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Duct tape

Duct tape (historically and still occasionally referred to as duck tape) is cloth- or scrim-backed pressure-sensitive tape, often coated with polyethylene. There are a variety of constructions using different backings and adhesives, and the term 'duct tape' has been genericized to refer to different cloth tapes with differing purposes. A variation is heat-resistant foil tape useful for sealing heating and cooling ducts, produced because the adhesive on standard duct tape fails and the synthetic fabric reinforcement mesh deteriorates when used on heating ducts.

Duct tape is generally silvery gray in color, but also available in other colors and printed designs, from whimsical yellow ducks, college logos to practical camouflage patterns. It is often confused with gaffer tape (which is designed to be non-reflective and cleanly removed, unlike duct tape).

During World War II, Revolite (then a division of Johnson & Johnson) developed an adhesive tape made from a rubber-based adhesive applied to a durable duck cloth backing. This tape resisted water and was used to seal some ammunition cases during that period.

"Duck tape" is recorded in the Oxford English Dictionary as having been in use since 1899 and "duct tape" (described as "perhaps an alteration of earlier duck tape") since 1965.

History

The first material called "duck tape" was long strips of plain non-adhesive cotton duck cloth used in making shoes stronger, for decoration on clothing, and for wrapping steel cables or electrical conductors to protect them from corrosion or wear. For instance, in 1902, steel cables supporting the Manhattan Bridge were first covered in linseed oil then wrapped in duck tape before being laid in place. In the 1910s, certain boots and shoes used canvas duck fabric for the upper or for the insole, and duck tape was sometimes sewn in for reinforcement. In 1936, the US-based Insulated Power Cables Engineers Association specified a wrapping of duck tape as one of many methods used to protect rubber-insulated power cables. In 1942, Gimbel's department store offered venetian blinds that were held together with vertical strips of duck tape.

Glue backed or impregnated adhesive tapes of various sorts were in use by the 1910s, including rolls of cloth tape with adhesive coating one side. White adhesive tape made of cloth soaked in rubber and zinc oxide was used in hospitals to bind wounds, but other tapes such as friction tape or electrical tape could be substituted in an emergency. In 1930, the magazine Popular Mechanics described how to make adhesive tape at home using plain cloth tape soaked in a heated liquid mixture of rosin and rubber from inner tubes.

In 1923, tape pioneer Richard Gurley Drew at 3M invented masking tape, a paper-based tape with a mildly sticky adhesive intended to be temporarily used and removed rather than left in place permanently. In 1925 this became the Scotch brand masking tape. In 1930, Drew developed a transparent cellophane-based tape, dubbed Scotch Tape. This tape was widely used beginning in the Great Depression to repair household items. Neither of these inventions was based on cloth tape.

The ultimate wide-scale adoption of duck tape, today generally referred to as duct tape, came from Vesta Stoudt. Stoudt was worried that problems with ammunition box seals could cost soldiers precious time in battle, so she wrote to President Franklin D. Roosevelt in 1943 with the idea to seal the boxes with a fabric tape which she had tested. The letter was forwarded to the War Production Board, which put Johnson & Johnson on the job. The Revolite division of Johnson & Johnson had made medical adhesive tapes from duck cloth from 1927 and a team headed by Revolite's Johnny Denoye and Johnson & Johnson's Bill Gross developed the new adhesive tape, designed to be ripped by hand, not cut with scissors.

Their new unnamed product was made of thin cotton duck coated in waterproof polyethylene (plastic) with a layer of rubber-based gray adhesive (branded as "Polycoat") bonded to one side. It was easy to apply and remove, and was soon adapted to repair military equipment quickly, including vehicles and weapons. This tape, colored in army-standard matte olive drab, was widely used by the soldiers. After the war, the duck tape product was sold in hardware stores for household repairs. The Melvin A. Anderson Company of Cleveland, Ohio, acquired the rights to the tape in 1950. It was commonly used in construction to wrap air ducts. Following this application, the name "duct tape" came into use in the 1950s, along with tape products that were colored silvery gray like tin ductwork. Specialized heat- and cold-resistant tapes were developed for heating and air-conditioning ducts. By 1960 a St. Louis, Missouri, HVAC company, Albert Arno, Inc., trademarked the name "Ductape" for their "flame-resistant" duct tape, capable of holding together at 350 –.

In 1971, Jack Kahl bought the Anderson firm and renamed it Manco. In 1975, Kahl rebranded the duct tape made by his company. Because the previously used generic term "duck tape" had fallen out of use, he was able to trademark the brand "Duck Tape" and market his product complete with a yellow cartoon duck logo. Manco chose the term "Duck", the tape's original name, as "a play on the fact that people often refer to duct tape as 'duck tape, and as a marketing differentiation to stand out against other sellers of duct tape. In 1979, the Duck Tape marketing plan involved sending out greeting cards with the duck branding, four times a year, to 32,000 hardware managers. This mass of communication combined with colorful, convenient packaging helped Duck Tape become popular. From a near-zero customer base Manco eventually controlled 40% of the duct tape market in the US.  Acquired by Henkel in 1998, Duck Tape was sold to Shurtape Technologies in 2009.  Shurtape went on to introduce a premium version called "T-Rex Tape." "Ultimate Duck", which had been Henkel's top-of-the-line variety, is still sold in the United Kingdom. Ultimate Duck, T-Rex Tape, and the competing Gorilla Tape all advertise "three-layer technology".

After profiting from Scotch Tape in the 1930s, 3M had produced military materiel during World War II, and by 1946 had developed the first practical vinyl electrical tape. By 1977, the company was selling a heat-resistant duct tape for heating ducts. In the late 1990s, 3M's tape division had an annual turnover of $300 million, and was the US industry leader. In 2004, 3M released a semi-transparent duct tape, with a clear polyethylene film and white fiberglass mesh.

Manufacture
Modern duct tape is made variously from cotton, polyester, nylon, rayon or fiberglass mesh fabric to provide strength. The fabric, a very thin gauze called "scrim", is laminated to a backing of low-density polyethylene (LDPE). The color of the LDPE is provided by various pigments; the usual gray color comes from powdered aluminum mixed into the LDPE. Two tape widths are common: 1.9 in and 2 in. Other widths are also offered. The largest commercial rolls of duct tape were made in 2005 for Henkel, with 3.78 in width, a roll diameter of 64 in and weighing 650 lb.

Common uses
Duct tape is commonly used in situations that require a strong, flexible, and very sticky tape. Some have a long-lasting adhesive and resistance to weathering.

A specialized version, gaffer tape, which does not leave a sticky residue when removed, is preferred by gaffers in the theatre, motion picture and television industries.

Ductwork
The product now commonly called duct tape has largely been displaced in HVAC uses with specialized foil tapes designed for sealing heating and ventilation ducts (sometimes referred to erroneously as "duct tapes").

Common duct tape carries no safety certifications such as UL or Proposition 65, which means the tape may burn violently, producing toxic smoke; it may cause ingestion and contact toxicity; it can have irregular mechanical strength; and its adhesive may have low life expectancy. Its use in ducts has been prohibited by the state of California and by building codes in many other places.

Research was conducted in 1998 on standard duct tape at Lawrence Berkeley National Laboratory, Environmental Energy Technologies Division, which concluded that under challenging but realistic conditions duct tape becomes brittle, fails, and may even fall off completely.

Spaceflight
"Interviewer: And duct tape works in the vacuum of space as well as it does here? Walker: Oh, yes. Yes, it does. It sticks."

- Charles D. Walker, describing duct tape's use on STS-51-D

According to NASA engineer Jerry Woodfill duct tape had been stowed on board every mission since early in the Gemini program.

NASA engineers and astronauts have used duct tape in their work, including in some emergency situations. One such usage occurred in 1970 when Woodfill was working in Mission Control, when the square carbon dioxide filters from Apollo 13's failed command module had to be modified to fit round receptacles in the lunar module, which was being used as a lifeboat after an explosion en route to the Moon. A workaround used duct tape and other items on board Apollo 13, with the ground crew relaying instructions to the flight crew. The lunar module's CO2 scrubbers started working again, saving the lives of the three astronauts on board.

Ed Smylie, who designed the scrubber modification in just two days, said later that he knew the problem was solvable when it was confirmed that duct tape was on the spacecraft: "I felt like we were home free," he said in 2005. "One thing a Southern boy will never say is, 'I don't think duct tape will fix it.'"

Duct tape, referred to as "...good old-fashioned American gray tape..." was used by the Apollo 17 astronauts on the Moon to improvise a repair to a damaged fender on the lunar rover, preventing possible damage from the spray of lunar dust as they drove.

Military
In the US submarine fleet, an adhesive cloth tape is called "EB Green," as the duct tape used by Electric Boat was green. It is also called "duck tape", "riggers' tape", "hurricane tape", or "100-mph tape"; a name that comes from the use of a specific variety of duct tape that was supposed to withstand up to 100 mph winds. The tape is so named because it was used during the Vietnam War to repair or balance helicopter rotor blades.

Alternative uses

Duct tape's widespread popularity and multitude of uses has earned it a strong place in popular culture, and has inspired a vast number of creative and imaginative applications.

Duct tape occlusion therapy (DTOT) is a method intended to treat warts by covering them with duct tape for an extended period. The evidence for its effectiveness is poor; thus it is not recommended as routine treatment. However, other studies suggest the duct tape treatment is more effective than existing medical options. Duct tape is often used in shoe repair due to its resiliency.

Duct tape has been used to temporarily fix Apple's iPhone 4 dropped call issue, as an alternative to Apple's own rubber case.

In popular culture
The Duct Tape Guys (Jim Berg and Tim Nyberg) have written seven books about duct tape,. Their books have sold over 1.5 million copies and feature real and unusual uses of duct tape. In 1994 they coined the phrase "it ain't broke, it just lacks duct tape".

The sitcom The Red Green Show title character often used duct tape (which he dubbed "the handyman's secret weapon") as both a shortcut to proper fastening as well as for unconventional uses. The series sometimes showcased fan duct tape creations. The series had a feature film based on it entitled Duct Tape Forever and several VHS/DVD compilations of the show's use of the tape have been released. Since 2000, series star Steve Smith (as "Red Green") has been the "Ambassador of Scotch Duct Tape" for 3M.

The Discovery Channel series MythBusters featured duct tape in a number of myths that involve non-traditional uses. Confirmed myths include suspending a car for a period of time, building a functional cannon, a two-person sailboat, a two-person canoe (with duct tape paddles), a two-person raft, Roman sandals, a chess set, a leak proof water canister, rope, a hammock that can support the weight of an adult male, holding a car in place, a bridge that spanned the width of a dry dock, and a full-scale functional trebuchet with duct tape as the only binder. In the episode "Duct Tape Plane", the MythBusters repaired (and eventually replaced) the skin of a lightweight airplane with duct tape and flew it a few meters above a runway.

Garrison Keillor's radio show A Prairie Home Companion included comedic fictional commercials sponsored by the "American Duct Tape Council".

Duct tape alert
The term duct tape alert refers to the recommendations made by the U.S. Department of Homeland Security on February 10, 2003, that Americans should prepare for a biological, chemical, or radiological terrorist attack by assembling a "disaster supply kit", including duct tape and plastic (presumably to attempt to seal one's home against nuclear, chemical, and biological contaminants), among other items.

The recommendations followed an increase in the Department's official threat level to "orange", or "high risk", citing "recent intelligence reports".

According to press reports, the recommendations caused a surge in demand for duct tape.

The media sensation surrounding duct tape was fodder for comedians and satirists. Some referred to it as "duct and cover", a reference to duck and cover.

Specifications

 * ASTM International ASTM D5486 Standard Specification for Pressure-Sensitive Tape for Packaging, Box Closure, and Sealing, Type IV woven cloth backing
 * ASTM D580 Standard Specification for Greige Woven Glass Tapes and Webbings
 * ASTM D4514-12 Standard Specification for Friction Tape
 * ASTM D2754-10 Standard Specification for High-Temperature Glass Cloth Pressure-Sensitive Electrical Insulating Tape
 * MODUK DEF STAN 81-25, EN-Tape Pressure-Sensitive Adhesive (Water Resistant Fabric)
 * McDonnell-Douglas DMS1968E
 * Lockheed LCP-86-1226-A
 * Boeing D 6-8099
 * Ford specification ESB-M3G71-B
 * etc.

Books

 * "Pressure-Sensitive Adhesives and Applications", Istvan Benedek, 2004, ISBN 0-8247-5059-4
 * "Pressure Sensitive Adhesive Tapes", J. Johnston, PSTC, 2003, ISBN 0-9728001-0-7
 * "Pressure Sensitive Formulation", I. Benedek, VSP, 2000, ISBN 90-6764-330-0

title: Duct tape


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Radiation pressure

Radiation pressure (also known as light pressure) is mechanical pressure exerted upon a surface due to the exchange of momentum between the object and the electromagnetic field. This includes the momentum of light or electromagnetic radiation of any wavelength that is absorbed, reflected, or otherwise emitted (e.g. black-body radiation) by matter on any scale (from macroscopic objects to dust particles to gas molecules). The associated force is called the radiation pressure force, or sometimes just the force of light.

The forces generated by radiation pressure are generally too small to be noticed under everyday circumstances; however, they are important in some physical processes and technologies. This particularly includes objects in outer space, where it is usually the main force acting on objects besides gravity, and where the net effect of a tiny force may have a large cumulative effect over long periods of time. For example, had the effects of the Sun's radiation pressure on the spacecraft of the Viking program been ignored, the spacecraft would have missed Mars orbit by about 15000 km. Radiation pressure from starlight is crucial in a number of astrophysical processes as well. The significance of radiation pressure increases rapidly at extremely high temperatures and can sometimes dwarf the usual gas pressure, for instance, in stellar interiors and thermonuclear weapons. Furthermore, large lasers operating in space have been suggested as a means of propelling sail craft in beam-powered propulsion.

Radiation pressure forces are the bedrock of laser technology and the branches of science that rely heavily on lasers and other optical technologies. That includes, but is not limited to, biomicroscopy (where light is used to irradiate and observe microbes, cells, and molecules), quantum optics, and optomechanics (where light is used to probe and control objects like atoms, qubits and macroscopic quantum objects). Direct applications of the radiation pressure force in these fields are, for example, laser cooling (the subject of the 1997 Nobel Prize in Physics), quantum control of macroscopic objects and atoms (2012 Nobel Prize in Physics), interferometry (2017 Nobel Prize in Physics) and optical tweezers (2018 Nobel Prize in Physics).

Radiation pressure can equally well be accounted for by considering the momentum of a classical electromagnetic field or in terms of the momenta of photons, particles of light. The interaction of electromagnetic waves or photons with matter may involve an exchange of momentum. Due to the law of conservation of momentum, any change in the total momentum of the waves or photons must involve an equal and opposite change in the momentum of the matter it interacted with (Newton's third law of motion), as is illustrated in the accompanying figure for the case of light being perfectly reflected by a surface. This transfer of momentum is the general explanation for what we term radiation pressure.

Discovery
Johannes Kepler put forward the concept of radiation pressure in 1619 to explain the observation that a tail of a comet always points away from the Sun.

The assertion that light, as electromagnetic radiation, has the property of momentum and thus exerts a pressure upon any surface that is exposed to it was published by James Clerk Maxwell in 1862, and proven experimentally by Russian physicist Pyotr Lebedev in 1900 and by Ernest Fox Nichols and Gordon Ferrie Hull in 1901. The pressure is very small, but can be detected by allowing the radiation to fall upon a delicately poised vane of reflective metal in a Nichols radiometer (this should not be confused with the Crookes radiometer, whose characteristic motion is not caused by radiation pressure but by air flow caused by temperature differentials.)

Theory
Radiation pressure can be viewed as a consequence of the conservation of momentum given the momentum attributed to electromagnetic radiation. That momentum can be equally well calculated on the basis of electromagnetic theory or from the combined momenta of a stream of photons, giving identical results as is shown below.

Radiation pressure from momentum of an electromagnetic wave
According to Maxwell's theory of electromagnetism, an electromagnetic wave carries momentum. Momentum will be transferred to any surface it strikes that absorbs or reflects the radiation.

Consider the momentum transferred to a perfectly absorbing (black) surface. The energy flux (irradiance) of a plane wave is calculated using the Poynting vector $\mathbf{S} = \mathbf{E} \times \mathbf{H}$, which is the cross product of the electric field vector E and the magnetic field's auxiliary field vector (or magnetizing field) H. The magnitude, denoted by S, divided by the speed of light is the density of the linear momentum per unit area (pressure) of the electromagnetic field. So, dimensionally, the Poynting vector is S = $power⁄area$ = $rate of doing work⁄area$ = $ΔF⁄Δt Δx⁄area$, which is the speed of light, c = Δx / Δt, times pressure, ΔF / area. That pressure is experienced as radiation pressure on the surface: $$ P_\text{incident} = \frac{\langle S\rangle}{c} = \frac{I_f}{c}$$ where $$P$$ is pressure (usually in pascals), $$I_f$$ is the incident irradiance (usually in W/m2) and $$c$$ is the speed of light in vacuum. Here, $1⁄c$ ≈ $3.34 N/GW$.

If the surface is planar at an angle α to the incident wave, the intensity across the surface will be geometrically reduced by the cosine of that angle and the component of the radiation force against the surface will also be reduced by the cosine of α, resulting in a pressure: $$ P_\text{incident} = \frac{I_f}{c} \cos^2 \alpha $$

The momentum from the incident wave is in the same direction of that wave. But only the component of that momentum normal to the surface contributes to the pressure on the surface, as given above. The component of that force tangent to the surface is not called pressure.

Radiation pressure from reflection
The above treatment for an incident wave accounts for the radiation pressure experienced by a black (totally absorbing) body. If the wave is specularly reflected, then the recoil due to the reflected wave will further contribute to the radiation pressure. In the case of a perfect reflector, this pressure will be identical to the pressure caused by the incident wave:

$$ P_\text{emitted} = \frac{I_f}{c}$$

thus doubling the net radiation pressure on the surface:

$$ P_\text{net} =  P_\text{incident} +  P_\text{emitted} = 2 \frac{I_f}{c}$$

For a partially reflective surface, the second term must be multiplied by the reflectivity (also known as reflection coefficient of intensity), so that the increase is less than double. For a diffusely reflective surface, the details of the reflection and geometry must be taken into account, again resulting in an increased net radiation pressure of less than double.

Radiation pressure by emission
Just as a wave reflected from a body contributes to the net radiation pressure experienced, a body that emits radiation of its own (rather than reflected) obtains a radiation pressure again given by the irradiance of that emission in the direction normal to the surface Ie: $$ P_\text{emitted} = \frac{I_\text{e}}{c}$$

The emission can be from black-body radiation or any other radiative mechanism. Since all materials emit black-body radiation (unless they are totally reflective or at absolute zero), this source for radiation pressure is ubiquitous but usually tiny. However, because black-body radiation increases rapidly with temperature (as the fourth power of temperature, given by the Stefan–Boltzmann law), radiation pressure due to the temperature of a very hot object (or due to incoming black-body radiation from similarly hot surroundings) can become significant. This is important in stellar interiors.

Radiation pressure in terms of photons
Electromagnetic radiation can be viewed in terms of particles rather than waves; these particles are known as photons. Photons do not have a rest-mass; however, photons are never at rest (they move at the speed of light) and acquire a momentum nonetheless which is given by: $$ p = \dfrac{h}{\lambda} = \frac{E_p}{c}, $$ where $p$ is momentum, $h$ is the Planck constant, $λ$ is wavelength, and $c$ is speed of light in vacuum. And $E_{p}$ is the energy of a single photon given by: $$ E_p = h \nu = \frac{h c}{\lambda} $$

The radiation pressure again can be seen as the transfer of each photon's momentum to the opaque surface, plus the momentum due to a (possible) recoil photon for a (partially) reflecting surface. Since an incident wave of irradiance $I_{f}$ over an area $A$ has a power of $I_{f}A$, this implies a flux of $I_{f}/E_{p}$ photons per second per unit area striking the surface. Combining this with the above expression for the momentum of a single photon, results in the same relationships between irradiance and radiation pressure described above using classical electromagnetics. And again, reflected or otherwise emitted photons will contribute to the net radiation pressure identically.

Compression in a uniform radiation field
In general, the pressure of electromagnetic waves can be obtained from the vanishing of the trace of the electromagnetic stress tensor: since this trace equals 3P − u, we get $$P = \frac{u}{3},$$ where $u$ is the radiation energy per unit volume.

This can also be shown in the specific case of the pressure exerted on surfaces of a body in thermal equilibrium with its surroundings, at a temperature $T$: the body will be surrounded by a uniform radiation field described by the Planck black-body radiation law and will experience a compressive pressure due to that impinging radiation, its reflection, and its own black-body emission. From that it can be shown that the resulting pressure is equal to one third of the total radiant energy per unit volume in the surrounding space.

By using Stefan–Boltzmann law, this can be expressed as $$P_\text{compress} = \frac{u}{3} = \frac{4\sigma}{3c} T^4,$$ where $$\sigma$$ is the Stefan–Boltzmann constant.

Solar radiation pressure
Solar radiation pressure is due to the Sun's radiation at closer distances, thus especially within the Solar System. (The radiation pressure of sunlight on Earth is very small: it is equivalent to that exerted by the weight of about a milligram on an area of 1 square metre, or 10 μN/m2.) While it acts on all objects, its net effect is generally greater on smaller bodies, since they have a larger ratio of surface area to mass. All spacecraft experience such a pressure, except when they are behind the shadow of a larger orbiting body.

Solar radiation pressure on objects near the Earth may be calculated using the Sun's irradiance at 1 AU, known as the solar constant, or GSC, whose value is set at 1361 W/m2 as of 2011.

All stars have a spectral energy distribution that depends on their surface temperature. The distribution is approximately that of black-body radiation. This distribution must be taken into account when calculating the radiation pressure or identifying reflector materials for optimizing a solar sail, for instance.

Momentary or hours long solar pressures can indeed escalate due to release of solar flares and coronal mass ejections, but effects remain essentially immeasureable in relation to Earth's orbit. However these pressures persist over eons, such that cumulatively having produced a measureable movement on the Earth-Moon system's orbit.

Pressures of absorption and reflection
Solar radiation pressure at the Earth's distance from the Sun, may be calculated by dividing the solar constant GSC (above) by the speed of light c. For an absorbing sheet facing the Sun, this is simply: $$P = \frac{G_\text{SC}}{c} \approx 4.5 \cdot 10^{-6}~\text{Pa} = 4.5~\mu\text{Pa}.$$

This result is in pascals, equivalent to N/m2 (newtons per square meter). For a sheet at an angle α to the Sun, the effective area A of a sheet is reduced by a geometrical factor resulting in a force in the direction of the sunlight of: $$F = \frac{G_\text{SC}}{c} (A \cos \alpha).$$

To find the component of this force normal to the surface, another cosine factor must be applied resulting in a pressure P on the surface of: $$P = \frac{F \cos \alpha }{A} = \frac{G_\text{SC}}{c} \cos^2 \alpha.$$

Note, however, that in order to account for the net effect of solar radiation on a spacecraft for instance, one would need to consider the total force (in the direction away from the Sun) given by the preceding equation, rather than just the component normal to the surface that we identify as "pressure".

The solar constant is defined for the Sun's radiation at the distance to the Earth, also known as one astronomical unit (au). Consequently, at a distance of R astronomical units (R thus being dimensionless), applying the inverse-square law, we would find: $$P = \frac{G_\text{SC}}{c R^2} \cos^2 \alpha.$$

Finally, considering not an absorbing but a perfectly reflecting surface, the pressure is doubled due to the reflected wave, resulting in: $$P = 2\frac{G_\text{SC}}{c R^2} \cos^2 \alpha.$$

Note that unlike the case of an absorbing material, the resulting force on a reflecting body is given exactly by this pressure acting normal to the surface, with the tangential forces from the incident and reflecting waves canceling each other. In practice, materials are neither totally reflecting nor totally absorbing, so the resulting force will be a weighted average of the forces calculated using these formulas.

Radiation pressure perturbations
Solar radiation pressure is a source of orbital perturbations. It significantly affects the orbits and trajectories of small bodies including all spacecraft.

Solar radiation pressure affects bodies throughout much of the Solar System. Small bodies are more affected than large ones because of their lower mass relative to their surface area. Spacecraft are affected along with natural bodies (comets, asteroids, dust grains, gas molecules).

The radiation pressure results in forces and torques on the bodies that can change their translational and rotational motions. Translational changes affect the orbits of the bodies. Rotational rates may increase or decrease. Loosely aggregated bodies may break apart under high rotation rates. Dust grains can either leave the Solar System or spiral into the Sun.

A whole body is typically composed of numerous surfaces that have different orientations on the body. The facets may be flat or curved. They will have different areas. They may have optical properties differing from other aspects.

At any particular time, some facets are exposed to the Sun, and some are in shadow. Each surface exposed to the Sun is reflecting, absorbing, and emitting radiation. Facets in shadow are emitting radiation. The summation of pressures across all of the facets defines the net force and torque on the body. These can be calculated using the equations in the preceding sections.

The Yarkovsky effect affects the translation of a small body. It results from a face leaving solar exposure being at a higher temperature than a face approaching solar exposure. The radiation emitted from the warmer face is more intense than that of the opposite face, resulting in a net force on the body that affects its motion.

The YORP effect is a collection of effects expanding upon the earlier concept of the Yarkovsky effect, but of a similar nature. It affects the spin properties of bodies.

The Poynting–Robertson effect applies to grain-size particles. From the perspective of a grain of dust circling the Sun, the Sun's radiation appears to be coming from a slightly forward direction (aberration of light). Therefore, the absorption of this radiation leads to a force with a component against the direction of movement. (The angle of aberration is tiny, since the radiation is moving at the speed of light, while the dust grain is moving many orders of magnitude slower than that.) The result is a gradual spiral of dust grains into the Sun. Over long periods of time, this effect cleans out much of the dust in the Solar System.

While rather small in comparison to other forces, the radiation pressure force is inexorable. Over long periods of time, the net effect of the force is substantial. Such feeble pressures can produce marked effects upon minute particles like gas ions and electrons, and are essential in the theory of electron emission from the Sun, of cometary material, and so on.

Because the ratio of surface area to volume (and thus mass) increases with decreasing particle size, dusty (micrometre-size) particles are susceptible to radiation pressure even in the outer Solar System. For example, the evolution of the outer rings of Saturn is significantly influenced by radiation pressure.

As a consequence of light pressure, Einstein in 1909 predicted the existence of "radiation friction", which would oppose the movement of matter. He wrote: "radiation will exert pressure on both sides of the plate. The forces of pressure exerted on the two sides are equal if the plate is at rest. However, if it is in motion, more radiation will be reflected on the surface that is ahead during the motion (front surface) than on the back surface. The backward acting force of pressure exerted on the front surface is thus larger than the force of pressure acting on the back. Hence, as the resultant of the two forces, there remains a force that counteracts the motion of the plate and that increases with the velocity of the plate. We will call this resultant 'radiation friction' in brief."

Solar sails
Solar sailing, an experimental method of spacecraft propulsion, uses radiation pressure from the Sun as a motive force. The idea of interplanetary travel by light was mentioned by Jules Verne in his 1865 novel From the Earth to the Moon.

A sail reflects about 90% of the incident radiation. The 10% that is absorbed is radiated away from both surfaces, with the proportion emitted from the unlit surface depending on the thermal conductivity of the sail. A sail has curvature, surface irregularities, and other minor factors that affect its performance.

The Japan Aerospace Exploration Agency (JAXA) has successfully unfurled a solar sail in space, which has already succeeded in propelling its payload with the IKAROS project.

Cosmic effects of radiation pressure
Radiation pressure has had a major effect on the development of the cosmos, from the birth of the universe to ongoing formation of stars and shaping of clouds of dust and gasses on a wide range of scales.

Early universe
The photon epoch is a phase when the energy of the universe was dominated by photons, between 10 seconds and 380,000 years after the Big Bang.

Galaxy formation and evolution
The process of galaxy formation and evolution began early in the history of the cosmos. Observations of the early universe strongly suggest that objects grew from bottom-up (i.e., smaller objects merging to form larger ones). As stars are thereby formed and become sources of electromagnetic radiation, radiation pressure from the stars becomes a factor in the dynamics of remaining circumstellar material.

Clouds of dust and gases
The gravitational compression of clouds of dust and gases is strongly influenced by radiation pressure, especially when the condensations lead to star births. The larger young stars forming within the compressed clouds emit intense levels of radiation that shift the clouds, causing either dispersion or condensations in nearby regions, which influences birth rates in those nearby regions.

Clusters of stars
Stars predominantly form in regions of large clouds of dust and gases, giving rise to star clusters. Radiation pressure from the member stars eventually disperses the clouds, which can have a profound effect on the evolution of the cluster.

Many open clusters are inherently unstable, with a small enough mass that the escape velocity of the system is lower than the average velocity of the constituent stars. These clusters will rapidly disperse within a few million years. In many cases, the stripping away of the gas from which the cluster formed by the radiation pressure of the hot young stars reduces the cluster mass enough to allow rapid dispersal.

Star formation
Star formation is the process by which dense regions within molecular clouds in interstellar space collapse to form stars. As a branch of astronomy, star formation includes the study of the interstellar medium and giant molecular clouds (GMC) as precursors to the star formation process, and the study of protostars and young stellar objects as its immediate products. Star formation theory, as well as accounting for the formation of a single star, must also account for the statistics of binary stars and the initial mass function.

Stellar planetary systems
Planetary systems are generally believed to form as part of the same process that results in star formation. A protoplanetary disk forms by gravitational collapse of a molecular cloud, called a solar nebula, and then evolves into a planetary system by collisions and gravitational capture. Radiation pressure can clear a region in the immediate vicinity of the star. As the formation process continues, radiation pressure continues to play a role in affecting the distribution of matter. In particular, dust and grains can spiral into the star or escape the stellar system under the action of radiation pressure.

Stellar interiors
In stellar interiors the temperatures are very high. Stellar models predict a temperature of 15 MK in the center of the Sun, and at the cores of supergiant stars the temperature may exceed 1 GK. As the radiation pressure scales as the fourth power of the temperature, it becomes important at these high temperatures. In the Sun, radiation pressure is still quite small when compared to the gas pressure. In the heaviest non-degenerate stars, radiation pressure is the dominant pressure component.

Comets
Solar radiation pressure strongly affects comet tails. Solar heating causes gases to be released from the comet nucleus, which also carry away dust grains. Radiation pressure and solar wind then drive the dust and gases away from the Sun's direction. The gases form a generally straight tail, while slower moving dust particles create a broader, curving tail.

Optical tweezers
Lasers can be used as a source of monochromatic light with wavelength $$\lambda$$. With a set of lenses, one can focus the laser beam to a point that is $$\lambda$$ in diameter (or $$r = \lambda/2$$).

The radiation pressure of a P = 30 mW laser with λ = 1064 nm can therefore be computed as follows.

Area: $$A = \pi\left(\frac{\lambda}{2}\right)^2 \approx 10^{-12} \text{ m}^2,$$

force: $$F = \frac{P}{c} = \frac{30 \text{ mW}} {299792458 \text{ m/s}} \approx 10^{-10} \text{ N},$$

pressure: $$p = \frac{F}{A} \approx \frac{10^{-10} \text{ N}} {10^{-12} \text{ m}^2} = 100 \text{ Pa}.$$

This is used to trap or levitate particles in optical tweezers.

Light–matter interactions

The reflection of a laser pulse from the surface of an elastic solid can give rise to various types of elastic waves that propagate inside the solid or liquid. In other words, the light can excite and/or amplify motion of, and in, materials. This is the subject of study in the field of optomechanics. The weakest waves are generally those that are generated by the radiation pressure acting during the reflection of the light. Such light-pressure-induced elastic waves have for example observed inside an ultrahigh-reflectivity dielectric mirror. These waves are the most basic fingerprint of a light-solid matter interaction on the macroscopic scale. In the field of cavity optomechanics, light is trapped and resonantly enhanced in optical cavities, for example between mirrors. This serves the purpose of gravely enhancing the power of the light, and the radiation pressure it can exert on objects and materials. Optical control (that is, manipulation of the motion) of a plethora of objects has been realized: from kilometers long beams (such as in the LIGO interferometer) to clouds of atoms, and from micro-engineered trampolines to superfluids.

Opposite to exciting or amplifying motion, light can also damp the motion of objects. Laser cooling is a method of cooling materials very close to absolute zero by converting some of material's motional energy into light. Kinetic energy and thermal energy of the material are synonyms here, because they represent the energy associated with Brownian motion of the material. Atoms traveling towards a laser light source perceive a doppler effect tuned to the absorption frequency of the target element. The radiation pressure on the atom slows movement in a particular direction until the Doppler effect moves out of the frequency range of the element, causing an overall cooling effect.

An other active research area of laser–matter interaction is the radiation pressure acceleration of ions or protons from thin–foil targets. High ion energy beams can be generated for medical applications (for example in ion beam therapy ) by the radiation pressure of short laser pulses on ultra-thin foils.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Radiation pressure


text:
Silicon dioxide

Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula SiO2, commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is abundant as it comprises several minerals and synthetic products. All forms are white or colorless, although impure samples can be colored.

Silicon dioxide is a common fundamental constituent of glass.

Structure
In the majority of silicon dioxides, the silicon atom shows tetrahedral coordination, with four oxygen atoms surrounding a central Si atom (see 3-D Unit Cell). Thus, SiO2 forms 3-dimensional network solids in which each silicon atom is covalently bonded in a tetrahedral manner to 4 oxygen atoms. In contrast, CO2 is a linear molecule. The starkly different structures of the dioxides of carbon and silicon are a manifestation of the double bond rule.

Based on the crystal structural differences, silicon dioxide can be divided into two categories: crystalline and non-crystalline (amorphous). In crystalline form, this substance can be found naturally occurring as quartz, tridymite (high-temperature form), cristobalite (high-temperature form), stishovite (high-pressure form), and coesite (high-pressure form). On the other hand, amorphous silica can be found in nature as opal and diatomaceous earth. Quartz glass is a form of intermediate state between these structures.

All of these distinct crystalline forms always have the same local structure around Si and O. In α-quartz the Si–O bond length is 161 pm, whereas in α-tridymite it is in the range 154–171 pm. The Si–O–Si angle also varies between a low value of 140° in α-tridymite, up to 180° in β-tridymite. In α-quartz, the Si–O–Si angle is 144°.

Polymorphism
Alpha quartz is the most stable form of solid SiO2 at room temperature. The high-temperature minerals, cristobalite and tridymite, have both lower densities and indices of refraction than quartz. The transformation from α-quartz to beta-quartz takes place abruptly at 573 °C. Since the transformation is accompanied by a significant change in volume, it can easily induce fracturing of ceramics or rocks passing through this temperature limit. The high-pressure minerals, seifertite, stishovite, and coesite, though, have higher densities and indices of refraction than quartz. Stishovite has a rutile-like structure where silicon is 6-coordinate. The density of stishovite is 4.287 g/cm3, which compares to α-quartz, the densest of the low-pressure forms, which has a density of 2.648 g/cm3. The difference in density can be ascribed to the increase in coordination as the six shortest Si–O bond lengths in stishovite (four Si–O bond lengths of 176 pm and two others of 181 pm) are greater than the Si–O bond length (161 pm) in α-quartz. The change in the coordination increases the ionicity of the Si–O bond.

Faujasite silica, another polymorph, is obtained by the dealumination of a low-sodium, ultra-stable Y zeolite with combined acid and thermal treatment. The resulting product contains over 99% silica, and has high crystallinity and specific surface area (over 800 m2/g). Faujasite-silica has very high thermal and acid stability. For example, it maintains a high degree of long-range molecular order or crystallinity even after boiling in concentrated hydrochloric acid.

Molten SiO2
Molten silica exhibits several peculiar physical characteristics that are similar to those observed in liquid water: negative temperature expansion, density maximum at temperatures ~5000 °C, and a heat capacity minimum. Its density decreases from 2.08 g/cm3 at 1950 °C to 2.03 g/cm3 at 2200 °C.

Molecular SiO2
The molecular SiO2 has a linear structure like. It has been produced by combining silicon monoxide (SiO) with oxygen in an argon matrix. The dimeric silicon dioxide, (SiO2)2 has been obtained by reacting O2 with matrix isolated dimeric silicon monoxide, (Si2O2). In dimeric silicon dioxide there are two oxygen atoms bridging between the silicon atoms with an Si–O–Si angle of 94° and bond length of 164.6 pm and the terminal Si–O bond length is 150.2 pm. The Si–O bond length is 148.3 pm, which compares with the length of 161 pm in α-quartz. The bond energy is estimated at 621.7 kJ/mol.

Geology
SiO2 is most commonly encountered in nature as quartz, which comprises more than 10% by mass of the Earth's crust. Quartz is the only polymorph of silica stable at the Earth's surface. Metastable occurrences of the high-pressure forms coesite and stishovite have been found around impact structures and associated with eclogites formed during ultra-high-pressure metamorphism. The high-temperature forms of tridymite and cristobalite are known from silica-rich volcanic rocks. In many parts of the world, silica is the major constituent of sand.

Biology
Even though it is poorly soluble, silica occurs in many plants such as rice. Plant materials with high silica phytolith content appear to be of importance to grazing animals, from chewing insects to ungulates. Silica accelerates tooth wear, and high levels of silica in plants frequently eaten by herbivores may have developed as a defense mechanism against predation.

Silica is also the primary component of rice husk ash, which is used, for example, in filtration and as supplementary cementitious material (SCM) in cement and concrete manufacturing.

Silicification in and by cells has been common in the biological world and it occurs in bacteria, protists, plants, and animals (invertebrates and vertebrates).

Prominent examples include:
 * Tests or frustules (i.e. shells) of diatoms, Radiolaria, and testate amoebae.
 * Silica phytoliths in the cells of many plants including Equisetaceae, many grasses, and a wide range of dicotyledons.
 * The spicules forming the skeleton of many sponges.

Structural use
About 95% of the commercial use of silicon dioxide (sand) occurs in the construction industry, e.g. for the production of concrete (Portland cement concrete).

Certain deposits of silica sand, with desirable particle size and shape and desirable clay and other mineral content, were important for sand casting of metallic products. The high melting point of silica enables it to be used in such applications such as iron casting; modern sand casting sometimes uses other minerals for other reasons.

Crystalline silica is used in hydraulic fracturing of formations which contain tight oil and shale gas.

Precursor to glass and silicon
Silica is the primary ingredient in the production of most glass. As other minerals are melted with silica, the principle of freezing point depression lowers the melting point of the mixture and increases fluidity. The glass transition temperature of pure SiO2 is about 1475 K. When molten silicon dioxide SiO2 is rapidly cooled, it does not crystallize, but solidifies as a glass. Because of this, most ceramic glazes have silica as the main ingredient.

The structural geometry of silicon and oxygen in glass is similar to that in quartz and most other crystalline forms of silicon and oxygen with silicon surrounded by regular tetrahedra of oxygen centres. The difference between the glass and crystalline forms arises from the connectivity of the tetrahedral units: Although there is no long-range periodicity in the glassy network ordering remains at length scales well beyond the SiO bond length. One example of this ordering is the preference to form rings of 6-tetrahedra.

The majority of optical fibers for telecommunication are also made from silica. It is a primary raw material for many ceramics such as earthenware, stoneware, and porcelain.

Silicon dioxide is used to produce elemental silicon. The process involves carbothermic reduction in an electric arc furnace:

Fumed silica
Fumed silica, also known as pyrogenic silica, is prepared by burning SiCl4 in an oxygen-rich hydrogen flame to produce a "smoke" of SiO2.

It can also be produced by vaporizing quartz sand in a 3000 °C electric arc. Both processes result in microscopic droplets of amorphous silica fused into branched, chainlike, three-dimensional secondary particles which then agglomerate into tertiary particles, a white powder with extremely low bulk density (0.03-0.15 g/cm3) and thus high surface area. The particles act as a thixotropic thickening agent, or as an anti-caking agent, and can be treated to make them hydrophilic or hydrophobic for either water or organic liquid applications

Silica fume is an ultrafine powder collected as a by-product of the silicon and ferrosilicon alloy production. It consists of amorphous (non-crystalline) spherical particles with an average particle diameter of 150 nm, without the branching of the pyrogenic product. The main use is as pozzolanic material for high performance concrete. Fumed silica nanoparticles can be successfully used as an anti-aging agent in asphalt binders.

Food, cosmetic, and pharmaceutical applications
Silica, either colloidal, precipitated, or pyrogenic fumed, is a common additive in food production. It is used primarily as a flow or anti-caking agent in powdered foods such as spices and non-dairy coffee creamer, or powders to be formed into pharmaceutical tablets. It can adsorb water in hygroscopic applications. Colloidal silica is used as a fining agent for wine, beer, and juice, with the E number reference E551.

In cosmetics, silica is useful for its light-diffusing properties and natural absorbency.

Diatomaceous earth, a mined product, has been used in food and cosmetics for centuries. It consists of the silica shells of microscopic diatoms; in a less processed form it was sold as "tooth powder". Manufactured or mined hydrated silica is used as the hard abrasive in toothpaste.

Semiconductors
Silicon dioxide is widely used in the semiconductor technology:

 * for the primary passivation (directly on the semiconductor surface),
 * as an original gate dielectric in MOS technology. Today when scaling (dimension of the gate length of the MOS transistor) has progressed below 10 nm, silicon dioxide has been replaced by other dielectric materials like hafnium oxide or similar with higher dielectric constant compared to silicon dioxide,
 * as a dielectric layer between metal (wiring) layers (sometimes up to 8–10) connecting elements and
 * as a second passivation layer (for protecting semiconductor elements and the metallization layers) typically today layered with some other dielectrics like silicon nitride.

Because silicon dioxide is a native oxide of silicon it is more widely used compared to other semiconductors like gallium arsenide or indium phosphide.

Silicon dioxide could be grown on a silicon semiconductor surface. Silicon oxide layers could protect silicon surfaces during diffusion processes, and could be used for diffusion masking.

Surface passivation is the process by which a semiconductor surface is rendered inert, and does not change semiconductor properties as a result of interaction with air or other materials in contact with the surface or edge of the crystal. The formation of a thermally grown silicon dioxide layer greatly reduces the concentration of electronic states at the silicon surface. SiO2 films preserve the electrical characteristics of p–n junctions and prevent these electrical characteristics from deteriorating by the gaseous ambient environment. Silicon oxide layers could be used to electrically stabilize silicon surfaces. The surface passivation process is an important method of semiconductor device fabrication that involves coating a silicon wafer with an insulating layer of silicon oxide so that electricity could reliably penetrate to the conducting silicon below. Growing a layer of silicon dioxide on top of a silicon wafer enables it to overcome the surface states that otherwise prevent electricity from reaching the semiconducting layer.

The process of silicon surface passivation by thermal oxidation (silicon dioxide) is critical to the semiconductor industry. It is commonly used to manufacture metal–oxide–semiconductor field-effect transistors (MOSFETs) and silicon integrated circuit chips (with the planar process).

Other
Hydrophobic silica is used as a defoamer component.

In its capacity as a refractory, it is useful in fiber form as a high-temperature thermal protection fabric.

Silica is used in the extraction of DNA and RNA due to its ability to bind to the nucleic acids under the presence of chaotropes.

Silica aerogel was used in the Stardust spacecraft to collect extraterrestrial particles.

Pure silica (silicon dioxide), when cooled as fused quartz into a glass with no true melting point, can be used as a glass fibre for fibreglass.

Production
Silicon dioxide is mostly obtained by mining, including sand mining and purification of quartz. Quartz is suitable for many purposes, while chemical processing is required to make a purer or otherwise more suitable (e.g. more reactive or fine-grained) product.

Precipitated silica
Precipitated silica or amorphous silica is produced by the acidification of solutions of sodium silicate. The gelatinous precipitate or silica gel, is first washed and then dehydrated to produce colorless microporous silica. The idealized equation involving a trisilicate and sulfuric acid is:

Approximately one billion kilograms/year (1999) of silica were produced in this manner, mainly for use for polymer composites – tires and shoe soles.

On microchips
Thin films of silica grow spontaneously on silicon wafers via thermal oxidation, producing a very shallow layer of about 1 nm or 10 Å of so-called native oxide. Higher temperatures and alternative environments are used to grow well-controlled layers of silicon dioxide on silicon, for example at temperatures between 600 and 1200 °C, using so-called dry oxidation with O2

or wet oxidation with H2O.

The native oxide layer is beneficial in microelectronics, where it acts as electric insulator with high chemical stability. It can protect the silicon, store charge, block current, and even act as a controlled pathway to limit current flow.

From organosilicon compounds
Many routes to silicon dioxide start with an organosilicon compound, e.g., HMDSO, TEOS. Synthesis of silica is illustrated below using tetraethyl orthosilicate (TEOS). Simply heating TEOS at 680–730 °C results in the oxide:

Similarly TEOS combusts around 400 °C:

TEOS undergoes hydrolysis via the so-called sol-gel process. The course of the reaction and nature of the product are affected by catalysts, but the idealized equation is:

Other methods
Being highly stable, silicon dioxide arises from many methods. Conceptually simple, but of little practical value, combustion of silane gives silicon dioxide. This reaction is analogous to the combustion of methane:

However the chemical vapor deposition of silicon dioxide onto crystal surface from silane had been used using nitrogen as a carrier gas at 200–500 °C.

Chemical reactions
Silicon dioxide is a relatively inert material (hence its widespread occurrence as a mineral). Silica is often used as inert containers for chemical reactions. At high temperatures, it is converted to silicon by reduction with carbon.

Fluorine reacts with silicon dioxide to form SiF4 and O2 whereas the other halogen gases (Cl2, Br2, I2) are unreactive.

Most forms of silicon dioxide are attacked ("etched") by hydrofluoric acid (HF) to produce hexafluorosilicic acid:
 * SiO2 + 6 HF -> H2SiF6 + 2 H2O

Stishovite does not react to HF to any significant degree. HF is used to remove or pattern silicon dioxide in the semiconductor industry.

Silicon dioxide acts as a Lux–Flood acid, being able to react with bases under certain conditions. As it does not contain any hydrogen, non-hydrated silica cannot directly act as a Brønsted–Lowry acid. While silicon dioxide is only poorly soluble in water at low or neutral pH (typically, 2 × 10−4 M for quartz up to 10−3 M for cryptocrystalline chalcedony), strong bases react with glass and easily dissolve it. Therefore, strong bases have to be stored in plastic bottles to avoid jamming the bottle cap, to preserve the integrity of the recipient, and to avoid undesirable contamination by silicate anions.

Silicon dioxide dissolves in hot concentrated alkali or fused hydroxide, as described in this idealized equation:

Silicon dioxide will neutralise basic metal oxides (e.g. sodium oxide, potassium oxide, lead(II) oxide, zinc oxide, or mixtures of oxides, forming silicates and glasses as the Si-O-Si bonds in silica are broken successively). As an example the reaction of sodium oxide and SiO2 can produce sodium orthosilicate, sodium silicate, and glasses, dependent on the proportions of reactants:

 * $$(0.25-0.8)$$.

Examples of such glasses have commercial significance, e.g. soda–lime glass, borosilicate glass, lead glass. In these glasses, silica is termed the network former or lattice former. The reaction is also used in blast furnaces to remove sand impurities in the ore by neutralisation with calcium oxide, forming calcium silicate slag.

Silicon dioxide reacts in heated reflux under dinitrogen with ethylene glycol and an alkali metal base to produce highly reactive, pentacoordinate silicates which provide access to a wide variety of new silicon compounds. The silicates are essentially insoluble in all polar solvent except methanol.

Silicon dioxide reacts with elemental silicon at high temperatures to produce SiO:

Water solubility
The solubility of silicon dioxide in water strongly depends on its crystalline form and is three to four times higher for amorphous silica than quartz; as a function of temperature, it peaks around 340 °C. This property is used to grow single crystals of quartz in a hydrothermal process where natural quartz is dissolved in superheated water in a pressure vessel that is cooler at the top. Crystals of 0.5–1 kg can be grown for 1–2 months. These crystals are a source of very pure quartz for use in electronic applications. Above the critical temperature of water 647.096 K and a pressure of 22.064 MPa or higher, water is a supercritical fluid and solubility is once again higher than at lower temperatures.

Health effects
Silica ingested orally is essentially nontoxic, with an of 5000 mg/kg (5 g/kg). A 2008 study following subjects for 15 years found that higher levels of silica in water appeared to decrease the risk of dementia. An increase of 10 mg/day of silica in drinking water was associated with a decreased risk of dementia of 11%.

Inhaling finely divided crystalline silica dust can lead to silicosis, bronchitis, or lung cancer, as the dust becomes lodged in the lungs and continuously irritates the tissue, reducing lung capacities. When fine silica particles are inhaled in large enough quantities (such as through occupational exposure), it increases the risk of systemic autoimmune diseases such as lupus and rheumatoid arthritis compared to expected rates in the general population.

Occupational hazard
Silica is an occupational hazard for people who do sandblasting or work with products that contain powdered crystalline silica. Amorphous silica, such as fumed silica, may cause irreversible lung damage in some cases but is not associated with the development of silicosis. Children, asthmatics of any age, those with allergies, and the elderly (all of whom have reduced lung capacity) can be affected in less time.

Crystalline silica is an occupational hazard for those working with stone countertops, because the process of cutting and installing the countertops creates large amounts of airborne silica. Crystalline silica used in hydraulic fracturing presents a health hazard to workers.

Pathophysiology
In the body, crystalline silica particles do not dissolve over clinically relevant periods. Silica crystals inside the lungs can activate the NLRP3 inflammasome inside macrophages and dendritic cells and thereby result in production of interleukin, a highly pro-inflammatory cytokine in the immune system.

Regulation
Regulations restricting silica exposure 'with respect to the silicosis hazard' specify that they are concerned only with silica, which is both crystalline and dust-forming.

In 2013, the U.S. Occupational Safety and Health Administration reduced the exposure limit to 50 μg/m3 of air. Prior to 2013, it had allowed 100 μg/m3 and in construction workers even 250 μg/m3. In 2013, OSHA also required "green completion" of fracked wells to reduce exposure to crystalline silica besides restricting the limit of exposure.

Crystalline forms
SiO2, more so than almost any material, exists in many crystalline forms. These forms are called polymorphs.

Safety
Inhaling finely divided crystalline silica can lead to severe inflammation of the lung tissue, silicosis, bronchitis, lung cancer, and systemic autoimmune diseases, such as lupus and rheumatoid arthritis. Inhalation of amorphous silicon dioxide, in high doses, leads to non-permanent short-term inflammation, where all effects heal.

Other names
This extended list enumerates synonyms for silicon dioxide; all of these values are from a single source; values in the source were presented capitalized.

• CAS 112945-52-5

• Acitcel

• Aerosil

• Amorphous silica dust

• Aquafil

• CAB-O-GRIP II

• CAB-O-SIL

• CAB-O-SPERSE

• Catalogue

• Colloidal silica

• Colloidal silicon dioxide

• Dicalite

• DRI-DIE Insecticide 67

• FLO-GARD

• Fossil flour

• Fumed silica

• Fumed silicon dioxide

• HI-SEL

• LO-VEL

• Ludox

• Nalcoag

• Nyacol

• Santocel

• Silica

• Silica aerogel

• Silica, amorphous

• Silicic anhydride

• Silikill

• Synthetic amorphous silica

• Vulkasil

title: Silicon dioxide


text:
Nichols radiometer

A Nichols radiometer was the apparatus used by Ernest Fox Nichols and Gordon Ferrie Hull in 1901 for the measurement of radiation pressure.

It consisted of a pair of small silvered glass mirrors suspended in the manner of a torsion balance by a fine quartz fibre within an enclosure in which the air pressure could be regulated. The torsion head to which the fiber was attached could be turned from the outside using a magnet. A beam of light was directed first on one mirror and then on the other, and the opposite deflections observed with mirror and scale. By turning the mirror system around to receive the light on the unsilvered side, the influence of the air in the enclosure could be ascertained. This influence was found to be of almost negligible value at an air pressure of about 16 mmHg (2.1 kPa). The radiant energy of the incident beam was deduced from its heating effect upon a small blackened silver disk, which was found to be more reliable than the bolometer when it was first used. With this apparatus, the experimenters were able to obtain an agreement between observed and computed radiation pressures within about 0.6%.

The original apparatus is at the Smithsonian Institution.

This apparatus is sometimes confused with the Crookes radiometer of 1873.

The original papers, with their historical context, have been re-printed in a chapter of the book Quantum Photonics: Pioneering Advances and Emerging Applications.

title: Nichols radiometer