Polytetrafluoroethylene is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. The well-known brand name of PTFE-based formulas is Teflon by Chemours. Chemours was a spin-off from DuPont, which discovered the compound in 1938. Another popular brand name of PTFE is Syncolon by Synco Chemical Corporation. 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 forces due to the high electronegativity of fluorine. PTFE has one of the lowest coefficients of friction of any solid. PTFE is used as a non-stick coating for other cookware, it is nonreactive because of the strength of carbon–fluorine bonds, so it is used in containers and pipework for reactive and corrosive chemicals. Where used as a lubricant, PTFE reduces friction and energy consumption of machinery, it is used as a graft material in surgical interventions.
It is frequently employed as coating on catheters. 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 Plunkett was measuring the amount of gas used by weighing the bottle, he became curious as to the source of the weight, resorted to sawing the bottle apart. He found the bottle's interior coated with a waxy white material, oddly slippery. Analysis 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 in 1941, registered the Teflon trademark in 1945. By 1948, DuPont, which founded Kinetic Chemicals in partnership with General Motors, was producing over two million pounds of Teflon brand PTFE per year in Parkersburg, West Virginia.
An early use was in the Manhattan Project as a material to coat valves and seals in the pipes holding reactive uranium hexafluoride at the vast K-25 uranium enrichment plant in Oak Ridge, Tennessee. In 1954, Collette Grégoire, the wife of French engineer Marc Grégoire, urged him to try the material he had been using on fishing tackle on her cooking pans, he subsequently created the first non-stick pans under the brandname Tefal. In the United States, Marion A. Trozzolo, using the substance on scientific utensils, marketed the first US-made PTFE-coated pan, "The Happy Pan", in 1961. Non-stick cookware has since become a common household product, nowadays offered by hundreds of manufacturers across the world. In the 1990s, it was found that PTFE could be radiation cross-linked above its melting point in an oxygen-free environment. Electron beam processing is one example of radiation processing. Cross-linked PTFE has improved radiation stability; this was significant because, for many years, irradiation at ambient conditions has been used to break down PTFE for recycling.
This radiation-induced chain scission allows it to be more reground and reused. PTFE is produced by free-radical polymerization of tetrafluoroethylene; the net equation is n F2C=CF2 → −n−Because tetrafluoroethylene can explosively decompose to tetrafluoromethane and carbon, special apparatus is required for the polymerization to prevent hot spots that might initiate this dangerous side reaction. The process is initiated with persulfate, which homolyzes to generate sulfate radicals: 2− ⇌ 2 SO4•−The resulting polymer is terminated with sulfate ester groups, which can be hydrolyzed to give OH end-groups; because PTFE is poorly soluble in all solvents, the polymerization is conducted as an emulsion in water. This process gives a suspension of polymer particles. Alternatively, the polymerization is conducted using a surfactant such as PFOS. PTFE is a thermoplastic polymer, a white solid at room temperature, with a density of about 2200 kg/m3. According to research, its melting point is 600 K, it maintains high strength and self-lubrication at low temperatures down to 5 K, good flexibility at temperatures above 194 K. PTFE gains its properties from the aggregate effect of carbon-fluorine bonds, as do all fluorocarbons.
The only chemicals known to affect these carbon-fluorine bonds are reactive metals like the alkali metals, at higher temperatures such metals as aluminium and magnesium, fluorinating agents such as xenon difluoride and cobalt fluoride. At temperatures above 650–700 °C PTFE will undergo depolymerization; the coefficient of friction of plastics is measured against polished steel. PTFE's coefficient of friction is 0.05 to 0.10, the third-lowest of any known solid material. PTFE's resistance to van der Waals forces means that it is the only known surface to which a gecko cannot stick. In fact, PTFE can be used to prevent insects climbing up surfaces painted with the material. PTFE is so slippery that insects tend to fall off. For example, PTFE is used to prevent ants climbing out of formicaria; because of its chemical inertness, PTFE cannot
José Peñarroya Peñarroya was a Spanish cartoonist of the Bruguera School, creator of famous characters such as Don Pío or Gordito Relleno. He was, alongside Cifré, the "official" cover artist of many of the publications of the house, until well into the 1960s; as a result, he is considered one of the "Big Five" of that editorial of the 1950s, along with Conti, Escobar and Cifré. During the Spanish Civil War he was a combatant in the republican army. After the war he left his job as an accountant for the study Estudios Chamartín, where he participated in the creation of several short films. In 1947 he began collaborating with Editorial Bruguera, for which he created Don Pío, Gordito Relleno and Don Berrinche, he was involved in several magazines of the publisher Pulgarcito and El DDT. At this time, he worked with his friends Escobar in a rented studio, they liked to catch red pine mushrooms in joke about it among themselves. In 1957, together with these and other cartoonist of Bruguera, Carlos Conti and Eugenio Giner, he created an independent company that began publishing a new journal, Tío Vivo, keeping the typical schemes of Bruguera magazines.
For this magazine, Peñarroya draw new characters, such as La familia Pi After the economic failure of Tío Vivo, he returned to Bruguera, for which continued creating characters, such as Floripondia Piripí, Pepe, el hincha, Pitagorín and Rudesindo el bucanero. He created new series for the magazine "Tele Chico". Peñarroya graphic style evolved over the years toward greater statism, abandoning kinetic curves and symbols. An author of a generation, Joan March described Peñarroya humor as more subtle, but more poetic than other authors of Bruguera. Peñarroya in Lambiek comiclopedia
Marshall Kirk McKusick is a computer scientist, known for his extensive work on BSD UNIX, from the 1980s to FreeBSD in the present day. He was president of the USENIX Association from 1990 to 1992 and again from 2002 to 2004, still serves on the board, he is on the editorial board of ACM Queue Magazine. He is known to friends and colleagues as "Kirk". McKusick received his B. S. in electrical engineering from Cornell University, 2 M. S. degrees and a Ph. D. in computer science from the University of California, Berkeley in 1984. McKusick is gay and lives in California with Eric Allman, his domestic partner since graduate school and whom he married in October, 2013. McKusick started with BSD by virtue of the fact that he shared an office at Berkeley with Bill Joy, who spearheaded the beginnings of the BSD system; some of his largest contributions to BSD have been to the file system. He helped to design the original Berkeley Fast File System. In the late 1990s, he implemented soft updates, an alternative approach to maintaining disk integrity after a crash or power outage, in FFS, a revised version of Unix File System known as "UFS2".
The magic number used in the UFS2 super block structure reflects McKusick's birth date: #define FS_UFS2_MAGIC 0x19540119. It is included as an easter egg, he was primarily responsible for creating the complementary features of filesystem snapshots and background fsck, which both integrate with soft updates. After the filesystem snapshot, the filesystem can be brought up after a power outage, fsck can run as a background process; the Design and Implementation series of books are regarded as high-quality works in computer science. They have been influential in the development of the BSD descendants; the BSD Daemon used to identify BSD, is copyrighted by Marshall Kirk McKusick. S. Leffler, M. McKusick, M. Karels, J. Quarterman: The Design and Implementation of the 4.3BSD UNIX Operating System, Addison-Wesley, January 1989, ISBN 0-201-06196-1. German translation published June 1990, ISBN 3-89319-239-5. Japanese translation published June 1991, ISBN 4-621-03607-6. S. Leffler, M. McKusick: The Design and Implementation of the 4.3BSD UNIX Operating System Answer Book, Addison-Wesley, April 1991, ISBN 0-201-54629-9.
Japanese translation published January 1992, ISBN 978-4-8101-8039-8 M. McKusick, K. Bostic, M. Karels, J. Quarterman: The Design and Implementation of the 4.4BSD Operating System, Addison-Wesley, April 1996, ISBN 0-201-54979-4. French translation published 1997, International Thomson Publishing, France, ISBN 2-84180-142-X. McKusick, 1999 Twenty Years of Berkeley Unix M. McKusick, George Neville-Neil: The Design and Implementation of the FreeBSD Operating System, Addison-Wesley, July 2004, ISBN 0-201-70245-2 M. McKusick, G. Neville-Neil, R. Watson: The Design and Implementation of the FreeBSD Operating System, Second Edition, Addison-Wesley, September 2014, ISBN 0-321-96897-2 McKusick's home page