge, and the production of high density, reaction-bonded elements, which provide additional resistance to [[oxidation]] and chemical attack.
Silicon carbide elements are used today in the melting of non-ferrous metals and glasses, [[heat treatment]] of metals, [[float glass]] production, production of ceramics and electronics components, etc.
===Nuclear fuel===
Silicon carbide is often used as a layer of the [[TRISO]] coating for the [[nuclear fuel]] elements of [[high temperature gas cooled reactor]]s or [[very high temperature reactor]]s such as the [[Pebble Bed Reactor]].
===Jewelry===
As a [[Gemstone]] used in [[jewellery|jewelry]], silicon carbide is called '''Moissanite''' after the jewel's discoverer Dr. [[Henri Moissan]]<ref name="http://shopping.schubachstore.com/site/hosted-MOISSANITE-EDUCATION.htm">[http://shopping.schubachstore.com/site/hosted-MOISSANITE-EDUCATION.htm Moissanite Education]</ref>. Moissanite is similar to [[diamond]] in several important respects: it is transparent and hard (9, although a patent states 8.5-9.0,<ref>Patent #5,762,896 [http://v3.espacenet.com/textdoc?DB=EPODOC&IDX=US5762896&F=0 Espacenet record]</ref><!--before you change 9.25 into 9, read the note, this is the number used in the reference, even though it may not be correct according to Moh's scale--><ref>Most in the jewelry industry may not recognize the 1/4 fractional intervals on the Mohs scale (a relative scale), and it is technically not correct since the Mohs scale only contains whole and half numbers. But the issuers of the patent use it in showing exactly where certain minerals are in relation to each other. On the original Mohs scale diamond was listed as a 10 and sapphire is listed as a 9. On an absolute scale, a diamonds hardness is between 5700–10400 on the Knoop scale, while a sapphire's hardness is 2000. The Knoop hardness of moissanite is 3000. This puts the Mohs hardness of moissanite around 8.5–9.25—as stated here, 9 1/4 may not be recognized, but 8.5–9.25 is the number used in the patents.</ref> on the [[Mohs scale of mineral hardness|Mohs scale]] compared to 10 for diamond), with a [[refractive index]] between 2.65 and 2.69 (compared to 2.42 for diamond). Moissanite is somewhat harder than common [[cubic zirconia]]. Unlike diamond, Moissanite is strongly [[birefringent]]. This quality is desirable in some optical applications, but not in gemstones. For this reason, Moissanite jewels are cut along the [[optic axis]] of the crystal to minimize birefringent effects. It is lighter (density 3.22 vs. 3.56), and much more resistant to heat. This results in a stone of higher [[Lustre (mineralogy)|lustre]], sharper facets and good resilience. Loose moissanite stones may be placed directly into ring moulds; unlike diamond, which burns at 800 °C, moissanite remains undamaged by temperatures up to twice the 900 °C melting point of [[carat (purity)|18k]] [[gold]].
Moissanite has become popular as a diamond substitute, and may be misidentified as diamond, since its [[thermal conductivity]] is much closer to that of diamond than any other diamond substitutes. It can be distinguished from diamond by its [[birefringence]] and a very slight green, yellow, or gray fluorescence under ultraviolet light.
===Steel===
[[Image:Silicon carbide chunk.jpg|thumb|300px|right|Piece of silicon carbide used in steel making]]
Silicon carbide dissolved in a [[basic oxygen furnace]] used for making [[steel]] acts as a [[fuel]] and provides energy which increases the scrap to hot metal ratio.<ref name="http://www.millerandco.com/products/briquettes_steel/">[http://www.millerandco.com/products/briquettes_steel/ http://www.millerandco.com/products/briquettes_steel/]</ref> It can also be used to raise tap temperatures and adjust the carbon content.
90% silicon carbide is used by the steel industry as a [[ladle (metallurgy)|ladle]] [[deoxidizer]],
a source of [[silicon]] and [[carbon]] in the [[Ladle (metallurgy)|ladle]], an [[electric furnace]] [[slag]] deoxidizer, and as a synthetic slag additive.<ref name="http://www.millerandco.com/products/briquettes_steel/specifications/briq90.htm">[http://www.millerandco.com/products/briquettes_steel/specifications/briq90.htm http://www.millerandco.com/products/briquettes_steel/specifications/briq90.htm]</ref> According to Miller and Company,<ref name="http://www.millerandco.com/">[http://www.millerandco.com/ Miller and Company]</ref> it costs less than [[ferrosilicon]] and [[carbon]] combination, produces cleaner steel due to low level of [[trace element]]s, it has a low gas content, it does not lower the temperature of steel, and it has an abundant world wide supply. The silicon carbide used as a steel additive or fuel comes as a granular product in either bulk and bags.
50% and 65% silicon carbide are used in the [[steel industry]] for processing steel and iron scrap. Typically supplied as [[Cinder block|blocks]] and made from silicon carbide crucible scrap, it helps extend the hot metal supply and raises the tap temperature.<ref name="http://www.millerandco.com/products/briquettes_steel/specifications/briq65.htm">[http://www.millerandco.com/products/briquettes_steel/specifications/briq65.htm http://www.millerandco.com/products/briquettes_steel/specifications/briq65.htm]</ref> The [[Cinder block|blocks]] are typically made using an automated [[concrete block]] making machine, and utilize [[water]] and [[limestone]] [[cement]] as a binder.
===Armour===
Like other hard ceramics (namely [[alumina]] and [[boron carbide]]), silicon carbide is used in [[composite armour]] (eg. [[Chobham armour]]), and in [[ceramic plate]]s in [[bulletproof vest]]s. [[Dragon Skin body armor|Dragon Skin]], which is produced by [[Pinnacle Armor]], utilizes disks of silicon carbide. It is light weight, flexible, and rifle round resistant, making it suitable for use on the front lines of battle.
===Catalyst support===
The natural resistance to oxidation exhibited by silicon carbide, as well as the discovery of new ways to synthesize the higher surface area beta form, has led to significant interest in its use as a heterogeneous catalyst support. The beta cubic form has already been employed for several years as a catalyst support for the oxidation of C4 hydrocarbons, such as n-butane, to maleic anhydride.
==In popular culture==
* In [[Edgar Rice Burroughs]]' [[Barsoom]] series, "carborundum" is used as building material for city walls.
* In [[2001: A Space Odyssey (novel)|2001: A Space Odyssey]] by [[Arthur C. Clarke]] (and the related series of books and films) the [[The Monolith|monolith]]s (or at least their exteriors) were made of silicon carbide
* In the ''[[Discworld]]'' novel ''[[Monstrous Regiment (novel)|Monstrous Regiment]]'': Carborundum is the name of the Troll that enlists.
* In the movie [[Snatch (film)|Snatch]], a pawn shop employee (Sol) determines a diamond is actually Moissanite, much to the dismay of the thief (Bad Boy Lincoln) who stole the ring.
* The name of the material is part of the pun "[[Illegitimi non carborundum]]" ([[Dog Latin]] for "don't let the bastards grind you down"), which figures into a football fight song of [[Harvard University]] among other things.
* In the BBC television show ''[[Top Gear (current format)|Top Gear]]'', host [[Jeremy Clarkson]] expresses excitement over the mere mention of silicon carbide used in the brakes and clutch of the Porsche Carrera GT.
* Silicon carbide is the material used for the [[National Design Awards]] trophy, awarded by the [[Cooper-Hewitt National Design Museum]] designed by [[William Drenttel]] and [[Jessica Helfand]] and manufactured by Norton Electronics.
==Patents and trademarks==
Edward Goodrich Acheson (1856–1931) patented the method for making silicon carbide powder on [[February 28]], [[1893]]. On [[May 19]], [[1896]], he was also issued a patent for an electrical furnace used to produce silicon carbide.<ref>{{US patent|492767}} -- ''Production of artificial crystalline carbonaceous material''</ref> Carborundum is a trademark of [[Saint-Gobain]] Abrasives.
==See also==
* [[Diamond simulant]]
* [[Illegitimi non carborundum]], mock-Latin using the trademark Carborundum as if it were a [[Latin]] verb [[gerund]].
==Notes and references==
{{reflist}}
==External links==
* [http://www.moissanite-buyers-guide.com Moissanite Buyer's Guide] How to buy moissanite jewelry.
* [http://img.chem.ucl.ac.uk/www/kelly/moissanite.htm A Brief History of Silicon Carbide] Dr J F Kelly, University of London
* [http://physchem.ox.ac.uk/MSDS/SI/silicon_carbide.html Material Safety Data Sheet] for Silicon Carbide
* [http://www.mindat.org/min-2743.html Mindat.org]
* [http://www.farlang.com/gemstones/us-geol-survey-1905/page_040 discovery of Moissanite by Moissan] Moissan studied Meteorites. George Frederick Kunz describes this discovery in USGS annual report.
[[Category:Carbides]]
[[Category:Silicon compounds]]
[[Category:Semiconductor materials]]
[[Category:Superhard materials]]
[[Category:Ceramic materials]]
[[Category:Refractory materials]]
[[Category:Gemstones]]
[[Category:Synthetic minerals]]
[[Category:Deoxidizers]]
[[cs:Karborundum]]
[[de:Siliciumcarbid]]
[[et:Ränikarbiid]]
[[es:Carburo de silicio]]
[[fa:سیلیسیم کاربید]]
[[fr:Carbure de silicium]]
[[it:Moissanite]]
[[nl:Siliciumcarbide]]
[[ja:炭化ケイ素]]
[[no:Silisiumkarbid]]
[[pl:Węglik krzemu]]
[[ru:Карбид кремния]]
[[sk:Karborundum]]
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