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The Battle of Villers-Bocage took place in Normandy, France, on 13 June 1944 during World War II. Following the D-Day landings on 6 June, the Germans established defences in front of Caen. The British attacked to attempt to exploit a gap in the German defences west of the city. They reached Villers-Bocage without incident in the morning but ...
The 2020 Summer Olympics, officially the Games of the XXXII Olympiad and officially branded as Tokyo 2020, were an international multi-sport event held from 23 July to 8 August 2021 in Tokyo, Japan, with some preliminary events that began on 21 July 2021.
Average human height by country. Below are two tables which report the average adult human height by country or geographical region. With regard to the first table, original studies and sources should be consulted for details on methodology and the exact populations measured, surveyed, or considered. With regard to the second table, these ...
- History
- Production
- Properties
- Processing
- Applications and Uses
- Safety
- Ecotoxicity
- Similar Polymers
- See Also
- Further Reading
Polytetrafluoroethylene (PTFE) was accidentally discovered in 1938 by Roy J. Plunkett while he was working in New Jersey for DuPont. As Plunkett attempted to make a new chlorofluorocarbon refrigerant, the tetrafluoroethylene gas in its pressure bottle stopped flowing before the bottle's weight had dropped to the point signaling "empty". Since Plunk...
PTFE is produced by free-radical polymerization of tetrafluoroethylene.The net equation is 1. n F2C=CF2 → −(F2C−CF2)n− Because tetrafluoroethylene can explosively decompose to tetrafluoromethane (CF4) and carbon, a special apparatus is required for the polymerization to prevent hot spots that might initiate this dangerous side reaction. The process...
PTFE is a thermoplastic polymer, which is a white solid at room temperature, with a density of about 2200 kg/m3 and a melting point of 600 K (327 °C; 620 °F). It maintains high strength, toughness and self-lubrication at low temperatures down to 5 K (−268.15 °C; −450.67 °F), and good flexibility at temperatures above 194 K (−79 °C; −110 °F). PTFE g...
Processing PTFE can be difficult and expensive, because the high melting temperature, 327 °C (621 °F), is above the decomposition temperature. Even when molten, PTFE does not flow due to its exceedingly high melt-viscosity. The viscosity and melting point can be decreased by inclusion of small amount of comonomers such as perfluoro (propylvinyl eth...
Wire insulation, electronics
The major application of PTFE, consuming about 50% of production, is for the insulation of wiring in aerospace and computer applications (e.g. hookup wire, coaxial cables). This application exploits the fact that PTFE has excellent dielectric properties, specifically low group velocity dispersion, especially at high radio frequencies, making it suitable for use as an excellent insulator in connector assemblies and cables, and in printed circuit boards used at microwave frequencies. Combined w...
Bearings seals
In industrial applications, owing to its low friction, PTFE is used for plain bearings, gears, slide plates, seals, gaskets, bushings, and more applications with sliding action of parts, where it outperforms acetal and nylon.
Electrets
Its extremely high bulk resistivity makes it an ideal material for fabricating long-life electrets, the electrostatic analogues of permanent magnets.
While PTFE is stable at lower temperatures, it begins to deteriorate at temperatures of about 260 °C (500 °F), it decomposes above 350 °C (662 °F), and pyrolysis occurs at temperatures above 400 °C (752 °F). The main decomposition products are fluorocarbon gases and a sublimate, including tetrafluoroethylene (TFE) and difluorocarbene radicals(RCF2)...
Trifluoroacetate
Sodium trifluoroacetate and the similar compound sodium chlorodifluoroacetate can both be generated when PTFE undergoes thermolysis, as well as producing longer chain polyfluoro- and/or polychlorofluoro- (C3-C14) carboxylic acids which may be equally persistent. These products can accumulate in evaporative wetlandsand have been found in the roots and seeds of wetland plant species, but has not been observed to have an adverse impact on plant health or germination success.
PFOA
Perfluorooctanoic acid (PFOA, or C8) has been used as a surfactant in the emulsion polymerizationof PTFE, although several manufacturers have entirely discontinued its use. PFOA persists indefinitely in the environment. PFOA has been detected in the blood of many individuals of the general US population in the low and sub-parts per billion range, and levels are higher in chemical plant employees and surrounding subpopulations. PFOA and perfluorooctanesulfonic acid (PFOS) have been estimated t...
GenX
As a result of the lawsuits concerning the PFOA class-action lawsuit, DuPont began to use GenX, a similarly fluorinated compound, as a replacement for perfluorooctanoic acid in the manufacture of fluoropolymers, such as Teflon-brand PTFE.However, in lab tests on rats, GenX has been shown to cause many of the same health problems as PFOA. The chemicals are manufactured by Chemours, a corporate spin-off of DuPont, in Fayetteville, North Carolina. Fayetteville Works was the site where DuPont beg...
The Teflon trade name is also used for other polymers with similar compositions: 1. Perfluoroalkoxy alkane(PFA) 2. Fluorinated ethylene propylene(FEP) These retain the useful PTFE properties of low friction and nonreactivity, but are also more easily formable. For example, FEP is softer than PTFE and melts at 533 K (260 °C; 500 °F); it is also high...
Ellis, D.A.; Mabury, S.A.; Martin, J.W.; Muir, D.C.G.; Mabury, S.A.; Martin, J.W.; Muir, D.C.G. (2001). "Thermolysis of fluoropolymers as a potential source of halogenated organic acids in the envi...
The Organisation for Economic Co-operation and Development (OECD; French: Organisation de coopération et de développement économiques, OCDE) is an intergovernmental organisation with 38 member countries,[1][4] founded in 1961 to stimulate economic progress and world trade. It is a forum whose member countries describe themselves as ...
Cyprus [f] ( / ˈsaɪprəs / ⓘ ), officially the Republic of Cyprus, [g] is an island country in the eastern Mediterranean Sea, north of the Sinai Peninsula, south of the Anatolian Peninsula, and west of the Levant. It is geographically a part of West Asia, but its cultural ties and geopolitics are overwhelmingly Southeast European.
Singapore, officially the Republic of Singapore, is an island country and city-state in maritime Southeast Asia.It is located about one degree of latitude (137 kilometres or 85 miles) north of the equator, off the southern tip of the Malay Peninsula, bordering the Strait of Malacca to the west, the Singapore Strait to the south along with the Riau Islands in Indonesia, the South China Sea to ...
