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2014-01-04T16:09:05Z

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[[File:Einstein gyro gravity probe b.jpg|thumb|320px|right|A fused quartz sphere manufactured for use in a gyroscope in the [[Gravity Probe B]] experiment. It is one of the most accurate spheres ever manufactured, deviating from a perfect sphere by no more than 40 atoms of thickness. It is thought that only [[neutron star]]s are smoother.]]

'''Fused quartz''' or '''fused silica''' is [[glass]] consisting of [[Silicon dioxide|silica]] in [[amorphous solid|amorphous]] (non-[[crystal]]line) form. It differs from traditional [[Soda-lime glass|glasses]] in containing no other ingredients, which are typically added to glass to lower the melt temperature. Fused silica, therefore, has high working and melting temperatures. The optical and thermal properties of fused quartz are superior to those of other types of glass due to its purity. For these reasons, it finds use in situations such as [[semiconductor]] fabrication and laboratory equipment. It has better [[ultraviolet]] transmission than most other glasses, and so is used to make [[lens (optics)|lenses]] and other optics for the ultraviolet spectrum. Its low [[coefficient of thermal expansion]] also makes it a useful material for precision mirror substrates.<ref>{{cite journal|doi=10.1002/14356007.a12_365|chapter=Glass|title=Ullmann's Encyclopedia of Industrial Chemistry|year=2000|last1=De Jong|first1=Bernard H. W. S.|last2=Beerkens|first2=Ruud G. C.|last3=Van Nijnatten|first3=Peter A.|isbn=3-527-30673-0}}</ref> Fused quartz is a noncrystalline form of [[silicon dioxide]] ([[Silicon|Si]][[oxygen|O]]2). A common crystalline form of silicon dioxide is [[quartz]].

==Production==
===Feedstock===
''Fused quartz'' is produced by [[Melting|fusing]] (melting) high-purity silica sand, which consists of [[quartz]] crystals. Quartz contains only silicon and oxygen, although commercial quartz glass often contains impurities. The most dominant impurities are [[aluminium]] and [[titanium]].<ref>[http://www.heraeus-quarzglas.de/en/quarzglas/chemicalpurity/Chemical_purity.aspx ''Chemical purity of fused quartz / fused silica''], www.heraeus-quarzglas.com</ref>

===Fusion===
Melting is effected using at approximately 2000 °C using either an electrically heated furnace (electrically fused) or a gas/oxygen-fuelled furnace (flame fused). Fused silica can be made from almost any [[silicon]]-rich chemical precursor usually using a continuous flame [[hydrolysis]] process which involves chemical [[gasification]] of silicon, [[oxidation]] of this gas to silicon dioxide, and thermal fusion of the resulting dust (although there are alternative processes). This results in a transparent glass with an ultra-high purity and improved optical transmission in the deep [[ultraviolet]]. One common method involves adding [[silicon tetrachloride]] to a hydrogen–oxygen flame, however use of this precursor results in environmentally unfriendly by-products including [[chlorine]] and [[hydrochloric acid]]. To eliminate these by-products, new processes have been developed using an alternative feedstock, which has also resulted in a higher purity fused silica with further improved deep ultraviolet transmission.

===Product quality===
Fused quartz is normally transparent, the process of fusion results in a material that is translucent. The material can however appear opaque owing to the presence small air bubbles trapped within the material. The water content (and therefore infrared transmission of fused quartz and fused silica) is determined by the manufacturing process. Flame fused material always has a higher water content due to the combination of the hydrocarbons and oxygen fuelling the furnace forming [[hydroxyl]] [OH] groups within the material. An IR grade material typically has an [OH] content of <10 parts per million.

==Applications==
Most of the applications of fused silica exploit its wide transparency range, which extends from the UV to the near IR. Fused silica is the key starting material for [[optical fiber]], used for telecommunications.

Because of its strength and high melting point (compared to ordinary [[glass]]), fused silica is used as an envelope for [[halogen lamp]]s and [[high-intensity discharge lamp]]s, which must operate at a high envelope temperature to achieve their combination of high brightness and long life. Vacuum tubes with silica envelopes allowed for radiation-cooling by incandescent anodes.

The combination of strength, thermal stability, and UV transparency makes it an excellent substrate for projection masks for [[photolithography]].

[[File:EPROM Intel C1702A.jpg|thumb|An [[EPROM]] with fused quartz window in the top of the package]]
Its UV transparency also finds uses in the semiconductor industry; an [[EPROM]], or ''erasable programmable [[read only memory]]'', is a type of memory [[integrated circuit|chip]] that retains its data when its power supply is switched off, but which can be erased by exposure to strong [[ultraviolet]] light. EPROMs are recognizable by the transparent fused quartz window which sits on top of the package, through which the [[silicon]] chip is visible, and which permits exposure to [[UV light]] during erasing.

Due to the thermal stability and composition it is used in semiconductor fabrication furnaces.

Fused quartz has nearly ideal properties for fabricating [[first surface mirror]]s such as those used in [[telescope]]s. The material behaves in a predictable way and allows the optical fabricator to put a very smooth polish onto the surface and produce the desired figure with fewer testing iterations. In some instances, a high-purity UV grade of fused quartz has been used to make several of the individual uncoated lens elements of special purpose lenses including the Zeiss 105mm f/4.3 UV Sonnar, a lens formerly made for the Hasselblad camera, and the Nikon UV-Nikkor 105mm f/4.5 (presently sold as the Nikon PF10545MF-UV) lens. These lenses are used for UV photography, as the quartz glass has a lower extinction rate than lens made with more common [[Flint glass|flint]] or [[Crown glass (optics)|crown]] glass formulas.

===Refractory material applications===
Fused silica as an industrial raw material is used to make various refractory shapes such as crucibles, trays, shrouds, and rollers for many high-temperature thermal processes including [[steelmaking]], [[investment casting]], and glass manufacture. Refractory shapes made from fused silica have excellent thermal shock resistance and are chemically inert to most elements and compounds including virtually all acids, regardless of concentration, except [[hydrofluoric acid]] which is very reactive even in fairly low concentrations. Translucent fused silica tubes are commonly used to [[Quartz heater|sheathe electric elements in room heaters]], industrial furnaces and other similar applications.

Owing to its low mechanical damping at ordinary temperatures, it is used for [[Q factor|high-Q]] resonators, in particular, for [[Vibrating_structure_gyroscope#Wine_glass_resonator|wine-glass resonator]] of hemispherical resonator gyro (HRG).<ref>[http://www.sensorsmag.com/sensors/acceleration-vibration/an-overview-mems-inertial-sensing-technology-970 An Overview of MEMS Inertial Sensing Technology], February 1, 2003</ref><ref>{{cite journal|last1=Penn|first1=Steven D.|last2=Harry|first2=Gregory M.|last3=Gretarsson|first3=Andri M.|last4=Kittelberger|first4=Scott E.|last5=Saulson|first5=Peter R.|last6=Schiller|first6=John J.|last7=Smith|first7=Joshua R.|last8=Swords|first8=Sol O.|title=High quality factor measured in fused silica|journal=Review of Scientific Instruments|volume=72|issue=9|pages=3670|year=2001|doi=10.1063/1.1394183}}</ref>

Quartz glassware is occasionally used in chemistry laboratories when standard [[borosilicate glass]] cannot withstand high temperatures; it is more commonly found as a very basic element, such as a tube in a furnace, or as a flask, the elements in direct exposure to the heat.

==Physical properties==
The extremely low coefficient of thermal expansion, about 5.5×10−7/°C (20–320 °C), accounts for its remarkable ability to undergo large, rapid temperature changes without cracking (see [[thermal shock]]).

[[Image:Fused silica phosphorescence from a 24 million watt flash.jpg|thumb|300px|Phosphorescence in fused quartz from an extremely intense pulse of ultraviolet light, centered at 170 nm, in a flashtube.]]Fused quartz is prone to [[phosphorescence]] and "[[solarisation (physics)|solarisation]]" (purplish discoloration) under intense UV illumination, as is often seen in [[flashtube]]s. "UV grade" synthetic fused silica (sold under various tradenames including "HPFS", "Spectrosil" and "Suprasil") has a very low metallic impurity content making it transparent deeper into the [[ultraviolet light|ultraviolet]]. An optic with a thickness of 1 cm will have a transmittance of about 50% at a [[wavelength]] of 170 nm, which drops to only a few percent at 160 nm. However, its [[infrared]] transmission is limited by strong [[water absorption]]s at 2.2 μm and 2.7 μm.

"Infrared grade" fused quartz (tradenames "Infrasil", "Vitreosil IR" and others) which is electrically fused, has a greater presence of metallic impurities, limiting its UV transmittance wavelength to around 250 nm, but a much lower water content, leading to excellent infrared transmission up to 3.6 μm wavelength. All grades of transparent fused quartz/fused silica have nearly identical physical properties.

[[Image:Microflash-quartz-phosphorescence.jpg|thumb|250px| Phosphorescence of the quartz ignition tube of an [[air-gap flash]].]]

==Optical properties==
The [[Dispersion (optics)|optical dispersion]] of fused silica can be approximated by the following [[Sellmeier equation]]:<ref name=m>{{cite journal|last1=Malitson|first1=I. H.|title=Interspecimen Comparison of the Refractive Index of Fused Silica|journal=Journal of the Optical Society of America|volume=55|issue=10|pages=1205|year=1965|doi=10.1364/JOSA.55.001205}}</ref>

:<math>\varepsilon=n^2=1+\frac{0.69616630\lambda^2}{\lambda^2-0.0684043^2}+\frac{0.4079426\lambda^2}{\lambda^2-0.11624140^2}+\frac{0.8974794\lambda^2}{\lambda^2-9.896161^2},</math>
where the wavelength <math>\lambda</math> is measured in micrometers. This equation is valid between 0.21 and 3.71 micrometers and at 20 °C.<ref name=m/> Its validity was confirmed for wavelengths up to 6.7 <math>\mu</math>m.<ref name=rk>{{cite journal|last1=Kitamura|first1=R.|last2=Pilon|first2=L.|last3=Jonasz|first3=M.|title=Optical Constants of Silica Glass From Extreme Ultraviolet to Far Infrared at Near Room Temperatures|journal=Applied Optics|volume=46|issue=33|pages=8118–8133|year=2007|doi=10.1364/AO.46.008118}}</ref> Experimental data for the real (refractive index) and imaginary (absorption
index) parts of the complex refractive index of fused quartz reported in the literature over the spectral range from 30 nm to 1000 <math>\mu</math>m has been reviewed by Kitamura et al.<ref name=rk/> and are available [http://www.seas.ucla.edu/~pilon/downloads.htm online].

==Typical properties of clear fused silica==
*[[Density]]: 2.203 g/cm3
*[[Mohs scale of mineral hardness|Hardness]]: 5.3–6.5 ([[Mohs scale of mineral hardness|Mohs scale]]), 8.8 [[Pascal (unit)|GPa]]
*[[Ultimate tensile strength|Tensile strength]]: 48.3 [[Pascal (unit)|MPa]]
*[[Compressive strength]]: >1.1 [[Pascal (unit)|GPa]]
*[[Bulk modulus]]: ~37 GPa
*[[Shear modulus|Rigidity modulus]]: 31 GPa
*[[Young's modulus]]: 71.7 GPa
*[[Poisson's ratio]]: 0.17
*[[Lamé parameters|Lame elastic constants]]: λ=15.87 GPa, μ=31.26 GPa
*[[Thermal expansion#Coefficient of thermal expansion|Coefficient of thermal expansion]]: 5.5×10−7/°C (average from 20 °C to 320 °C)
*[[Thermal conductivity]]: 1.3 W/(m·K)
*[[Heat capacity#Extensive and intensive quantities|Specific heat capacity]]: 45.3 J/(mol·K)
*[[Softening point]]: c. 1665 °C
*[[Annealing (glass)|Annealing point]]: c. 1140 °C
*[[Annealing (glass)|Strain point]]: 1070 °C
*[[Electrical resistivity and conductivity|Electrical resistivity]]: >1018 Ω·m
*[[Relative permittivity|Dielectric constant]]: 3.75 at 20 °C 1 MHz
*[[Propagation constant#Attenuation constant|Dielectric loss factor]]: less than 0.0004 at 20 °C 1 MHz
*[[Refractive index|Index of refraction]]: at 587.6 nm (''n''d): 1.4585
*Change of refractive index with temperature (0 to 700 °C): 1.28×10−5/°C (between 20 and 30 °C)<ref name="m"/>
*[[Strain-optic coefficients]]: p11=0.113, p12=0.252.
*[[Hamaker constant]]: A=6.5×10-20 J.
*[[Dielectric strength]]: 250–400 kV/cm at 20 °C<ref>[http://www.sciner.com/Opticsland/FS.htm Fused silica datapage]</ref>

==See also==
*[[Vycor]]
*[[Structure of liquids and glasses]]

==References==
{{Reflist|2}}

==External links==
* [http://books.google.com/books?id=4OIDAAAAMBAJ&pg=-PA97&dq=Popular+Science+1930+plane+%22Popular+Mechanics%22&hl=en&ei=NCt4TtDKIqnf0QG65_3-Cw&sa=X&oi=book_result&ct=book-thumbnail&resnum=6&ved=0CEIQ6wEwBTge#v=onepage&q&f=true "Frozen Eye to Bring New Worlds into View" ''Popular Mechanics'', June 1931] General Electrics, West Lynn Massachusetts Labs work on large fuzed quartz blocks

{{Glass science}}

{{DEFAULTSORT:Fused Quartz}}
[[Category:Glass types]]
[[Category:Low-expansion glass]]
[[Category:Chemical engineering]]
[[Category:Glass compositions]]
[[Category:Silicon dioxide]]
[[Category:Transparent materials]]
[[Category:Quartz varieties]]

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2012-12-10T13:57:16Z

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