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123-525: The WEST , or Tungsten ( chemical symbol " W ") E nvironment in S teady-state T okamak, (formerly Tore Supra ) is a French tokamak that originally began operating as Tore Supra after the discontinuation of TFR (Tokamak of Fontenay-aux-Roses ) and of Petula (in Grenoble ). The original name came from the words torus and superconductor , as Tore Supra was for a long time the only tokamak of this size with superconducting toroidal magnets, allowing

246-425: A body-centered cubic structure and is the more stable form. The structure of the β phase is called A15 cubic ; it is metastable , but can coexist with the α phase at ambient conditions owing to non-equilibrium synthesis or stabilization by impurities. Contrary to the α phase which crystallizes in isometric grains, the β form exhibits a columnar habit . The α phase has one third of the electrical resistivity and

369-474: A liquid crystal -type face plate that self-darkens upon exposure to the bright light of the struck arc. Transparent welding curtains, made of a strongly colored polyvinyl chloride plastic film, are often used to shield nearby workers and bystanders from exposure to the UV light from the electric arc. Welders are also often exposed to dangerous gases and particulate matter. While the process doesn't produce smoke,

492-437: A sextuple bond between tungsten atoms — the highest known bond order among stable atoms. In 1781, Carl Wilhelm Scheele discovered that a new acid , tungstic acid , could be made from scheelite (at the time called tungsten). Scheele and Torbern Bergman suggested that it might be possible to obtain a new metal by reducing this acid. In 1783, José and Fausto Elhuyar found an acid made from wolframite that

615-501: A US court rejected General Electric 's attempt to patent it, overturning U.S. patent 1,082,933 granted in 1913 to William D. Coolidge . It is suggested that remnants of wolfram have been found in what may have been the garden of the astronomer/alchemist Tycho Brahe The name tungsten (which means ' heavy stone ' in Swedish and was the old Swedish name for the mineral scheelite and other minerals of similar density)

738-452: A clean finish or a ground finish—clean finish electrodes have been chemically cleaned, while ground finish electrodes have been ground to a uniform size and have a polished surface, making them optimal for heat conduction. The diameter of the electrode can vary between 0.5 and 6.4 millimetres (0.02 and 0.25 in), and their length can range from 75 to 610 millimetres (3.0 to 24.0 in). A number of tungsten alloys have been standardized by

861-490: A clean weld pool during welding, the shielding gas flow should be sufficient and consistent so that the gas covers the weld and blocks impurities in the atmosphere. GTAW in windy or drafty environments increases the amount of shielding gas necessary to protect the weld, increasing the cost and making the process unpopular outdoors. The level of heat input also affects weld quality. Low heat input, caused by low welding current or high welding speed, can limit penetration and cause

984-568: A colorless gas. At around 250 °C it will react with chlorine or bromine, and under certain hot conditions will react with iodine. Finely divided tungsten is pyrophoric . The most common formal oxidation state of tungsten is +6, but it exhibits all oxidation states from −2 to +6. Tungsten typically combines with oxygen to form the yellow tungstic oxide , WO 3 , which dissolves in aqueous alkaline solutions to form tungstate ions, WO 4 . Tungsten carbides (W 2 C and WC) are produced by heating powdered tungsten with carbon. W 2 C

1107-426: A different atom such as phosphorus in place of the two central hydrogens in metatungstate produces a wide variety of heteropoly acids, such as phosphotungstic acid H 3 PW 12 O 40 . Tungsten trioxide can form intercalation compounds with alkali metals. These are known as bronzes ; an example is sodium tungsten bronze . In gaseous form, tungsten forms the diatomic species W 2 . These molecules feature

1230-403: A filler metal into the weld area with one hand while manipulating the welding torch in the other. Maintaining a short arc length, while preventing contact between the tungsten electrode and the workpiece, is also important. To strike the welding arc, a high-frequency generator (similar to a Tesla coil ) provides an electric spark . This spark is a conductive path for the welding current through

1353-422: A half-life of (1.8 ± 0.2) × 10 years; on average, this yields about two alpha decays of W per gram of natural tungsten per year. This rate is equivalent to a specific activity of roughly 63 micro- becquerel per kilogram. This rate of decay is orders of magnitude lower than that observed in carbon or potassium as found on earth, which likewise contain small amounts of long-lived radioactive isotopes. Bismuth

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1476-632: A high melting point , elemental tungsten is used in many high-temperature applications, such as incandescent light bulb , cathode-ray tube , and vacuum tube filaments, heating elements , and rocket engine nozzles. Its high melting point also makes tungsten suitable for aerospace and high-temperature uses such as electrical, heating, and welding applications, notably in the gas tungsten arc welding process (also called tungsten inert gas (TIG) welding). Gas tungsten arc welding Gas tungsten arc welding ( GTAW , also known as tungsten inert gas welding or TIG , and heliarc welding when helium

1599-447: A joint thickness of less than 1.6 mm (0.063 in). A thoriated tungsten electrode is commonly used, along with pure argon shielding gas. For GTAW of carbon and stainless steels, the selection of filler material is important to prevent excessive porosity. Oxides on the filler material and workpieces must be removed before welding to prevent contamination, and immediately prior to welding, alcohol or acetone should be used to clean

1722-408: A material compatible with particular filler metal, and then welded. In addition, GTAW can be used in cladding or overlaying dissimilar materials. When welding dissimilar metals, the joint must have an accurate fit, with proper gap dimensions and bevel angles. Care should be taken to avoid melting excessive base material. Pulsed current is particularly useful for these applications, as it helps limit

1845-479: A maximum of 150 °C (302 °F) for thick magnesium workpieces to improve penetration and increase travel speed. Alternating current can provide a self-cleaning effect, removing the thin, refractory aluminum oxide layer that forms on aluminum within minutes of exposure to air. This oxide layer must be removed for welding to occur. When alternating current is used, pure tungsten electrodes or zirconiated tungsten electrodes are preferred over thoriated electrodes, as

1968-518: A metal coated in oil to prevent the rod oxidising if needed or in more complicated welding of metals the rod would be coated in a "flux" that was not an active flux but a method of protecting the welding rods from oxidisation during storage (the major examples of this were rods for welding; pure aluminium, duralumin, magnesium/aluminium alloy and stainless steel rods used for repairing ultra high grade carbon steel as in WW2 Sherman tanks). At this time

2091-638: A much lower superconducting transition temperature T C relative to the β phase: ca. 0.015 K vs. 1–4 K; mixing the two phases allows obtaining intermediate T C values. The T C value can also be raised by alloying tungsten with another metal (e.g. 7.9 K for W- Tc ). Such tungsten alloys are sometimes used in low-temperature superconducting circuits. Naturally occurring tungsten consists of four stable isotopes ( W, W, W, and W) and one very long-lived radioisotope, W. Theoretically, all five can decay into isotopes of element 72 ( hafnium ) by alpha emission , but only W has been observed to do so, with

2214-480: A negatively charged electrode (DCEN) allows for high penetration. Argon is commonly used as a shielding gas for DCEN welding of aluminum. Shielding gases with high helium contents are often used for higher penetration in thicker materials. Thoriated electrodes are suitable for use in DCEN welding of aluminum. Direct current with a positively charged electrode (DCEP) is used primarily for shallow welds, especially those with

2337-466: A new cooling system, and all-metal cladding, mainly for experiments on tungsten divertor technology for ITER . The reactor was renamed WEST , for "Tungsten ( chemical symbol " W ") E nvironment in S teady-state T okamak". WEST achieved first plasma in December 2016. Tungsten Tungsten (also called wolfram ) is a chemical element ; it has symbol W and atomic number 74. It

2460-410: A number of other areas. Many industries use GTAW for welding thin workpieces, especially nonferrous metals. It is used extensively in the manufacture of space vehicles and is also frequently employed to weld small-diameter, thin-wall tubing such as that used in the bicycle industry. In addition, GTAW is often used to make root or first-pass welds for piping of various sizes. In maintenance and repair work,

2583-401: A number of variations exist. Among the most popular are the pulsed-current, manual programmed, hot-wire, dabber, and increased penetration GTAW methods. Manual gas tungsten arc welding is a relatively difficult welding method, due to the coordination required by the welder. Similar to torch welding, GTAW normally requires two hands, since most applications require that the welder manually feed

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2706-534: A range of oxidation states. Notable examples include the trigonal prismatic W(CH 3 ) 6 and octahedral W(CO) 6 . The world's reserves of tungsten are 3,200,000 tonnes; they are mostly located in China (1,800,000 t), Canada (290,000 t), Russia (160,000 t), Vietnam (95,000 t) and Bolivia . As of 2017, China, Vietnam and Russia are the leading suppliers with 79,000, 7,200 and 3,100 tonnes, respectively. Canada had ceased production in late 2015 due to

2829-440: A result is often automated. After the discovery of the short pulsed electric arc in 1801 by Humphry Davy and of the continuous electric arc in 1802 by Vasily Petrov , arc welding developed slowly. C. L. Coffin had the idea of welding in an inert gas atmosphere in 1890, but even in the early 20th century, welding non-ferrous materials such as aluminum and magnesium remained difficult because these metals react rapidly with

2952-487: A sharp blow. The hardness and heat resistance of tungsten can contribute to useful alloys . A good example is high-speed steel , which can contain as much as 18% tungsten. Tungsten's high melting point makes tungsten a good material for applications like rocket nozzles , for example in the UGM-27 Polaris submarine-launched ballistic missile . Tungsten alloys are used in a wide range of applications, including

3075-419: A shielding gas source. GTAW welding torches are designed for either automatic or manual operation and are equipped with cooling systems using air or water. The automatic and manual torches are similar in construction, but the manual torch has a handle while the automatic torch normally comes with a mounting rack. The angle between the centerline of the handle and the centerline of the tungsten electrode, known as

3198-488: A shortage of tungsten used in the shell core, caused in part by the Wolfram Crisis , limited their use. Tungsten has also been used in dense inert metal explosives , which use it as dense powder to reduce collateral damage while increasing the lethality of explosives within a small radius. Tungsten(IV) sulfide is a high temperature lubricant and is a component of catalysts for hydrodesulfurization . MoS 2

3321-471: A stainless steel wire brush or chemical process can remove oxides from the surfaces of metals like aluminum. Rust on steels can be removed by first grit blasting the surface and then using a wire brush to remove any embedded grit. These steps are especially important when negative polarity direct current is used, because such a power supply provides no cleaning during the welding process, unlike positive polarity direct current or alternating current. To maintain

3444-441: A torch are made of hard alloys of copper or brass so it can transmit current and heat effectively. The tungsten electrode must be held firmly in the center of the torch with an appropriately sized collet , and ports around the electrode provide a constant flow of shielding gas. Collets are sized according to the diameter of the tungsten electrode they hold. The body of the torch is made of heat-resistant, insulating plastics covering

3567-499: A tungsten bar with gold, which has been observed since the 1980s, or taking an existing gold bar, drilling holes, and replacing the removed gold with tungsten rods. The densities are not exactly the same, and other properties of gold and tungsten differ, but gold-plated tungsten will pass superficial tests. Gold-plated tungsten is available commercially from China (the main source of tungsten), both in jewelry and as bars. Because it retains its strength at high temperatures and has

3690-400: A variety of other-than-flat positions, depending on the skill of the welder and the materials being welded. Aluminum and magnesium are most often welded using alternating current, but the use of direct current is also possible, depending on the properties desired. Before welding, the work area should be cleaned and may be preheated to 175 to 200 °C (347 to 392 °F) for aluminum or to

3813-418: A varying arc length. When used with alternating current, argon shielding results in high weld quality and good appearance. Another common shielding gas, helium, is most often used to increase the weld penetration in a joint, to increase the welding speed, and to weld metals with high heat conductivity, such as copper and aluminum. A significant disadvantage is the difficulty of striking an arc with helium gas, and

WEST (formerly Tore Supra) - Misplaced Pages Continue

3936-412: A weld with pinholes, which is weaker than a typical weld. If the amount of current used exceeds the capability of the electrode, tungsten inclusions in the weld may result. Known as tungsten spitting, this can be identified with radiography and can be prevented by changing the type of electrode or increasing the electrode diameter. In addition, if the electrode is not well protected by the gas shield or

4059-414: Is hypoallergenic , and is harder than gold alloys (though not as hard as tungsten carbide), making it useful for rings that will resist scratching, especially in designs with a brushed finish . Because the density is so similar to that of gold (tungsten is only 0.36% less dense), and its price of the order of one-thousandth, tungsten can also be used in counterfeiting of gold bars , such as by plating

4182-475: Is selective laser melting , which is a form of 3D printing and allows creating complex three-dimensional shapes. Tungsten is mainly used in the production of hard materials based on tungsten carbide (WC), one of the hardest carbides . WC is an efficient electrical conductor , but W 2 C is less so. WC is used to make wear-resistant abrasives , and "carbide" cutting tools such as knives, drills, circular saws , dies , milling and turning tools used by

4305-502: Is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a distinct element in 1781 and first isolated as a metal in 1783. Its important ores include scheelite and wolframite , the latter lending the element its alternative name. The free element is remarkable for its robustness, especially the fact that it has the highest melting point of all known elements, melting at 3,422 °C (6,192 °F; 3,695 K). It also has

4428-523: Is a great deal brighter, subjecting operators to strong ultraviolet light. The welding arc has a different range and strength of UV light wavelengths from sunlight, but the welder is very close to the source and the light intensity is very strong. Potential arc light damage includes accidental flashes to the eye or arc eye and skin damage similar to strong sunburn . Operators wear opaque helmets with dark eye lenses and full head and neck coverage to prevent this exposure to UV light. Modern helmets often feature

4551-471: Is conducted across the arc through a column of highly ionized gas and metal vapors known as a plasma . The process grants the operator greater control over the weld than competing processes such as shielded metal arc welding and gas metal arc welding , allowing stronger, higher-quality welds. However, TIG welding is comparatively more complex and difficult to master, and furthermore, it is significantly slower than most other welding techniques. TAG welding

4674-403: Is gas tungsten arc welding (GTAW). Linde Air Products developed a wide range of air-cooled and water-cooled torches, gas lenses to improve shielding, and other accessories that increased the use of the process. Initially, the electrode overheated quickly and, despite tungsten's high melting temperature , particles of tungsten were transferred to the weld. To address this problem, the polarity of

4797-443: Is heated and fusion occurs. Upon dropping to the background current, the weld area is allowed to cool and solidify. Pulsed-current GTAW has a number of advantages, including lower heat input and consequently a reduction in distortion and warpage in thin workpieces. In addition, it allows for greater control of the weld pool, and can increase weld penetration, welding speed, and quality. A similar method, manual programmed GTAW, allows

4920-476: Is heated with hydrogen or carbon to produce powdered tungsten. Because of tungsten's high melting point, it is not commercially feasible to cast tungsten ingots . Instead, powdered tungsten is mixed with small amounts of powdered nickel or other metals, and sintered . During the sintering process, the nickel diffuses into the tungsten, producing an alloy. Tungsten can also be extracted by hydrogen reduction of WF 6 : or pyrolytic decomposition : Tungsten

5043-484: Is in tungsten carbide , a wear-resistant metal used in metalworking , mining , and construction . About 50% of tungsten is used in tungsten carbide, with the remaining major use being alloys and steels: less than 10% is used other compounds. Tungsten is the only metal in the third transition series that is known to occur in biomolecules , being found in a few species of bacteria and archaea . However, tungsten interferes with molybdenum and copper metabolism and

WEST (formerly Tore Supra) - Misplaced Pages Continue

5166-465: Is more ductile and can be cut with a hard-steel hacksaw . Tungsten occurs in many alloys, which have numerous applications, including incandescent light bulb filaments, X-ray tubes , electrodes in gas tungsten arc welding , superalloys , and radiation shielding . Tungsten's hardness and high density make it suitable for military applications in penetrating projectiles . Tungsten compounds are often used as industrial catalysts . Its largest use

5289-642: Is more commonly used for such applications. Tungsten oxides are used in ceramic glazes and calcium / magnesium tungstates are used widely in fluorescent lighting . Crystal tungstates are used as scintillation detectors in nuclear physics and nuclear medicine . Other salts that contain tungsten are used in the chemical and tanning industries. Tungsten oxide (WO 3 ) is incorporated into selective catalytic reduction (SCR) catalysts found in coal-fired power plants. These catalysts convert nitrogen oxides ( NO x ) to nitrogen (N 2 ) and water (H 2 O) using ammonia (NH 3 ). The tungsten oxide helps with

5412-465: Is most commonly used to weld stainless steel and nonferrous materials, such as aluminum and magnesium, but it can be applied to nearly all metals, with a notable exception being zinc and its alloys. Its applications involving carbon steels are limited not because of process restrictions, but because of the existence of more economical steel welding techniques, such as gas metal arc welding and shielded metal arc welding. Furthermore, GTAW can be performed in

5535-424: Is normally used, and thoriated electrodes, tapered to a sharp point, are recommended. Pure argon is used for thin workpieces, but helium can be introduced as thickness increases. Welding dissimilar metals often introduce new difficulties to GTAW welding, because most materials do not easily fuse to form a strong bond. However, welds of dissimilar materials have numerous applications in manufacturing, repair work, and

5658-498: Is not traded as a futures contract and cannot be tracked on exchanges like the London Metal Exchange . The tungsten industry often uses independent pricing references such as Argus Media or Metal Bulletin as a basis for contracts. The prices are usually quoted for tungsten concentrate or WO 3 . Approximately half of the tungsten is consumed for the production of hard materials – namely tungsten carbide – with

5781-663: Is problematic even in depleted form, or where uranium's additional pyrophoric properties are not desired (for example, in ordinary small arms bullets designed to penetrate body armor). Similarly, tungsten alloys have also been used in shells , grenades , and missiles , to create supersonic shrapnel. Germany used tungsten during World War II to produce shells for anti-tank gun designs using the Gerlich squeeze bore principle to achieve very high muzzle velocity and enhanced armor penetration from comparatively small caliber and light weight field artillery. The weapons were highly effective but

5904-426: Is resistant to chemical attack, although it reacts strongly with chlorine to form tungsten hexachloride (WCl 6 ). In aqueous solution, tungstate gives the heteropoly acids and polyoxometalate anions under neutral and acidic conditions. As tungstate is progressively treated with acid, it first yields the soluble, metastable "paratungstate A" anion , W 7 O 24 , which over time converts to

6027-450: Is somewhat toxic to most forms of animal life. In its raw form, tungsten is a hard steel-grey metal that is often brittle and hard to work . Purified, monocrystalline tungsten retains its hardness (which exceeds that of many steels), and becomes malleable enough that it can be worked easily. It is worked by forging , drawing , or extruding but it is more commonly formed by sintering . Of all metals in pure form, tungsten has

6150-638: Is strictly regulated by the Chinese Government, which fights illegal mining and excessive pollution originating from mining and refining processes. There is a large deposit of tungsten ore on the edge of Dartmoor in the United Kingdom , which was exploited during World War I and World War II as the Hemerdon Mine . Following increases in tungsten prices, this mine was reactivated in 2014, but ceased activities in 2018. Within

6273-544: Is used in English, French, and many other languages as the name of the element, but wolfram (or volfram ) is used in most European (especially Germanic and Slavic) languages and is derived from the mineral wolframite , which is the origin of the chemical symbol W . The name wolframite is derived from German wolf rahm ( ' wolf soot, wolf cream ' ), the name given to tungsten by Johan Gottschalk Wallerius in 1747. This, in turn, derives from Latin lupi spuma ,

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6396-439: Is used in the mechanized welding of light gauge stainless steel, but because hydrogen can cause porosity, its uses are limited. Similarly, nitrogen can sometimes be added to argon to help stabilize the austenite in austenitic stainless steels and increase penetration when welding copper. Due to porosity problems in ferritic steels and limited benefits, however, it is not a popular shielding gas additive. Gas Tungsten Arc Welding

6519-456: Is used) is an arc welding process that uses a non-consumable tungsten electrode to produce the weld . The weld area and electrode are protected from oxidation or other atmospheric contamination by an inert shielding gas ( argon or helium ). A filler metal is normally used, though some welds, known as ' autogenous welds ', or ' fusion welds ' do not require it. A constant-current welding power supply produces electrical energy, which

6642-709: The Carrock mine from the German owned Cumbrian Mining Company and, during World War I , restrict German access elsewhere. In World War II , tungsten played a more significant role in background political dealings. Portugal, as the main European source of the element, was put under pressure from both sides , because of its deposits of wolframite ore at Panasqueira . Tungsten's desirable properties such as resistance to high temperatures, its hardness and density, and its strengthening of alloys made it an important raw material for

6765-599: The EU , the Austrian Felbertal scheelite deposit is one of the few producing tungsten mines. Portugal is one of Europe's main tungsten producers, with 121 kt of contained tungsten in mineral concentrates from 1910 to 2020, accounting for roughly 3.3% of the global production. Tungsten is considered to be a conflict mineral due to the unethical mining practices observed in the Democratic Republic of

6888-684: The International Organization for Standardization and the American Welding Society in ISO 6848 and AWS A5.12, respectively, for use in GTAW electrodes, and are summarized in the adjacent table. Filler metals are also used in nearly all applications of GTAW, the major exception being the welding of thin materials. Filler metals are available with different diameters and are made of a variety of materials. In most cases,

7011-429: The 1950s, as the process continued to gain popularity, some users turned to carbon dioxide as an alternative to the more expensive welding atmospheres consisting of argon and helium , but this proved unacceptable for welding aluminum and magnesium because it reduced weld quality, so it is rarely used with GTAW today. The use of any shielding gas containing an oxygen compound, such as carbon dioxide, quickly contaminates

7134-473: The Congo . South Korea's Sangdong mine , one of the world's largest tungsten mines with 7,890,000 tonnes of high-grade tungsten reportedly buried, was closed in 1994 due to low profitability but has since re-registered mining rights and is scheduled to resume activities in 2024. Tungsten is extracted from its ores in several stages. The ore is eventually converted to tungsten(VI) oxide (WO 3 ), which

7257-451: The TAG name as not specific and has fallen out of favour although the basic revolutionary process remains the same. TIG welding is most commonly used to weld thin sections of stainless steel and non-ferrous metals such as aluminium , magnesium , and copper alloys. A related process, plasma arc welding , uses a slightly different welding torch to create a more focused welding arc and as

7380-417: The aerospace and automotive industries and radiation shielding. Superalloys containing tungsten, such as Hastelloy and Stellite , are used in turbine blades and wear-resistant parts and coatings. Tungsten's heat resistance makes it useful in arc welding applications when combined with another highly-conductive metal such as silver or copper. The silver or copper provides the necessary conductivity and

7503-401: The air, resulting in porous, dross -filled welds. Processes using flux-covered electrodes did not satisfactorily protect the weld area from contamination. To solve the problem, bottled inert gases were used in the beginning of the 1930s. A few years later, a direct current , gas-shielded welding process emerged in the aircraft industry for welding magnesium. In early 1940s Northrop Aircraft

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7626-408: The arc distance and voltage change. This is important because most applications of GTAW are manual or semiautomatic, requiring that an operator hold the torch. Maintaining a suitably steady arc distance is difficult if a constant voltage power source is used instead since it can cause dramatic heat variations and make welding more difficult. The preferred polarity of the GTAW system depends largely on

7749-422: The arms industry, both as a constituent of weapons and equipment and employed in production itself, e.g., in tungsten carbide cutting tools for machining steel. Now tungsten is used in many more applications such as aircraft and motorsport ballast weights, darts, anti-vibration tooling, and sporting equipment. Tungsten is unique amongst the elements in that it has been the subject of patent proceedings. In 1928,

7872-450: The brightness of the arc in GTAW can break down surrounding air to form ozone and nitric oxides. The ozone and nitric oxides react with lung tissue and moisture to create nitric acid and ozone burn. Ozone and nitric oxide levels are moderate, but exposure duration, repeated exposure, and the quality and quantity of fume extraction, and air change in the room must be monitored. Welders who do not work safely can contract emphysema and oedema of

7995-448: The closure of its sole tungsten mine. Meanwhile, Vietnam had significantly increased its output in the 2010s, owing to the major optimization of its domestic refining operations, and overtook Russia and Bolivia. China remains the world's leader not only in production, but also in export and consumption of tungsten products. Tungsten production is gradually increasing outside China because of the rising demand. Meanwhile, its supply by China

8118-633: The creation of a strong permanent toroidal magnetic field . After a major upgrade to install tungsten walls and a divertor, the tokamak was renamed WEST. WEST is situated at the nuclear research center of Cadarache , Bouches-du-Rhône in Provence , one of the sites of the Commissariat à l'Énergie Atomique . Tore Supra operated between 1988 and 2010. Its goal was to create long-duration plasmas. The upgrade to WEST took place between 2013 and 2016. WEST has been operating since 2016. Tore Supra holds

8241-546: The decreased weld quality associated with a varying arc length. Argon-helium mixtures are also frequently utilized in GTAW, since they can increase control of the heat input while maintaining the benefits of using argon. Normally, the mixtures are made with primarily helium (often about 75% or higher) and a balance of argon. These mixtures increase the speed and quality of the AC welding of aluminum, and also make it easier to strike an arc. Another shielding gas mixture, argon- hydrogen ,

8364-404: The density, tungsten is seen as an alternative (albeit more expensive) to lead fishing sinkers . Depleted uranium is also used for these purposes, due to similarly high density. Seventy-five-kg blocks of tungsten were used as "cruise balance mass devices" on the entry vehicle portion of the 2012 Mars Science Laboratory spacecraft. It is an ideal material to use as a dolly for riveting , where

8487-404: The diameter of the electrode, but there are no hard rules. The welder judges the effectiveness of the shielding and increases the nozzle size to increase the area protected by the external gas shield as needed. The nozzle must be heat resistant and thus is normally made of alumina or a ceramic material, but fused quartz , a high purity glass, offers greater visibility. Devices can be inserted into

8610-490: The electric arc from volatilization. This loss does not occur with the GTAW process. Because the resulting welds have the same chemical integrity as the original base metal or match the base metals more closely, GTAW welds are highly resistant to corrosion and cracking over long time periods, making GTAW the welding procedure of choice for critical operations like sealing spent nuclear fuel canisters before burial. Gas tungsten arc welding, because it affords greater control over

8733-417: The electrode advances, but it is always kept inside the gas shield to prevent oxidation of its surface and contamination of the weld. Filler rods composed of metals with a low melting temperature, such as aluminum, require that the operator maintain some distance from the arc while staying inside the gas shield. If held too close to the arc, the filler rod can melt before it makes contact with the weld puddle. As

8856-399: The electrode and the workpiece. In order to initially create the arc, the welding area is flooded with inert gas and a high strike voltage (typically 1 kV per 1 mm) is generated by the welding machine to overcome the electric resistivity of the atmosphere surrounding the welding area. With the arc established, the voltage is lowered and current flows between the work piece and electrode. Despite

8979-550: The electrode to the base material, as in DCEN, electrons go the other direction, causing the electrode to reach very high temperatures. To help it maintain its shape and prevent softening, a larger electrode is often used. As the electrons flow toward the electrode, ionized shielding gas flows back toward the base material, cleaning the weld by removing oxides and other impurities and thereby improving its quality and appearance. Alternating current, commonly used when welding aluminum and magnesium manually or semi-automatically, combines

9102-442: The electrode was changed from positive to negative, but the change made it unsuitable for welding many non-ferrous materials. Finally, the development of alternating current units made it possible to stabilize the arc and produce high quality aluminum and magnesium welds. Developments continued during the following decades. Linde developed water-cooled torches that helped prevent overheating when welding with high currents. During

9225-414: The electrode, the arc, or the welding metal. The gas also transfers heat from the tungsten electrode to the metal, and it helps start and maintain a stable arc. The selection of a shielding gas depends on several factors, including the type of material being welded, joint design, and desired final weld appearance. Argon is the most commonly used shielding gas for GTAW, since it helps prevent defects due to

9348-520: The electrode-negative portion of the cycle. Some power supplies enable operators to use an unbalanced alternating current wave by modifying the exact percentage of time that the current spends in each state of polarity, giving them more control over the amount of heat and cleaning action supplied by the power source. In addition, operators must be wary of rectification , in which the arc fails to reignite as it passes from straight polarity (negative electrode) to reverse polarity (positive electrode). To remedy

9471-488: The element tungsten is not ferromagnetic (but iron is), when it is present in steel in these proportions, it stabilizes the martensite phase, which has greater ferromagnetism than the ferrite (iron) phase due to its greater resistance to magnetic domain wall motion . Tungsten, usually alloyed with nickel , iron , or cobalt to form heavy alloys, is used in kinetic energy penetrators as an alternative to depleted uranium , in applications where uranium's radioactivity

9594-473: The filler metal in the form of a rod is added to the weld pool manually, but some applications call for an automatically fed filler metal, which often is stored on spools or coils. As with other welding processes such as gas metal arc welding, shielding gases are necessary in GTAW to protect the welding area from atmospheric gases such as nitrogen and oxygen , which can cause fusion defects, porosity, and weld metal embrittlement if they come in contact with

9717-441: The head angle, can be varied on some manual torches according to the preference of the operator. Air cooling systems are most often used for low-current operations (up to about 200  A ), while water cooling is required for high-current welding (up to about 600 A). The torches are connected with cables to the power supply and with hoses to the shielding gas source and where used, the water supply. The internal metal parts of

9840-402: The heat input. The filler metal should be added quickly, and a large weld pool should be avoided to prevent dilution of the base materials. In the pulsed-current mode, the welding current rapidly alternates between two levels. The higher current state is known as the pulse current, while the lower current level is called the background current. During the period of pulse current, the weld area

9963-496: The high temperatures of this electric arc, the main heat transfer mechanism in GTAW is the joule heating resulting from this current flow. Welders wear protective clothing , including light and thin leather gloves and protective long sleeve shirts with high collars, to avoid exposure to strong ultraviolet light . Due to the absence of smoke in GTAW, the electric arc light is not covered by fumes and particulate matter as in stick welding or shielded metal arc welding , and thus

10086-500: The high wear resistance and thermal conductivity of tungsten carbide improves the printing of abrasive filaments. Some string instrument strings incorporates tungsten. Tungsten is used as an absorber on the electron telescope on the Cosmic Ray System of the two Voyager spacecraft . Its density, similar to that of gold, allows tungsten to be used in jewelry as an alternative to gold or platinum . Metallic tungsten

10209-423: The highest boiling point , at 5,930 °C (10,706 °F; 6,203 K). Its density is 19.254 g/cm , comparable with that of uranium and gold , and much higher (about 1.7 times) than that of lead . Polycrystalline tungsten is an intrinsically brittle and hard material (under standard conditions, when uncombined), making it difficult to work into metal . However, pure single-crystalline tungsten

10332-515: The highest melting point (3,422 °C, 6,192 °F), lowest vapor pressure (at temperatures above 1,650 °C, 3,000 °F), and the highest tensile strength . Although carbon remains solid at higher temperatures than tungsten, carbon sublimes at atmospheric pressure instead of melting, so it has no melting point. Moreover, tungsten's most stable crystal phase does not exhibit any high-pressure-induced structural transformations for pressures up to at least 364 gigapascals. Tungsten has

10455-441: The latter are more likely to "spit" electrode particles across the welding arc into the weld. Blunt electrode tips are preferred, and pure argon shielding gas should be employed for thin workpieces. Introducing helium allows for greater penetration in thicker workpieces, but can make arc starting difficult. Direct current of either polarity, positive or negative, can be used to weld aluminum and magnesium as well. Direct current with

10578-480: The less soluble "paratungstate B" anion, H 2 W 12 O 42 . Further acidification produces the very soluble metatungstate anion, H 2 W 12 O 40 , after which equilibrium is reached. The metatungstate ion exists as a symmetric cluster of twelve tungsten- oxygen octahedra known as the Keggin anion. Many other polyoxometalate anions exist as metastable species. The inclusion of

10701-402: The lowest coefficient of thermal expansion of any pure metal. The low thermal expansion and high melting point and tensile strength of tungsten originate from strong covalent bonds formed between tungsten atoms by the 5d electrons. Alloying small quantities of tungsten with steel greatly increases its toughness . Tungsten exists in two major crystalline forms: α and β. The former has

10824-408: The lungs, which can lead to early death. Similarly, the heat from the arc can cause poisonous fumes to form from cleaning and degreasing materials. Cleaning operations using these agents should not be performed near the site of welding, and proper ventilation is necessary to protect the welder. While the aerospace industry is one of the primary users of gas tungsten arc welding, the process is used in

10947-540: The mass necessary for good results can be achieved in a compact bar. High-density alloys of tungsten with nickel, copper or iron are used in high-quality darts (to allow for a smaller diameter and thus tighter groupings) or for artificial flies (tungsten beads allow the fly to sink rapidly). Tungsten is also used as a heavy bolt to lower the rate of fire of the SWD M11/9 sub-machine gun from 1300 RPM to 700 RPM. Tungsten has seen use recently in nozzles for 3D printing ;

11070-403: The metal components, providing insulation from heat and electricity to protect the welder. The size of the welding torch nozzle depends on the amount of shielded area desired. The size of the gas nozzle depends upon the diameter of the electrode, the joint configuration, and the availability of access to the joint by the welder. The inside diameter of the nozzle is preferably at least three times

11193-431: The metal matrix in place of cobalt because it takes a higher luster when polished. Sometimes manufacturers or retailers refer to tungsten carbide as a metal, but it is a ceramic . Because of tungsten carbide's hardness, rings made of this material are extremely abrasion resistant, and will hold a burnished finish longer than rings made of metallic tungsten. Tungsten carbide rings are brittle, however, and may crack under

11316-538: The metalworking, woodworking, mining , petroleum and construction industries. Carbide tooling is actually a ceramic/metal composite, where metallic cobalt acts as a binding (matrix) material to hold the WC particles in place. This type of industrial use accounts for about 60% of current tungsten consumption. The jewelry industry makes rings of sintered tungsten carbide , tungsten carbide/metal composites, and also metallic tungsten. WC/metal composite rings use nickel as

11439-484: The most prevalent use of TAG welding is in the production of higher end aluminium alloy bicycles, these welds are clearly visible as ripples in the welded joint. Other than mostly bicycle production TAG has been surpassed by the use of tungsten alloy tips and argon gas combined with other inert gasses. TAG welding rods are now highly specific project metal alloy rods or more frequently mass production flexible "flux" cable/wire fed drum machines. These developments have rendered

11562-483: The most stable being W ( t 1/2  6.4 minutes). Tungsten is a mostly non-reactive element: it does not react with water, is immune to attack by most acids and bases, and does not react with oxygen or air at room temperature. At elevated temperatures (i.e., when red-hot) it reacts with oxygen to form the trioxide compound tungsten(VI), WO 3 . It will, however, react directly with fluorine (F 2 ) at room temperature to form tungsten(VI) fluoride (WF 6 ),

11685-412: The most stable of which are W with a half-life of 121.2 days, W with a half-life of 75.1 days, W with a half-life of 69.4 days, W with a half-life of 21.6 days, and W with a half-life of 23.72 h. All of the remaining radioactive isotopes have half-lives of less than 3 hours, and most of these have half-lives below 8 minutes. Tungsten also has 11  meta states , with

11808-721: The name Georg Agricola used for the mineral in 1546, which translates into English as ' wolf's froth ' and is a reference to the large amounts of tin consumed by the mineral during its extraction, as though the mineral devoured it like a wolf. This naming follows a tradition of colorful names miners from the Ore Mountains would give various minerals, out of a superstition that certain ones that looked as if they contained then-known valuable metals but when extracted were somehow "hexed". Cobalt (cf. Kobold ), pitchblende (cf. German blenden for ' to blind, to deceive ' ) and nickel (cf. "Old Nick") derive their names from

11931-437: The nozzle for special applications, such as gas lenses or valves to improve the control shielding gas flow to reduce turbulence and the introduction of contaminated atmosphere into the shielded area. Hand switches to control welding current can be added to the manual GTAW torches. Gas tungsten arc welding uses a constant current power source, meaning that the current (and thus the heat flux ) remains relatively constant, even if

12054-428: The operator accidentally allows it to contact the molten metal, it can become dirty or contaminated. This often causes the welding arc to become unstable, requiring that the electrode be ground with a diamond abrasive to remove the impurity. The equipment required for the gas tungsten arc welding operation includes a welding torch utilizing a non-consumable tungsten electrode, a constant-current welding power supply, and

12177-432: The operator to program a specific rate and magnitude of current variations, making it useful for specialized applications. The dabber variation is used to precisely place weld metal on thin edges. The automatic process replicates the motions of manual welding by feeding a cold or hot filler wire into the weld area and dabbing (or oscillating) it into the welding arc. It can be used in conjunction with pulsed current, and

12300-426: The pervasiveness of the chromium(III) compounds. The highest oxidation state is seen in tungsten(VI) oxide (WO 3 ). Tungsten(VI) oxide is soluble in aqueous base , forming tungstate (WO 4 ). This oxyanion condenses at lower pH values, forming polyoxotungstates . The broad range of oxidation states of tungsten is reflected in its various chlorides: Organotungsten compounds are numerous and also span

12423-619: The physical strength of the catalyst and extends catalyst life. Tungsten containing catalysts are promising for epoxidation, oxidation, and hydrogenolysis reactions. Tungsten heteropoly acids are key component of multifunctional catalysts. Tungstates can be used as photocatalyst, while the tungsten sulfide as electrocatalyst. Applications requiring its high density include weights, counterweights , ballast keels for yachts, tail ballast for commercial aircraft, rotor weights for civil and military helicopters, and as ballast in race cars for NASCAR and Formula One . Being slightly less than twice

12546-455: The prevention of corrosion and oxidation . In some joints, a compatible filler metal is chosen to help form the bond, and this filler metal can be the same as one of the base materials (for example, using a stainless steel filler metal with stainless steel and carbon steel as base materials), or a different metal (such as the use of a nickel filler metal for joining steel and cast iron ). Very different materials may be coated or "buttered" with

12669-416: The problem, a square wave power supply can be used, as can high-frequency to encourage arc stability. The electrode used in GTAW is made of tungsten or a tungsten alloy, because tungsten has the highest melting temperature among pure metals, at 3,422 °C (6,192 °F). As a result, the electrode is not consumed during welding, though some erosion (called burn-off) can occur. Electrodes can have either

12792-491: The process is commonly used to repair tools and dies, especially components made of aluminum and magnesium. Because the weld metal is not transferred directly across the electric arc like most open arc welding processes, a vast assortment of welding filler metal is available to the welding engineer. In fact, no other welding process permits the welding of so many alloys in so many product configurations. Filler metal alloys, such as elemental aluminum and chromium, can be lost through

12915-524: The record of the longest plasma duration time for a tokamak (6 minutes 30 seconds and over 1000 MJ of energy injected and extracted in 2003), and it allowed researchers to test critical parts of equipment such as plasma facing wall components or superconducting magnets that will be used in its successor, ITER . Tore Supra as of 1988: Tore Supra as of 2006 (parameters essentially the same): WEST as of 2018: By 1998 it had produced over 20,000 plasma shots of up to 2 minutes duration. Between 2000 and 2002

13038-402: The remaining major use being in alloys and steels. Less than 10% is used in other chemical compounds . Because of the high ductile-brittle transition temperature of tungsten, its products are conventionally manufactured through powder metallurgy , spark plasma sintering , chemical vapor deposition , hot isostatic pressing , and thermoplastic routes. A more flexible manufacturing alternative

13161-1044: The same miners' idiom. Tungsten has thus far not been found in nature in its pure form. Instead, tungsten is found mainly in the minerals wolframite and scheelite . Wolframite is iron – manganese tungstate (Fe,Mn)WO 4 , a solid solution of the two minerals ferberite (FeWO 4 ) and hübnerite (MnWO 4 ), while scheelite is calcium tungstate (CaWO 4 ). Other tungsten minerals range in their level of abundance from moderate to very rare, and have almost no economic value. Tungsten forms chemical compounds in oxidation states from -II to VI. Higher oxidation states, always as oxides, are relevant to its terrestrial occurrence and its biological roles, mid-level oxidation states are often associated with metal clusters , and very low oxidation states are typically associated with CO complexes . The chemistries of tungsten and molybdenum show strong similarities to each other, as well as contrasts with their lighter congener, chromium . The relative rarity of tungsten(III), for example, contrasts with

13284-409: The shielding gas and allows the arc to be initiated while the electrode and the workpiece are separated, typically about 1.5–3 mm (0.06–0.12 in) apart. Once the arc is struck, the welder moves the torch in a small circle to create a welding pool, the size of which depends on the size of the electrode and the amount of current. While maintaining a constant separation between the electrode and

13407-400: The shielding gas and increasing the temperature of the base material. The ionized shielding gas flows toward the electrode, not the base material, and this can allow oxides to build on the surface of the weld. Direct current with a positively charged electrode (DCEP) is less common, and is used primarily for shallow welds since less heat is generated in the base material. Instead of flowing from

13530-459: The surface. Preheating is generally not necessary for mild steels less than one inch thick, but low alloy steels may require preheating to slow the cooling process and prevent the formation of martensite in the heat-affected zone . Tool steels should also be preheated to prevent cracking in the heat-affected zone. Austenitic stainless steels do not require preheating, but martensitic and ferritic chromium stainless steels do. A DCEN power source

13653-441: The tungsten allows the welding rod to withstand the high temperatures of the arc welding environment. Quenched (martensitic) tungsten steel (approx. 5.5% to 7.0% W with 0.5% to 0.7% C) was used for making hard permanent magnets, due to its high remanence and coercivity , as noted by John Hopkinson (1849–1898) as early as 1886. The magnetic properties of a metal or an alloy are very sensitive to microstructure. For example, while

13776-466: The tungsten electrode, making it unsuitable for the TIG process. In 1953, a new process based on GTAW was developed, called plasma arc welding. It affords greater control and improves weld quality by using a nozzle to focus the electric arc, but is largely limited to automated systems, whereas GTAW remains primarily a manual, hand-held method. Development within the GTAW process has continued as well, and today

13899-409: The two direct currents by making the electrode and base material alternate between positive and negative charge. This causes the electron flow to switch directions constantly, preventing the tungsten electrode from overheating while maintaining the heat in the base material. Surface oxides are still removed during the electrode-positive portion of the cycle and the base metal is heated more deeply during

14022-405: The type of metal being welded. Direct current with a negatively charged electrode (DCEN) is often employed when welding steels , nickel , titanium , and other metals. It can also be used in automatic GTAW of aluminum or magnesium when helium is used as a shielding gas. The negatively charged electrode generates heat by emitting electrons, which travel across the arc, causing thermal ionization of

14145-509: The vacuum chamber was completely renewed/relined. increasing the power extraction by active cooling to 25 MW (to allow longer plasma duration). In December 2003, it achieved a record 6.5 minute plasma This was plasma shot #32299, Lower hybrid power ~2.9 MW, total injected energy ~1.1 GJ, plasma current ~500 kA, nl ~ 2.6x10 m. Beginning in March 2013 Tore Supra underwent an extensive refit, including new poloidal coils to achieve diverted operation,

14268-434: The weld area than other welding processes, can produce high-quality welds when performed by skilled operators. Maximum weld quality is assured by maintaining cleanliness—all equipment and materials used must be free from oil, moisture, dirt and other impurities, as these cause weld porosity and consequently a decrease in weld strength and quality. To remove oil and grease, alcohol or similar commercial solvents may be used, while

14391-406: The weld bead to lift away from the surface being welded. If there is too much heat input, however, the weld bead grows in width while the likelihood of excessive penetration and spatter (emission of small, unwanted droplets of molten metal) increases. Additionally, if the welding torch is too far from the workpiece the shielding gas becomes ineffective, causing porosity within the weld. This results in

14514-422: The weld nears completion, the arc current is often gradually reduced to allow the weld crater to solidify and prevent the formation of crater cracks at the end of the weld. The physics of GTAW involves several complex processes, including thermodynamics, plasma physics, and fluid dynamics. The non-consumable tungsten electrode can be operated as a Cathode or Anode and is used to produce an electric arc between

14637-403: The workpiece, the operator then moves the torch back slightly and tilts it backward about 10–15 degrees from vertical. Filler metal is added manually to the front end of the weld pool as it is needed. Welders often develop a technique of rapidly alternating between moving the torch forward (to advance the weld pool) and adding filler metal. The filler rod is withdrawn from the weld pool each time

14760-569: Was developing an experimental aircraft from magnesium designated XP-56 , for which Vladimir Pavlecka , Tom Piper and Russell Meredith developed a welding process named Heliarc because it used a tungsten electrode arc and helium as a shielding gas (the torch design was patented by Meredith in 1941). It is now often referred to as tungsten inert gas welding (TIG), especially in Europe, but the American Welding Society's official term

14883-490: Was identical to tungstic acid. Later that year, at the Royal Basque Society in the town of Bergara , Spain, the brothers succeeded in isolating tungsten by reduction of this acid with charcoal , and they are credited with the discovery of the element (they called it "wolfram" or "volfram"). The strategic value of tungsten came to notice in the early 20th century. British authorities acted in 1912 to free

15006-585: Was long thought to be non-radioactive, but Bi (its longest lived isotope) actually decays with a half life of 2.01 × 10 years or about a factor 10 slower than W . However, due to naturally occurring bismuth being 100% Bi , its specific activity is actually higher than that of natural tungsten at 3 milli-becquerel per kilogram. The other naturally occurring isotopes of tungsten have not been observed to decay, constraining their half-lives to be at least 4 × 10  years . Another 34 artificial radioisotopes of tungsten have been characterized,

15129-458: Was the name given in the early 1970's to the then novel and revolutionary method of rod welding previously problematic metals. TAG welding was then the use of a tungsten tipped arc creating welding machine. The tip was centred in shroud that fed argon gas around tungsten tip to prevent the composition of the weld becoming oxidised and fragile. TAG welding used rods of a metal suitable for the material to be welded permanently together. The rods could be

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