Polytetrafluoroethylene
Encyclopedia
Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer
of tetrafluoroethylene
that finds numerous applications. PTFE is most well known by the DuPont
brand name Teflon.
PTFE is a fluorocarbon
solid, as it is a high-molecular-weight compound consisting wholly of carbon
and fluorine
. PTFE is hydrophobic: neither water nor water-containing substances wet PTFE, as fluorocarbons demonstrate mitigated London dispersion force
s due to the high electronegativity
of fluorine. PTFE has one of the lowest coefficients of friction
against any solid.
PTFE is used as a non-stick coating for pans and other cookware. It is very non-reactive, partly because of the strength of carbon–fluorine bond
s, and so it is often used in containers and pipework for reactive and corrosive chemicals. Where used as a lubricant
, PTFE reduces friction, wear, and energy consumption of machinery.
It is commonly believed that teflon, like velcro
, is a spin-off product from the NASA
space projects. However, that is not so, even though both
products have been used by NASA.
in New Jersey in 1938. While Plunkett was attempting to make a new CFC
refrigerant, the tetrafluoroethylene
gas in its pressure bottle stopped flowing before the bottle's weight had dropped to the point signaling "empty." Since Plunkett was measuring the amount of gas used by weighing the bottle, he became curious as to the source of the weight, and finally resorted to sawing the bottle apart. Inside, he found it coated with a waxy white material which was oddly slippery. Analysis of the material showed that it was polymerized perfluoroethylene, with the iron from the inside of the container having acted as a catalyst at high pressure. Kinetic Chemicals patented the new fluorinated plastic (analogous to known polyethylene
) in 1941 and registered the Teflon trademark in 1945.
An early advanced use was in the Manhattan Project
as a material to coat valves and seals in the pipes holding highly reactive uranium hexafluoride
at the vast K-25
uranium enrichment
plant at Oak Ridge, Tennessee
.
DuPont, which founded Kinetic Chemicals in partnership with General Motors
, was producing over two million pounds (900 tons) of Teflon per year in Parkersburg, West Virginia
, by 1948.
In 1954, French engineer Marc Grégoire created the first pan coated with Teflon non-stick resin under the brand name of Tefal
after his wife urged him to try the material he had been using on fishing tackle on her cooking pans. In the United States, Kansas City, Missouri resident Marion A. Trozzolo
, who had been using the substance on scientific utensils, marketed the first US-made Teflon coated frying pan, "The Happy Pan," in 1961.
PTFE is a thermoplastic
polymer
, which is a white solid at room temperature, with a density of about 2.2 g/cm3. According to DuPont, its melting point is 327 °C (620.6 °F), but its mechanical properties degrade above 260 °C (500 °F). PTFE gains its properties from the aggregate effect of carbon-fluorine bonds, as do all fluorocarbons.
The coefficient of friction of plastics is usually measured against polished steel. PTFE's coefficient of friction is 0.05 to 0.10, which is the third-lowest of any known solid material (BAM
being the first, with a coefficient of friction of 0.02; diamond-like carbon
being second-lowest at 0.05). PTFE's resistance to van der Waals force
s means that it is the only known surface to which a gecko
cannot stick.
PTFE has excellent dielectric
properties. This is especially true at high radio frequencies
, making it suitable for use as an insulator
in cable
s and connector
assemblies and as a material for printed circuit board
s used at microwave
frequencies. Combined with its high melting temperature, this makes it the material of choice as a high-performance substitute for the weaker and lower melting point polyethylene
that is commonly used in low-cost applications.
Because of its chemical inertness, PTFE cannot be cross-linked like an elastomer
. Therefore, it has no "memory" and is subject to creep
. This is advantageous when used as a seal
, because the material creeps a small amount to conform to the mating surface. However, to keep the seal from creeping too much, fillers are used, which can also improve wear resistance and reduce friction. Sometimes, metal springs apply continuous force to PTFE seals to give good contact, while permitting a beneficially low percentage of creep.
s, gear
s, slide plate
s, etc. In these applications, it performs significantly better than nylon
and acetal
; it is comparable to ultra-high-molecular-weight polyethylene (UHMWPE), although UHMWPE is more resistant to wear than Teflon. For these applications, versions of Teflon with mineral oil or molybdenum disulfide
embedded as additional lubricant
s in its matrix are being manufactured.
Its extremely high bulk resistivity
makes it an ideal material for fabricating long-life electret
s, useful devices that are the electrostatic analogues of magnet
s.
Gore-Tex
is a material incorporating a fluoropolymer membrane with micropores. The roof of the Hubert H. Humphrey Metrodome
in Minneapolis is one of the largest applications of Teflon PTFE coatings, using 20 acres (80,937.2 m²) of the material in a double-layered, white dome, made with PTFE-coated fiberglass, that gives the stadium its distinctive appearance. The Millennium Dome
in London
is also made with a substantial use of PTFE coatings.
Powdered PTFE is used in pyrotechnic composition
s as oxidizers together with powdered metals such as aluminium
and magnesium
. Upon ignition, these mixtures form carbonaceous soot
and the corresponding metal fluoride
, and release large amounts of heat. Hence they are used as infrared decoy flares and igniters for solid-fuel rocket propellant
s.
In optical radiometry
, sheets made from PTFE are used as measuring heads in spectroradiometers and broadband radiometers (e.g., illuminance
meters and UV
radiometer
s) due to its capability to diffuse a transmitting light nearly perfectly. Moreover, optical properties of PTFE stay constant over a wide range of wavelengths, from UV up to near infrared
. In this region, the relation of its regular transmittance to diffuse transmittance is negligibly small, so light transmitted through a diffuser (PTFE sheet) radiates like Lambert's cosine law
. Thus, PTFE enables cosinusoidal angular response for a detector measuring the power of optical radiation at a surface, e.g., in solar irradiance
measurements.
PTFE is also used to coat certain types of hardened, armor-piercing bullets, so as to prevent the increased wear on the firearm's rifling that would result from the harder projectile, however it is not the PTFE itself that gives the bullet its armor-piercing property.
High corrosion resistance favors the use of PTFE in laboratory environments as containers, as magnetic stirrer coatings, and as tubing for highly corrosive chemicals such as hydrofluoric acid
, which will dissolve glass containers.
PTFE is also widely used as a thread seal tape
in plumbing applications, largely replacing paste thread dope.
PTFE membrane filters are among the most efficient used in industrial air filtration applications. Filter coated with a PTFE membrane are often used within a dust collection system
to collect particulate matter from air streams in applications involving high temperatures and high particulate loads such as coal-fired power plants, cement production, and steel foundries.
PTFE grafts can be used to bypass stenotic
arteries
in peripheral vascular disease, if a suitable autologous vein
graft is not available.
PTFE can be used to prevent insects climbing up surfaces painted with the material. PTFE is so slippery that insects cannot get a grip and tend to fall off. For example, PTFE is used to prevent ants climbing out of formicaria
.
of PTFE is detectable at 200 °C (392 °F), and it evolves several fluorocarbon
gases and a sublimate. Animal studies indicate that it is unlikely that these products would be generated in amounts significant to health at temperatures below 250 °C (482 °F), although birds are proven to be much more sensitive to these decomposition products.
While PTFE is stable and nontoxic, it begins to deteriorate after the temperature of cookware reaches about 260 °C (500 °F), and decomposes above 350 °C (662 °F). These degradation by-products can be lethal to bird
s, and can cause flu-like symptoms in humans.
Meat is usually fried between 200 and, and most oils will start to smoke before a temperature of 260 °C is reached, but there are at least two cooking oils (refined safflower oil and avocado oil
) that have a higher smoke point
than 260 °C. Empty cookware can also exceed this temperature upon heating.
(PFOA or C8), in the form of the ammonium salt, is used as a surfactant
in the emulsion polymerization
of PTFE, and has been detected in some PTFE products. The levels that have been measured in nonstick cookware range from not detectable to 75 parts per billion. These are lower than in PTFE products such as thread sealant tape (with 1800 parts per billion (1.8 parts per million) of PFOA detected) because nonstick cookware is heated to volatilize PFOA.
A DuPont study on Teflon PTFE did not detect any PFOA above their detection limit
of 9 parts per billion, and DuPont says no PFOA is in Teflon cookware. A 2009 USEPA study found levels of PFOA in nonstick cookware ranging from undetected (with a detection limit of 1.5 parts per billion) to 4.3 parts per billion. DuPont says there should be no measurable amount on a finished pan provided it has been properly cured
. While PFOA has been detected in the low parts per billion range in the blood of people, exposure from nonstick cookware is considered insignificant—despite the marketing of other wares. However, at temperatures well above those encountered in cooking, PTFE pyrolysis can form minor amounts of PFOA.
In January 2006, DuPont, the only company that manufactures PFOA in the US, agreed to eliminate releases of the chemical from its manufacturing plants by 2015, but did not commit to completely phasing out its use of the chemical. In the emulsion polymerization of PTFE, 3M subsidiary Dyneon has developed a replacement emulsifier despite DuPont stating that PFOA is an "essential processing aid". As of August 2008, the EPA's position was that it "has no information that routine use of household or other products using fluoropolymers, such as nonstick cookware or all weather clothing, poses a concern."
Other polymers with similar composition are also known by the Teflon trade name:
They retain the useful properties of PTFE of low friction and nonreactivity, but are more easily formable. For example, FEP is softer than PTFE and melts at 260 °C (500 °F); it is also highly transparent and resistant to sunlight.
Fluoropolymer
A fluoropolymer is a fluorocarbon based polymer with multiple strong carbon–fluorine bonds. It is characterized by a high resistance to solvents, acids, and bases.-History:Fluoropolymers were accidentally discovered in 1938 by Dr. Roy J...
of tetrafluoroethylene
Tetrafluoroethylene
Tetrafluoroethylene is a chemical compound with the formula C2F4. It is the simplest alkene fluorocarbon. This gaseous species is used primarily in the industrial preparation of polymers.-Properties:...
that finds numerous applications. PTFE is most well known by the DuPont
DuPont
E. I. du Pont de Nemours and Company , commonly referred to as DuPont, is an American chemical company that was founded in July 1802 as a gunpowder mill by Eleuthère Irénée du Pont. DuPont was the world's third largest chemical company based on market capitalization and ninth based on revenue in 2009...
brand name Teflon.
PTFE is a fluorocarbon
Fluorocarbon
Fluorocarbons, sometimes referred to as perfluorocarbons or PFCs, are organofluorine compounds that contain only carbon and fluorine bonded together in strong carbon–fluorine bonds. Fluoroalkanes that contain only single bonds are more chemically and thermally stable than alkanes...
solid, as it is a high-molecular-weight compound consisting wholly of carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
and fluorine
Fluorine
Fluorine is the chemical element with atomic number 9, represented by the symbol F. It is the lightest element of the halogen column of the periodic table and has a single stable isotope, fluorine-19. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic...
. PTFE is hydrophobic: neither water nor water-containing substances wet PTFE, as fluorocarbons demonstrate mitigated London dispersion force
London dispersion force
London dispersion forces is a type of force acting between atoms and molecules. They are part of the van der Waals forces...
s due to the high electronegativity
Electronegativity
Electronegativity, symbol χ , is a chemical property that describes the tendency of an atom or a functional group to attract electrons towards itself. An atom's electronegativity is affected by both its atomic number and the distance that its valence electrons reside from the charged nucleus...
of fluorine. PTFE has one of the lowest coefficients of friction
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...
against any solid.
PTFE is used as a non-stick coating for pans and other cookware. It is very non-reactive, partly because of the strength of carbon–fluorine bond
Carbon–fluorine bond
The carbon–fluorine bond is a bond between carbon and fluorine that is a component of all organofluorine compounds. It is the strongest single bond in organic chemistry—and relatively short—due to its partial ionic character. The bond also strengthens and shortens as more fluorines are...
s, and so it is often used in containers and pipework for reactive and corrosive chemicals. Where used as a lubricant
Lubricant
A lubricant is a substance introduced to reduce friction between moving surfaces. It may also have the function of transporting foreign particles and of distributing heat...
, PTFE reduces friction, wear, and energy consumption of machinery.
It is commonly believed that teflon, like velcro
Velcro
Velcro is the brand name of the first commercially marketed fabric hook-and-loop fastener, invented in 1948 by the Swiss electrical engineer George de Mestral...
, is a spin-off product from the NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
space projects. However, that is not so, even though both
products have been used by NASA.
History
PTFE was accidentally invented by Roy Plunkett of Kinetic ChemicalsKinetic Chemicals
Kinetic Chemicals Inc. was a joint venture between DuPont and General Motors. It was founded in 1930 to develop and commercialize chlorofluorocarbon chemicals, such as refrigerants. One of the more famous inventions of Kinetic Chemicals was Teflon. In 1949, the operations came under control of...
in New Jersey in 1938. While Plunkett was attempting to make a new CFC
Chlorofluorocarbon
A chlorofluorocarbon is an organic compound that contains carbon, chlorine, and fluorine, produced as a volatile derivative of methane and ethane. A common subclass are the hydrochlorofluorocarbons , which contain hydrogen, as well. They are also commonly known by the DuPont trade name Freon...
refrigerant, the tetrafluoroethylene
Tetrafluoroethylene
Tetrafluoroethylene is a chemical compound with the formula C2F4. It is the simplest alkene fluorocarbon. This gaseous species is used primarily in the industrial preparation of polymers.-Properties:...
gas in its pressure bottle stopped flowing before the bottle's weight had dropped to the point signaling "empty." Since Plunkett was measuring the amount of gas used by weighing the bottle, he became curious as to the source of the weight, and finally resorted to sawing the bottle apart. Inside, he found it coated with a waxy white material which was oddly slippery. Analysis of the material showed that it was polymerized perfluoroethylene, with the iron from the inside of the container having acted as a catalyst at high pressure. Kinetic Chemicals patented the new fluorinated plastic (analogous to known polyethylene
Polyethylene
Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...
) in 1941 and registered the Teflon trademark in 1945.
An early advanced use was in the Manhattan Project
Manhattan Project
The Manhattan Project was a research and development program, led by the United States with participation from the United Kingdom and Canada, that produced the first atomic bomb during World War II. From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the US Army...
as a material to coat valves and seals in the pipes holding highly reactive uranium hexafluoride
Uranium hexafluoride
Uranium hexafluoride , referred to as "hex" in the nuclear industry, is a compound used in the uranium enrichment process that produces fuel for nuclear reactors and nuclear weapons. It forms solid grey crystals at standard temperature and pressure , is highly toxic, reacts violently with water...
at the vast K-25
K-25
K-25 is a former uranium enrichment facility of the Manhattan Project which used the gaseous diffusion method. The plant is located in Oak Ridge, Tennessee, on the southwestern end of the Oak Ridge Reservation.-History:...
uranium enrichment
Enriched uranium
Enriched uranium is a kind of uranium in which the percent composition of uranium-235 has been increased through the process of isotope separation. Natural uranium is 99.284% 238U isotope, with 235U only constituting about 0.711% of its weight...
plant at Oak Ridge, Tennessee
Oak Ridge, Tennessee
Oak Ridge is a city in Anderson and Roane counties in the eastern part of the U.S. state of Tennessee, about west of Knoxville. Oak Ridge's population was 27,387 at the 2000 census...
.
DuPont, which founded Kinetic Chemicals in partnership with General Motors
General Motors
General Motors Company , commonly known as GM, formerly incorporated as General Motors Corporation, is an American multinational automotive corporation headquartered in Detroit, Michigan and the world's second-largest automaker in 2010...
, was producing over two million pounds (900 tons) of Teflon per year in Parkersburg, West Virginia
Parkersburg, West Virginia
As of the census of 2000, there were 33,099 people, 14,467 households, and 8,767 families residing in the city. In 2006 the U.S. Census Bureau estimated that Parkersburg's population had decreased 4.4% to 31,755. The population density was 2,800.5 people per square mile . There were 16,100 housing...
, by 1948.
In 1954, French engineer Marc Grégoire created the first pan coated with Teflon non-stick resin under the brand name of Tefal
Tefal
Tefal is a French cookware and small appliance manufacturer owned by Groupe SEB. Its name is a portmanteau of the words TEFlon and ALuminium.Tefal is known for creating the non-stick cookware category....
after his wife urged him to try the material he had been using on fishing tackle on her cooking pans. In the United States, Kansas City, Missouri resident Marion A. Trozzolo
Marion A. Trozzolo
Marion A. Trozzolo was a pioneer, visionary, innovator, inventor, entrepreneur, and professor of business at Rockhurst University in Kansas City, Missouri...
, who had been using the substance on scientific utensils, marketed the first US-made Teflon coated frying pan, "The Happy Pan," in 1961.
Properties
Thermoplastic
Thermoplastic, also known as a thermosoftening plastic, is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently...
polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
, which is a white solid at room temperature, with a density of about 2.2 g/cm3. According to DuPont, its melting point is 327 °C (620.6 °F), but its mechanical properties degrade above 260 °C (500 °F). PTFE gains its properties from the aggregate effect of carbon-fluorine bonds, as do all fluorocarbons.
| Property | Value |
|---|---|
| Density | 2200 kg/m3 |
| Melting point Melting point The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure... |
327 °C |
| 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... |
0.5 GPa |
| Yield strength | 23 MPa |
| Coefficient of friction | 0.05–0.10 |
| 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... |
ε=2.1,tan(δ)<5(-4) |
| Dielectric constant (60 Hz) | ε=2.1,tan(δ)<2(-4) |
| 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.... (1 MHz) |
60 MV/m |
The coefficient of friction of plastics is usually measured against polished steel. PTFE's coefficient of friction is 0.05 to 0.10, which is the third-lowest of any known solid material (BAM
Aluminium magnesium boride
Aluminium magnesium boride , also known as BAM, is a chemical compound of aluminium, magnesium and boron, and is a ceramic alloy that is highly resistive to wear with a low coefficient of sliding friction...
being the first, with a coefficient of friction of 0.02; diamond-like carbon
Diamond-like carbon
Diamond-like carbon exists in seven different forms of amorphous carbon materials that display some of the typical properties of diamond. They are usually applied as coatings to other materials that could benefit from some of those properties. All seven contain significant amounts of sp3...
being second-lowest at 0.05). PTFE's resistance to van der Waals force
Van der Waals force
In physical chemistry, the van der Waals force , named after Dutch scientist Johannes Diderik van der Waals, is the sum of the attractive or repulsive forces between molecules other than those due to covalent bonds or to the electrostatic interaction of ions with one another or with neutral...
s means that it is the only known surface to which a gecko
Gecko
Geckos are lizards belonging to the infraorder Gekkota, found in warm climates throughout the world. They range from 1.6 cm to 60 cm....
cannot stick.
PTFE has excellent dielectric
Dielectric
A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...
properties. This is especially true at high radio frequencies
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
, making it suitable for use as an insulator
Electrical insulation
thumb|250px|[[Coaxial Cable]] with dielectric insulator supporting a central coreThis article refers to electrical insulation. For insulation of heat, see Thermal insulation...
in cable
Cable
A cable is two or more wires running side by side and bonded, twisted or braided together to form a single assembly. In mechanics cables, otherwise known as wire ropes, are used for lifting, hauling and towing or conveying force through tension. In electrical engineering cables are used to carry...
s and connector
Electrical connector
An electrical connector is an electro-mechanical device for joining electrical circuits as an interface using a mechanical assembly. The connection may be temporary, as for portable equipment, require a tool for assembly and removal, or serve as a permanent electrical joint between two wires or...
assemblies and as a material for printed circuit board
Printed circuit board
A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...
s used at microwave
Microwave
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
frequencies. Combined with its high melting temperature, this makes it the material of choice as a high-performance substitute for the weaker and lower melting point polyethylene
Polyethylene
Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...
that is commonly used in low-cost applications.
Because of its chemical inertness, PTFE cannot be cross-linked like an elastomer
Elastomer
An elastomer is a polymer with the property of viscoelasticity , generally having notably low Young's modulus and high yield strain compared with other materials. The term, which is derived from elastic polymer, is often used interchangeably with the term rubber, although the latter is preferred...
. Therefore, it has no "memory" and is subject to creep
Creep (deformation)
In materials science, creep is the tendency of a solid material to slowly move or deform permanently under the influence of stresses. It occurs as a result of long term exposure to high levels of stress that are below the yield strength of the material....
. This is advantageous when used as a seal
Seal (mechanical)
A mechanical seal is a device which helps join systems or mechanisms together by preventing leakage , containing pressure, or excluding contamination...
, because the material creeps a small amount to conform to the mating surface. However, to keep the seal from creeping too much, fillers are used, which can also improve wear resistance and reduce friction. Sometimes, metal springs apply continuous force to PTFE seals to give good contact, while permitting a beneficially low percentage of creep.
Applications and uses
Owing to its low friction, it is used for applications where sliding action of parts is needed: plain bearingPlain bearing
A plain bearing, also known as a plane bearing or a friction bearing is the simplest type of bearing, comprising just a bearing surface and no rolling elements. Therefore the journal slides over the bearing surface. The simplest example of a plain bearing is a shaft rotating in a hole...
s, gear
Gear
A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine....
s, slide plate
Slide plate
A slide plate is linear bearing such as may be part of the expansion joints of bridges, high temperature horizontal ducts of water-tube boilers and other mechanical or structural engineering applications...
s, etc. In these applications, it performs significantly better than nylon
Nylon
Nylon is a generic designation for a family of synthetic polymers known generically as polyamides, first produced on February 28, 1935, by Wallace Carothers at DuPont's research facility at the DuPont Experimental Station...
and acetal
Polyoxymethylene
Polyoxymethylene , also known as acetal, polyacetal, and polyformaldehyde, is an engineering thermoplastic used in precision parts that require high stiffness, low friction and excellent dimensional stability....
; it is comparable to ultra-high-molecular-weight polyethylene (UHMWPE), although UHMWPE is more resistant to wear than Teflon. For these applications, versions of Teflon with mineral oil or molybdenum disulfide
Molybdenum disulfide
Molybdenum disulfide is the inorganic compound with the formula MoS2. This black crystalline sulfide of molybdenum occurs as the mineral molybdenite. It is the principal ore from which molybdenum metal is extracted. The natural amorphous form is known as the rarer mineral jordisite. MoS2 is less...
embedded as additional lubricant
Lubricant
A lubricant is a substance introduced to reduce friction between moving surfaces. It may also have the function of transporting foreign particles and of distributing heat...
s in its matrix are being manufactured.
Its extremely high bulk resistivity
Resistivity
Electrical resistivity is a measure of how strongly a material opposes the flow of electric current. A low resistivity indicates a material that readily allows the movement of electric charge. The SI unit of electrical resistivity is the ohm metre...
makes it an ideal material for fabricating long-life electret
Electret
Electret is a dielectric material that has a quasi-permanent electric charge or dipole polarisation. An electret generates internal and external electric fields, and is the electrostatic equivalent of a permanent magnet. Oliver Heaviside coined this term in 1885...
s, useful devices that are the electrostatic analogues of magnet
Magnet
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.A permanent magnet is an object...
s.
Gore-Tex
Gore-Tex
Gore-Tex is a waterproof/breathable fabric, and a registered trademark of W. L. Gore and Associates. It was co-invented by Wilbert L. Gore, Rowena Taylor, and Gore's son, Robert W. Gore. Robert Gore was granted on April 27, 1976, for a porous form of polytetrafluoroethylene with a...
is a material incorporating a fluoropolymer membrane with micropores. The roof of the Hubert H. Humphrey Metrodome
Hubert H. Humphrey Metrodome
The Hubert H. Humphrey Metrodome, commonly called the Metrodome, is a domed sports stadium in downtown Minneapolis, Minnesota, United States. Opened in 1982, it replaced Metropolitan Stadium, which was on the current site of the Mall of America in Bloomington and Memorial Stadium on the University...
in Minneapolis is one of the largest applications of Teflon PTFE coatings, using 20 acres (80,937.2 m²) of the material in a double-layered, white dome, made with PTFE-coated fiberglass, that gives the stadium its distinctive appearance. The Millennium Dome
Millennium Dome
The Millennium Dome, colloquially referred to simply as The Dome or even The O2 Arena, is the original name of a large dome-shaped building, originally used to house the Millennium Experience, a major exhibition celebrating the beginning of the third millennium...
in London
London
London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...
is also made with a substantial use of PTFE coatings.
Powdered PTFE is used in pyrotechnic composition
Pyrotechnic composition
A pyrotechnic composition is a substance or mixture of substances designed to produce an effect by heat, light, sound, gas or smoke or a combination of these, as a result of non-detonative self-sustaining exothermic chemical reactions...
s as oxidizers together with powdered metals such as 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 magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
. Upon ignition, these mixtures form carbonaceous soot
Soot
Soot is a general term that refers to impure carbon particles resulting from the incomplete combustion of a hydrocarbon. It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the residual pyrolyzed fuel particles such as cenospheres,...
and the corresponding metal fluoride
Fluoride
Fluoride is the anion F−, the reduced form of fluorine when as an ion and when bonded to another element. Both organofluorine compounds and inorganic fluorine containing compounds are called fluorides. Fluoride, like other halides, is a monovalent ion . Its compounds often have properties that are...
, and release large amounts of heat. Hence they are used as infrared decoy flares and igniters for solid-fuel rocket propellant
Propellant
A propellant is a material that produces pressurized gas that:* can be directed through a nozzle, thereby producing thrust ;...
s.
In optical radiometry
Radiometry
In optics, radiometry is a set of techniques for measuring electromagnetic radiation, including visible light. Radiometric techniques characterize the distribution of the radiation's power in space, as opposed to photometric techniques, which characterize the light's interaction with the human eye...
, sheets made from PTFE are used as measuring heads in spectroradiometers and broadband radiometers (e.g., illuminance
Illuminance
In photometry, illuminance is the total luminous flux incident on a surface, per unit area. It is a measure of the intensity of the incident light, wavelength-weighted by the luminosity function to correlate with human brightness perception. Similarly, luminous emittance is the luminous flux per...
meters and UV
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...
radiometer
Radiometer
A radiometer is a device for measuring the radiant flux of electromagnetic radiation. Generally, the term radiometer denotes an infrared radiation detector, yet it also includes detectors operating on any electromagnetic wavelength....
s) due to its capability to diffuse a transmitting light nearly perfectly. Moreover, optical properties of PTFE stay constant over a wide range of wavelengths, from UV up to near 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...
. In this region, the relation of its regular transmittance to diffuse transmittance is negligibly small, so light transmitted through a diffuser (PTFE sheet) radiates like Lambert's cosine law
Lambert's cosine law
In optics, Lambert's cosine law says that the radiant intensity observed from a Lambertian surface or a Lambertian radiator is directly proportional to the cosine of the angle θ between the observer's line of sight and the surface normal. A Lambertian surface is also known as an ideal diffusely...
. Thus, PTFE enables cosinusoidal angular response for a detector measuring the power of optical radiation at a surface, e.g., in solar irradiance
Irradiance
Irradiance is the power of electromagnetic radiation per unit area incident on a surface. Radiant emittance or radiant exitance is the power per unit area radiated by a surface. The SI units for all of these quantities are watts per square meter , while the cgs units are ergs per square centimeter...
measurements.
PTFE is also used to coat certain types of hardened, armor-piercing bullets, so as to prevent the increased wear on the firearm's rifling that would result from the harder projectile, however it is not the PTFE itself that gives the bullet its armor-piercing property.
High corrosion resistance favors the use of PTFE in laboratory environments as containers, as magnetic stirrer coatings, and as tubing for highly corrosive chemicals such as 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 will dissolve glass containers.
PTFE is also widely used as a thread seal tape
Thread seal tape
Thread seal tape, or teflon tape can be used in many ways, the most common use in America is to seal things. Thread seal tape — commonly known as "Teflon tape", "PTFE tape", "tape dope", or "plumber's tape"–is a polytetrafluoroethylene film cut to specified widths for use in sealing pipe...
in plumbing applications, largely replacing paste thread dope.
PTFE membrane filters are among the most efficient used in industrial air filtration applications. Filter coated with a PTFE membrane are often used within a dust collection system
Dust collection system
A dust collection system is an air quality improvement system used in industrial, commercial, and home production shops to improve breathable air quality and safety by removing particulate matter from the air and environment. Dust collection systems work on the basic formula of CAPTURE, CONVEY and...
to collect particulate matter from air streams in applications involving high temperatures and high particulate loads such as coal-fired power plants, cement production, and steel foundries.
PTFE grafts can be used to bypass stenotic
Stenosis
A stenosis is an abnormal narrowing in a blood vessel or other tubular organ or structure.It is also sometimes called a stricture ....
arteries
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....
in peripheral vascular disease, if a suitable autologous vein
Vein
In the circulatory system, veins are blood vessels that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood to the heart...
graft is not available.
PTFE can be used to prevent insects climbing up surfaces painted with the material. PTFE is so slippery that insects cannot get a grip and tend to fall off. For example, PTFE is used to prevent ants climbing out of formicaria
Formicarium
A formicarium or ant farm is a vivarium which is designed primarily for the study of ant colonies and how ants behave. Those who study ant behavior are known as myrmecologists.-History:...
.
Safety
The pyrolysisPyrolysis
Pyrolysis is a thermochemical decomposition of organic material at elevated temperatures without the participation of oxygen. It involves the simultaneous change of chemical composition and physical phase, and is irreversible...
of PTFE is detectable at 200 °C (392 °F), and it evolves several fluorocarbon
Fluorocarbon
Fluorocarbons, sometimes referred to as perfluorocarbons or PFCs, are organofluorine compounds that contain only carbon and fluorine bonded together in strong carbon–fluorine bonds. Fluoroalkanes that contain only single bonds are more chemically and thermally stable than alkanes...
gases and a sublimate. Animal studies indicate that it is unlikely that these products would be generated in amounts significant to health at temperatures below 250 °C (482 °F), although birds are proven to be much more sensitive to these decomposition products.
While PTFE is stable and nontoxic, it begins to deteriorate after the temperature of cookware reaches about 260 °C (500 °F), and decomposes above 350 °C (662 °F). These degradation by-products can be lethal to bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s, and can cause flu-like symptoms in humans.
Meat is usually fried between 200 and, and most oils will start to smoke before a temperature of 260 °C is reached, but there are at least two cooking oils (refined safflower oil and avocado oil
Avocado oil
Avocado oil is an edible oil pressed from the fruit of the Persea americana . As a food oil, it is used as an ingredient in other dishes, and as a cooking oil. It is also used for lubrication and in cosmetics where it is valued for its regenerative and moisturizing properties.It has an unusually...
) that have a higher smoke point
Smoke point
The smoke point generally refers to the temperature at which a cooking fat or oil begins to break down to glycerol and free fatty acids, and produce bluish smoke. The glycerol is then further broken down to acrolein which is a component of the smoke. It is the presence of the acrolein that causes...
than 260 °C. Empty cookware can also exceed this temperature upon heating.
PFOA
Perfluorooctanoic acidPerfluorooctanoic acid
Perfluorooctanoic acid , also known as C8 and perfluorooctanoate, is a synthetic, stable perfluorinated carboxylic acid and fluorosurfactant. One industrial application is as a surfactant in the emulsion polymerization of fluoropolymers. It has been used in the manufacture of such prominent...
(PFOA or C8), in the form of the ammonium salt, is used as a surfactant
Surfactant
Surfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid...
in the emulsion polymerization
Emulsion polymerization
Emulsion polymerization is a type of radical polymerization that usually starts with an emulsion incorporating water, monomer, and surfactant. The most common type of emulsion polymerization is an oil-in-water emulsion, in which droplets of monomer are emulsified in a continuous phase of water...
of PTFE, and has been detected in some PTFE products. The levels that have been measured in nonstick cookware range from not detectable to 75 parts per billion. These are lower than in PTFE products such as thread sealant tape (with 1800 parts per billion (1.8 parts per million) of PFOA detected) because nonstick cookware is heated to volatilize PFOA.
A DuPont study on Teflon PTFE did not detect any PFOA above their detection limit
Detection limit
In analytical chemistry, the detection limit, lower limit of detection, or LOD , is the lowest quantity of a substance that can be distinguished from the absence of that substance within a stated confidence limit...
of 9 parts per billion, and DuPont says no PFOA is in Teflon cookware. A 2009 USEPA study found levels of PFOA in nonstick cookware ranging from undetected (with a detection limit of 1.5 parts per billion) to 4.3 parts per billion. DuPont says there should be no measurable amount on a finished pan provided it has been properly cured
Curing (chemistry)
Curing is a term in polymer chemistry and process engineering that refers to the toughening or hardening of a polymer material by cross-linking of polymer chains, brought about by chemical additives, ultraviolet radiation, electron beam or heat...
. While PFOA has been detected in the low parts per billion range in the blood of people, exposure from nonstick cookware is considered insignificant—despite the marketing of other wares. However, at temperatures well above those encountered in cooking, PTFE pyrolysis can form minor amounts of PFOA.
In January 2006, DuPont, the only company that manufactures PFOA in the US, agreed to eliminate releases of the chemical from its manufacturing plants by 2015, but did not commit to completely phasing out its use of the chemical. In the emulsion polymerization of PTFE, 3M subsidiary Dyneon has developed a replacement emulsifier despite DuPont stating that PFOA is an "essential processing aid". As of August 2008, the EPA's position was that it "has no information that routine use of household or other products using fluoropolymers, such as nonstick cookware or all weather clothing, poses a concern."
Similar polymers
- PerfluoroalkoxyPerfluoroalkoxyPerfluoroalkoxy or PFA is a type of fluoropolymer with properties similar to polytetrafluoroethylene . It differs from the PTFE resins in that it is melt-processable using conventional injection molding and screw extrusion techniques....
(PFA) - Fluorinated ethylene propyleneFluorinated ethylene propyleneFluorinated ethylene propylene or FEP is a copolymer of hexafluoropropylene and tetrafluoroethylene. It differs from the PTFE resins in that it is melt-processible using conventional injection molding and screw extrusion techniques. Fluorinated ethylene propylene was invented by DuPont and is sold...
(FEP)
They retain the useful properties of PTFE of low friction and nonreactivity, but are more easily formable. For example, FEP is softer than PTFE and melts at 260 °C (500 °F); it is also highly transparent and resistant to sunlight.
See also
- Magnesium/Teflon/VitonMagnesium/Teflon/VitonMagnesium/Teflon/Viton is a pyrolant. Teflon and Viton are trademarks of DuPont for polytetrafluoroethylene, n, and vinylidenfluoride-hexafluoroisopropene-copolymer, nn.-History:...
- Polymer adsorptionPolymer adsorptionAdsorption is the adhesion of ions or molecules onto the surface of another phase. Adsorption may occur via physisorption and chemisorption. Ions and molecules can adsorb to many types of surfaces including polymer surfaces. A polymer is a large molecule composed of repeating subunits bound...
- Polymer fume feverPolymer fume feverPolymer fume fever or fluoropolymer fever, also informally called Teflon flu, is an inhalation fever caused by the fumes released when Polytetrafluoroethylene is heated to between 300 °C and 450 °C. When PTFE is heated above 450 °C the pyrolysis products are different and inhalation may cause...
- BS 4994 PTFE as a thermoplastic lining for dual laminate chemical process plant equipment
External links
- EPA: Compound in Teflon may cause cancer http://www.msnbc.msn.com/id/8404384, Tom Costello, NBC News, 29 June 2005. (Flash video required)
- Plasma Processes and Adhesive Bonding of Polytetrafluoroethylene
- Fluoropolymer Comparison – Typical Properties DuPont
- Spanish applicator of fluoropolymers
- The Skinny On... Why Teflon Sticks to the Pan by Hannah Holmes at discovery.com.