Fused quartz - AbsoluteAstronomy.com

Fused quartz and fused silica are types of glass

Glass

Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...

containing primarily silica

Silicon dioxide

The chemical compound silicon dioxide, also known as silica , is an oxide of silicon with the chemical formula '. It has been known for its hardness since antiquity...

in amorphous

Amorphous solid

In condensed matter physics, an amorphous or non-crystalline solid is a solid that lacks the long-range order characteristic of a crystal....

(non-crystal

Crystal

A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...

line) form. They are manufactured using several different processes. Note that glasses formed by the traditional 'melt–quench' methods (heating the material to melting temperatures, then rapidly cooling to the solid glass phase), are often referred to as 'vitreous', as in 'vitreous silica'. The term 'vitreous' is synonymous with 'glass', when used in the melt–quench context.

Fused quartz is manufactured by melting naturally occurring quartz

Quartz

Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...

crystals of high purity at approximately 2000 °C, using either an electrically heated furnace (electrically fused) or a gas/oxygen-fuelled furnace (flame fused). Fused quartz is normally transparent. 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

Semiconductor

A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...

fabrication and laboratory equipment. It has better ultraviolet

Ultraviolet

Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

transmission than most other glasses, and so is used to make lenses

Lens (optics)

A lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam. A simple lens consists of a single optical element...

and other optics for the ultraviolet spectrum. Its low coefficient of thermal expansion also makes it a useful material for precision mirror substrates.

Fused quartz can also form naturally. The naturally occurring form is a metamorphic rock

Metamorphic rock

Metamorphic rock is the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change...

known as quartzite

Quartzite

Quartzite is a hard metamorphic rock which was originally sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to gray, though quartzites often occur in various shades of pink...

. An increase in pressure and temperature causes the quartz crystals within the rock to fuse together. An important distinction is that the quartz in quartzite is not an amorphous form.

Fused silica is produced using high-purity silica sand as the feedstock, and is normally melted using an electric furnace, resulting in a material that is translucent or opaque. (This opacity is caused by very small air bubbles trapped within the material.)

Synthetic fused silica is made from a silicon

Silicon

Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

-rich chemical precursor usually using a continuous flame hydrolysis

Hydrolysis

Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...

process which involves chemical gasification

Gasification

Gasification is a process that converts organic or fossil based carbonaceous materials into carbon monoxide, hydrogen, carbon dioxide and methane. This is achieved by reacting the material at high temperatures , without combustion, with a controlled amount of oxygen and/or steam...

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

Ultraviolet

Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

. One common method involves adding silicon tetrachloride

Silicon tetrachloride

Silicon tetrachloride is the inorganic compound with the formula SiCl4. It is a colourless volatile liquid that fumes in air. It is used to produce high purity silicon and silica for commercial applications.-Preparation:...

to a hydrogen–oxygen flame, however use of this precursor results in environmentally unfriendly by-products including chlorine

Chlorine

Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

and hydrochloric acid

Hydrochloric acid

Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric 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.

Fumed silica
Fumed silica
Fumed silica, also known as pyrogenic silica because it is produced in a flame, consists of microscopic droplets of amorphous silica fused into branched, chainlike, three-dimensional secondary particles which then agglomerate into tertiary particles. The resulting powder has an extremely low bulk...

is manufactured by a similar flame hydrolysis process to synthetic fused silica, however it is in the form of a fine powder/dust and is typically used in applications such as fillers for rubbers and plastics, coatings, adhesives, cements, sealants, cosmetics, pharmaceuticals, inks and abrasives.

Chemistry

Fused quartz is a noncrystalline form of silicon dioxide

Silicon dioxide

The chemical compound silicon dioxide, also known as silica , is an oxide of silicon with the chemical formula '. It has been known for its hardness since antiquity...

(Si

Silicon

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

₂), which is also called silica. (The crystalline form of this material is quartz

Quartz

). Though quartz glass in theory contains only silicon and oxygen, industrially produced quartz glass / fused silica contains impurities. The typical impurities depend on the starting material and the process used. The most dominant impurities are aluminium

Aluminium

Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

and titanium

Titanium

Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....

.

Quartz has a high melting point because many strong covalent bonds have to be broken.

Applications

Specially prepared fused silica is the key starting material used to make optical fiber

Optical fiber

An optical fiber is a flexible, transparent fiber made of a pure glass not much wider than a human hair. It functions as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of...

for telecommunications.

Because of its strength and high melting point (compared to ordinary glass

Glass

), fused silica is used as an envelope for halogen lamp

Halogen lamp

A halogen lamp, also known as a tungsten halogen lamp, is an incandescent lamp with a tungsten filament contained within an inert gas and a small amount of a halogen such as iodine or bromine. The chemical halogen cycle redeposits evaporated tungsten back on to the filament, extending the life of...

s, which must operate at a high envelope temperature to achieve their combination of high brightness and long life.

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

Photolithography

Photolithography is a process used in microfabrication to selectively remove parts of a thin film or the bulk of a substrate. It uses light to transfer a geometric pattern from a photomask to a light-sensitive chemical "photoresist", or simply "resist," on the substrate...

Its UV transparency also finds uses in the semiconductor industry; an EPROM

EPROM

An EPROM , or erasable programmable read only memory, is a type of memory chip that retains its data when its power supply is switched off. In other words, it is non-volatile. It is an array of floating-gate transistors individually programmed by an electronic device that supplies higher voltages...

, or erasable programmable read only memory, is a type of memory chip

Integrated circuit

An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...

that retains its data when its power supply is switched off, but which can be erased by exposure to strong ultraviolet

Ultraviolet

Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

light. EPROMs are recognizable by the transparent fused quartz window which sits on top of the package, through which the silicon

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 mirrors such as those used in telescope

Telescope

A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...

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

Flint glass

Flint glass is optical glass that has relatively high refractive index and low Abbe number. Flint glasses are arbitrarily defined as having an Abbe number of 50 to 55 or less. The currently known flint glasses have refractive indices ranging between 1.45 and 2.00...

or crown

Crown glass (optics)

Crown glass is type of optical glass used in lenses and other optical components. It has relatively low refractive index and low dispersion...

glass formulas.

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

Steelmaking

Steelmaking is the second step in producing steel from iron ore. In this stage, impurities such as sulfur, phosphorus, and excess carbon are removed from the raw iron, and alloying elements such as manganese, nickel, chromium and vanadium are added to produce the exact steel required.-Older...

, investment casting

Investment casting

Investment casting is an industrial process based on and also called lost-wax casting, one of the oldest known metal-forming techniques. From 5,000 years ago, when beeswax formed the pattern, to today’s high-technology waxes, refractory materials and specialist alloys, the castings allow the...

, 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

Hydrofluoric acid

Hydrofluoric acid is a solution of hydrogen fluoride in water. It is a valued source of fluorine and is the precursor to numerous pharmaceuticals such as fluoxetine and diverse materials such as PTFE ....

which is very reactive even in fairly low concentrations. Translucent fused silica tubes are commonly used to sheathe electric elements in room heaters, industrial furnaces and other similar applications.

Thanks to its low mechanical damping at ordinary temperatures, it is used for high-Q

Q factor

In physics and engineering the quality factor or Q factor is a dimensionless parameter that describes how under-damped an oscillator or resonator is, or equivalently, characterizes a resonator's bandwidth relative to its center frequency....

resonators, in particular, for wine-glass resonator of hemispherical resonator gyro (HRG).

Quartz glassware is occasionally used in chemistry laboratories when standard borosillicate glass can not 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

Thermal shock

Thermal shock is the name given to cracking as a result of rapid temperature change. Glass and ceramic objects are particularly vulnerable to this form of failure, due to their low toughness, low thermal conductivity, and high thermal expansion coefficients...

).

Fused quartz is prone to phosphorescence

Phosphorescence

Phosphorescence is a specific type of photoluminescence related to fluorescence. Unlike fluorescence, a phosphorescent material does not immediately re-emit the radiation it absorbs. The slower time scales of the re-emission are associated with "forbidden" energy state transitions in quantum...

and "solarisation" (purplish discoloration) under intense UV illumination, as is often seen in flashtube

Flashtube

A flashtube, also called a flashlamp, is an electric arc lamp designed to produce extremely intense, incoherent, full-spectrum white light for very short durations. Flashtubes are made of a length of glass tubing with electrodes at either end and are filled with a gas that, when triggered, ionizes...

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. An optic with a thickness of 1 cm will have a transmittance of about 50% at a wavelength

Wavelength

In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...

of 170 nm, which drops to only a few percent at 160 nm. However, its infrared

Infrared

Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

transmission is limited by strong water absorption

Water absorption

During the transmission of electromagnetic radiation through a medium containing water molecules, portions of the electromagnetic spectrum are absorbed by water molecules...

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.

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

Hydroxyl

A hydroxyl is a chemical group containing an oxygen atom covalently bonded with a hydrogen atom. In inorganic chemistry, the hydroxyl group is known as the hydroxide ion, and scientists and reference works generally use these different terms though they refer to the same chemical structure in...

[OH] groups within the material. An IR grade material typically has an [OH] content of <10 parts per million.

Typical properties of clear fused silica

Density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...

: 2.203 g/cm³
Hardness
Mohs scale of mineral hardness
The Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. It was created in 1812 by the German geologist and mineralogist Friedrich Mohs and is one of several definitions of hardness in...

: 5.3–6.5 (Mohs scale
Mohs scale of mineral hardness
The Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. It was created in 1812 by the German geologist and mineralogist Friedrich Mohs and is one of several definitions of hardness in...

) , 8.8 GPa
Tensile strength
Tensile strength
Ultimate tensile strength , often shortened to tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract...

: 48.3 MPa
Compressive strength
Compressive strength
Compressive strength is the capacity of a material or structure to withstand axially directed pushing forces. When the limit of compressive strength is reached, materials are crushed. Concrete can be made to have high compressive strength, e.g...

: >1.1 GPa
Bulk modulus
Bulk modulus
The bulk modulus of a substance measures the substance's resistance to uniform compression. It is defined as the pressure increase needed to decrease the volume by a factor of 1/e...

: ~37 GPa
Rigidity modulus: 31 GPa
Young's modulus
Young's modulus
Young's modulus is a measure of the stiffness of an elastic material and is a quantity used to characterize materials. It is defined as the ratio of the uniaxial stress over the uniaxial strain in the range of stress in which Hooke's Law holds. In solid mechanics, the slope of the stress-strain...

: 71.7 GPa
Poisson's ratio
Poisson's ratio
Poisson's ratio , named after Siméon Poisson, is the ratio, when a sample object is stretched, of the contraction or transverse strain , to the extension or axial strain ....

: 0.17
Lame elastic constants: λ=15.872 GPa, μ=31.261 GPa
Coefficient of thermal expansion: 5.5×10⁻⁷/°C (average from 20 °C to 320 °C)
Thermal conductivity
Thermal conductivity
In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....

: 1.3 W/(m·K)
Specific heat capacity: 45.3 J/(mol·K)
Softening point
Softening point
The softening point is the temperature at which a material softens beyond some arbitrary softness. It can be determined, for example, by the Vicat method , Heat Deflection Test or a ring and ball method ....

: c. 1665 °C
Annealing point
Annealing (glass)
Annealing is a process of slowly cooling glass to relieve internal stresses after it was formed. The process may be carried out in a temperature-controlled kiln known as a Lehr. Glass which has not been annealed is liable to crack or shatter when subjected to a relatively small temperature change...

: c. 1140 °C
Strain point: 1070 °C
Electrical resistivity: >10¹⁸ Ω·m
Dielectric constant
Dielectric constant
The relative permittivity of a material under given conditions reflects the extent to which it concentrates electrostatic lines of flux. In technical terms, it is the ratio of the amount of electrical energy stored in a material by an applied voltage, relative to that stored in a vacuum...

: 3.75 at 20 °C 1 MHz
Dielectric loss factor: less than 0.0004 at 20 °C 1 MHz
Index of refraction
Refractive index
In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....

: 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)
Strain-optic coefficients: p₁₁=0.113, p₁₂=0.252.
Hamaker constant
Hamaker Constant
The Hamaker constant A can be defined for a Van der Waals body-body interaction:A=\pi^2\times C \times \rho_1 \times \rho_2where \rho_1 and \rho_2 are the number of atoms per unit volume in two interacting bodies and C is the coefficient in the particle-particle pair interaction.The Hamaker...

: A=6.5 zJ.
Dielectric strength
Dielectric strength
In physics, the term dielectric strength has the following meanings:*Of an insulating material, the maximum electric field strength that it can withstand intrinsically without breaking down, i.e., without experiencing failure of its insulating properties....

: 250–400 kV/cm at 20 °C

External Links

"Frozen Eye to Bring New Worlds into View" Popular Mechanics, June 1931 General Electrics, West Lynn Massachusetts Labs work on large fuzed quartz blocks

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Chemistry

Applications

Physical properties

Typical properties of clear fused silica

See also

External Links