Refractory Hard Metals With a closer look at Tungsten
What are Refractory Hard Metals ?
Refractory metals are a class of metals that are extraordinarily resistant to heat and wear. The expression is mostly used in the context of materials science, metallurgy and engineering. The definition of which elements belong to this group differs. The most common definition includes five elements: niobium, molybdenum, tantalum, tungsten, and rhenium). They all share some properties, including a melting point above 2000 °C and high hardness at room temperature. They are chemically inert and have a relatively high density. Their high melting points make powder metallurgy the method of choice for fabricating components from these metals. Some of their applications include tools to work metals at high temperatures, wire filaments, casting molds, and chemical reaction vessels in corrosive environments. Partly due to the high melting point, refractory metals are stable against creep deformation to very high temperatures.
The wider definition, including all elements with a melting point above 3,362 F(1,850 °C), includes a varying number of nine additional elements: titanium, vanadium, chromium, zirconium, hafnium, ruthenium, rhodium, osmium and iridium.
Carbides
A carbide is a compound composed of carbon and a less electronegative element.
. Examples include calcium carbide (CaC2), silicon carbide (SiC), tungsten carbide (WC) (often called simply carbide when referring to machine tooling Nitrides
a nitride is a compound of nitrogen where nitrogen has a formal oxidation state of −3. Nitrides are a large class of compounds with a wide range of properties and applications.[
Like carbides, nitrides are often refractory materials owing to their high lattice energy which reflects the strong attraction of "N3−" for the metal cation. Thus, titanium nitride and silicon nitride are used as cutting materials and hard coatings. Borides
A boride is a compound between boron and a less electronegative element,
for example silicon boride (SiB3 and SiB6). The borides are a very large group of compounds that are generally high melting and are covalent more than ionic in nature.
The borides can be classified loosely as boron rich or metal rich.
The transition metals tend to form metal rich borides.
Metal-rich borides, as a group, are inert and have high melting temperature.
Silicides
A silicide is a compound that has silicon with (usually) more electropositive elements.
Silicides are structurally closer to borides than to carbides.
Carbides Nitrides Borides Silicides
Metal Carbides Nitrides Borides Silicides
Ti TiC TiN Ti2B Ti2B5 Ti5Si3 TiB TiSi
TiB2 TiSi2
Zr ZrC ZrN ZrB Zr4Si Zr6Si5
ZrB2 Zr2Si ZrSi
ZrB12 Zr3Si2 ZrSi3
Zr4Si3 Carbides Nitrides Borides Silicides
Hf HfC HfN HfB HfB2 V VC V2N VB VN VB2 Nb NbC Nb2N Nb3B Nb3B4 Nb2Si NbN Nb2B NbB2 NbSi2 NbB Ta Ta2C Ta2N Ta3B Ta3B4 Ta5Si Ta5Si3 TaC Ta2B TaB2 Ta5Si2 TaSi2 TaB Carbides Nitrides Borides Silicides
Cr Cr23C6 Cr2N Cr2B Cr3B4 Cr3Si CrSi2 Cr3C2 CrN Cr3B2 CrB2 Cr2Si Cr7C3 CrB CrSi Mo Mo2C Mo2N Mo2B MoB2 Mo3Si MoC MoN Mo3B2 Mo2B5 Mo3Si2 MoB MoSi2 W W2C W2N W2B W2B5 Mo3Si2 WC WB WSi2 History
History
1897 French chemist Moissan published first studies of refractory carbides. Made able by the electric arc furnace he developed.
Refractory metals were of little practical interest until the advent of electricity.
First interest was to replace diamond dies for drawing tungsten filaments Development of Tool Material
Before 1894 Carbon steel Before 1900 Self-hardening steel 1900 First high-speed steel 1906-1913 New high-speed steels 1909 First Stellites 1914 Cast Tungsten Carbide (Cr,Mo,Ta,Co,Fe,C,W) 1917-1923 Tizit Alloys (Cr,Fe,Ti,C,W) 1922 Sintered WC-Co alloys Wida first commercial 1926 1929 Sintered Mo2C-TiC-Ni alloys 1930 Sintered TaC-Ni-Co alloys 1931 Sintered WC-TaC-Co alloys 1931 Sintered WC-TiC-Co alloys 1932 Sintered WC-TaC-TiC-Co alloys
Physical Properties Metal Specific Gravity Melting Point Boiling Point Tungsten (W) 19.3 6170 10,700 Rhenium (Rh) 21.02 5767 10,170 Osmium (Os) 22.59 5491 9054 Tantalum (Ta) 16.69 5463 9856 Molybdenum (Mo) 10.28 4753 8382 Niobium (Nb) 8.57 4491 8571 Iridium (Ir) 22.56 4435 7466 Ruthenium (Ru) 12.45 4233 7502 Hafnium (Ha) 13.31 4051 8317 Rhodium (Ro) 12.41 3567 6683 Vanadium (V) 6 3470 6165 Chromium (Cr) 7.19 3465 4840 Zirconium (Zr) 6.52 3371 7911 Titanium (Ti) 4.506 3034 5949 Niobium (Nb) Niobium, formerly columbium, is a chemical element with symbol Nb(formerly Cb) and atomic number 41. It is a soft, grey, ductile metal, often found in the minerals pyrochlore and columbite. Its name comes from Greek mythology, specifically Niobe, who was the daughter of Tantalus, the namesake of tantalum. The name reflects the great similarity between the two elements in their physical and chemical properties, making them difficult to distinguish. The English chemist Charles Hatchett reported a new element similar to tantalum in 1801 and named it columbium. Niobium was officially adopted as the name of the element in 1949, but the name columbium remains in current use in metallurgy in the United States. It was not until the early 20th century that niobium was first used commercially. Brazil is the leading producer of niobium and ferroniobium, an alloy of niobium and iron which has a niobium content of 60-70%. Niobium is used mostly in alloys, the largest part in special steel such as that used in gas pipelines. Although these alloys contain a maximum of 0.1%, the small percentage of niobium enhances the strength of the steel. The temperature stability of niobium-containing super alloys is important for its use in jet and rocket engines. Niobium is used in various superconducting materials. These superconducting alloys, also containing titanium and tin, are widely used in the superconducting magnets of MRI scanners. Other applications of niobium include welding, nuclear industries, electronics, optics, numismatics, and jewelry. In the last two applications, the low toxicity and iridescence produced by anodization are highly desired properties.
Molybdenum Mo Molybdenum minerals have been known throughout history, but the element was discovered (in the sense of differentiating it as a new entity from the mineral salts of other metals) in 1778 by Carl Wilhelm Scheele. The metal was first isolated in 1781 by Peter Jacob Hjelm. Molybdenum does not occur naturally as a free metal on Earth; it is found only in various oxidation states in minerals. The free element, a silvery metal with a gray cast, has the sixth-highest melting point of any element. It readily forms hard, stable carbides in alloys, and for this reason most of world production of the element (about 80%) is used in steel alloys, including high- strength alloys and super alloys. Most molybdenum compounds have low solubility in water, but when molybdenum- bearing minerals contact oxygen and water, the resulting molybdate ion MoO2−4 is quite soluble. Industrially, molybdenum compounds(about 14% of world production of the element) are used in high-pressure and high-temperature applications as pigments and catalysts. Molybdenum-bearing enzymes are by far the most common bacterial catalysts for breaking the chemical bond in atmospheric molecular nitrogen in the process of biological nitrogen fixation.
Iridium Ir
Iridium Ir a very hard, brittle, silvery-white metal of the platinum group.
Iridium is the second densest element.
It is also the most corrosion-resistant metal, even at temperatures as high as 2000 °C. ,finely divided iridium dust is much more reactive and can be flammable.
Iridium was discovered in 1803 among insoluble impurities in natural platinum. Smithson Tennant, the primary discoverer, named iridium for the Greek goddess Iris, personification of the rainbow, because of the striking and diverse colors of its salts.
Iridium is one of the rarest elements in Earth's crust, with annual production and consumption of only three tons.
The most important iridium compounds in use are the salts and acids it forms with chlorine, though iridium also forms a number of organometallic compounds used in industrial catalysis, and in research.
Iridium metal is employed when high corrosion resistance at high temperatures is needed, as in high- performance spark plugs, crucibles for recrystallization of semiconductors at high temperatures, and electrodes for the production of chlorine in the chloralkaline process.
Iridium radioisotopes are used in some radioisotope thermoelectric generators.
Iridium is found in meteorites in much higher abundance than in the Earth's crust
It is thought that the total amount of iridium in the planet Earth is much higher than that observed in crustal rocks, but as with other platinum-group metals, the high density and tendency of iridium to bond with iron caused most iridium to descend below the crust when the planet was young and still molten.
Osmium Os
Osmium Os is a hard, brittle, bluish-white metal in the platinum group that is found as a trace element in alloys, mostly in platinum ores.
Osmium is the densest naturally occurring element, with a density of 22.59 g/cm3.
Its alloys with platinum, iridium, and other platinum-group metals are employed in fountain pen nib tipping, electrical contacts, and other applications where extreme durability and hardness are needed. Rhodium Rh
Rhodium Rh It is a rare, silvery-white, hard, corrosion resistant and chemically inert metal.
It is a noble metal and a member of the platinum group.
Naturally occurring rhodium is usually found as the free metal, alloyed with similar metals, and rarely as a chemical compound in minerals such as bowieite and rhodplumsite. It is one of the rarest and most valuable precious metals.
Rhodium is found in platinum or nickel ores together with the other members of the platinum group metals.
It was discovered in 1803 by William Hyde Wollaston in one such ore, and named for the rose color of one of its chlorine compounds, produced after it reacted with the powerful acid mixture aqua regia.
The element's major use (approximately 80% of world rhodium production) is as one of the catalysts in the three-way catalytic converters in automobiles.
Because rhodium metal is inert against corrosion and most aggressive chemicals, and because of its rarity, rhodium is usually alloyed with platinum or palladium and applied in high- temperature and corrosion-resistive coatings. White gold is often plated with a thin rhodium layer to improve its appearance while sterling silver is often rhodium-plated for tarnish resistance.
Rhodium detectors are used in nuclear reactors to measure the neutron flux level.
Ruthenium Ru Ruthenium Ru is a rare metal belonging to the platinum group of the periodic table.
Like the other metals of the platinum group, ruthenium is inert to most other chemicals.
The Russian-born scientist of Baltic-German ancestry and a member of the Russian Academy of Science Karl Ernst Claus discovered the element in 1844 at Kazan State University in Russia and named it after the Latin name of his homeland, Rus.
Ruthenium is usually found as a minor component of platinum ores; the annual production is about 20 tonnes.
Most ruthenium produced is used in wear-resistant electrical contacts and thick-film resistors
A minor application for ruthenium is in platinum alloys and as a chemistry catalyst. Hafnium Hf Hafnium Hf A lustrous, silvery gray, metal. Hafnium chemically resembles zirconium and is found in many zirconium minerals. Its existence was predicted by Dmitri Mendeleev in 1869, though it was not identified until 1923, by Coster and Hevesy, making it the last stable element to be discovered. Hafnium is named after Hafnia, the Latin name for Copenhagen, where it was discovered. Hafnium is used in filaments and electrodes. Some semiconductor fabrication processes use its oxide for integrated circuits at 45 nm and smaller feature lengths. Some super alloys used for special applications contain hafnium in combination with niobium, titanium, or tungsten. Hafnium's large neutron capture cross-section makes it a good material for neutron absorption in control rods in nuclear power plants, but at the same time requires that it be removed from the neutron-transparent corrosion-resistant zirconium alloys used in nuclear reactors. Zirconium Zr
Zirconium Zr Zirconium is a lustrous, greyish-white, soft, ductile and malleable metal that is solid at room temperature, though it is hard and brittle at lesser purities.
In powder form, zirconium is highly flammable, but the solid form is much less prone to ignition.
Zirconium is highly resistant to corrosion by alkalis, acids, salt water and other agents. However, it will dissolve in hydrochloric and sulfuric acid. especially when fluorine is present.
Alloys with zinc are magnetic at less than 35 K. the name zirconium is taken from the name of the mineral zircon, the most important source of zirconium. -meaning "goldزرگون, The word zircon comes from the Persian word zargun colored".
It is a lustrous, grey-white, strong metal that resembles hafnium and, to a lesser extent, titanium.
Zirconium is mainly used as a refractory and opacifier
Small amounts are used as an alloying agent for its strong resistance to corrosion.
Zirconium
The principal commercial source of zirconium is zircon (ZrSiO4), a silicate mineral, which is found primarily in Australia, Brazil, India, Russia, South Africa and the United States, as well as in smaller deposits around the world.
The most common oxide is zirconium dioxide, ZrO2, also known as zirconia. This clear to white-coloured solid has exceptional fracture toughness and chemical resistance, especially in its cubic form. These properties make zirconia useful as a thermal barrier coating, although it is also a common diamond substitute Most zircon is used directly in high-temperature applications. This material is refractory, hard, and resistant to chemical attack. Because of these properties, zircon finds many applications, few of which are highly publicized. Its main use is as an opacifier, conferring a white, opaque appearance to ceramic materials. Because of its chemical resistance, zircon is also used in aggressive environments, such as moulds for molten metals.
Zirconium dioxide (ZrO2) is used in laboratory crucibles, in metallurgical furnaces, and as a refractory material.[ Because it is mechanically strong and flexible, it can be sintered into ceramic knives and other blades.
Zircon (ZrSiO4) and the cubic zirconia (ZrO2) are cut into gemstones for use in jewelry. Zirconia is a component in some abrasives, such as grinding wheels and sandpaper.
Zirconium Zirconium tungstate has the unusual property of shrinking in all dimensions when heated, whereas most other substances expand when heated.
A small fraction of the zircon is converted to the metal, which finds various niche applications. Because of zirconium's excellent resistance to corrosion, it is often used as an alloying agent in materials that are exposed to aggressive environments, such as surgical appliances, light filaments, and watch cases.
The high reactivity of zirconium with oxygen at high temperatures is exploited in some specialised applications such as explosive primers and as getters in vacuum tubes.
The same property is (probably) the purpose of including Zr nano-particles as pyrophoric material in explosive weapons such as the BLU-97/B Combined Effects Bomb.
Materials fabricated from zirconium metal and ZrO2 are used in space vehicles where resistance to heat is needed.
High temperature parts such as combustors, blades, and vanes in jet engines and stationary gas turbines are increasingly being protected by thin ceramic layers, usually composed of a mixture of zirconia and yttria
Chromium Cr
Chromium Cr is a steely-grey, lustrous, hard and brittle metal which takes a high polish, resists tarnishing, and has a high melting point. The name of the element is derived from the Greek word χρῶμα, chrōma, meaning color, because many chromium compounds are intensely colored. Ferrochromium alloy is commercially produced from chromite by silicothermic or aluminothermic reactions and chromium metal by roasting and leaching processes followed by reduction with carbon and then aluminum. Chromium metal is of high value for its high corrosion resistance and hardness. A major development was the discovery that steel could be made highly resistant to corrosion and discoloration by adding metallic chromium to form stainless steel. Stainless steel and chrome plating together comprise 85% of the commercial use. Trivalent chromium (Cr(III)) ion is an essential nutrient in trace amounts in humans for insulin, sugar and lipid metabolism. While chromium metal and Cr(III) ions are not considered toxic, hexavalent chromium (Cr(VI)) is toxic and carcinogenic. Abandoned chromium production sites often require environmental cleanup. Titanium Ti
Titanium is a lustrous metal with a silver color, low density, and high strength. Titanium is resistant to corrosion in sea water, aqua regia, and chlorine.
Titanium was discovered by William Gregor in 1791, and was named for the Titans of Greek mythology.
The element occurs within a number of mineral deposits, principally rutile and ilmenite, which are widely distributed in the Earth's crust it is found in almost all living things, water bodies, rocks, and soils.
The metal is extracted from its principal mineral ores by the Kroll[7] and Hunter processes.
The most common compound, titanium dioxide, is a popular photocatalyst and is used in the manufacture of white pigments.
Other compounds include titanium tetrachloride(TiCl4), a component of smoke screens and catalysts; and titanium trichloride (TiCl3), which is used as a catalyst in the production of polypropylene.[6] Titanium
Titanium can be alloyed with iron, aluminum, vanadium, and molybdenum, among other elements, to produce strong, lightweight alloys for aerospace (jet engines, missiles, and spacecraft), military, industrial processes (chemicals and petrochemicals, desalination plants, pulp, and paper), automotive, agri-food, medical prostheses, orthopedic implants, dental and endodontic instruments and files, dental implants, sporting goods, jewelry, mobile phones, and other applications. The two most useful properties of the metal are corrosion resistance and strength-to-density ratio, the highest of any metallic element.[9] In its unalloyed condition, titanium is as strong as some steels, but less dense. Titanium nitride (TiN) has a hardness equivalent to sapphire and carborundum (9.0 on the Mohs Scale), and is often used to coat cutting tools, such as drill bits. It is also used as a gold-colored decorative finish and as a barrier metal in semiconductor fabrication. Titanium carbide, which is also very hard, is found in cutting tools and coatings. Vanadium V Vanadium V is a hard, silvery grey, ductile, and malleable . The elemental metal is rarely found in nature, but once isolated artificially, the formation of an oxide layer stabilizes the free metal somewhat against further oxidation. Andrés Manuel del Río discovered compounds of vanadium in 1801 in Mexico by analyzing a new lead-bearing mineral he called "brown lead", and presumed its qualities were due to the presence of a new element, which he named erythronium (derived from Greek for "red") since, upon heating, most of the salts turned red. Four years later, however, he was (erroneously) convinced by other scientists that erythronium was identical to chromium. Chlorides of vanadium were generated in 1830 by Nils Gabriel Sefström who thereby proved that a new element was involved, which he named "vanadium" after the Scandinavian goddess of beauty and fertility, Vanadís(Freyja). Both names were attributed to the wide range of colors found in vanadium compounds. Del Rio's lead mineral was later renamed vanadinitefor its vanadium content. In 1867 Henry Enfield Roscoe obtained the pure element. Vanadium occurs naturally in about 65 different minerals and in fossil fueldeposits. It is produced in China and Russia from steel smelter slag; other countries produce it either from the flue dust of heavy oil, or as a byproduct of uranium mining. It is mainly used to produce specialty steel alloys such as high-speed tool steels. The most important industrial vanadium compound, vanadium pentoxide, is used as a catalyst for the production of sulfuric acid. Vanadium The first large-scale industrial use of vanadium was in the steel alloy chassis of the Ford Model T, inspired by French race cars. Vanadium steel allowed for reduced weight while simultaneously increasing tensile strength.
Approximately 85% of vanadium produced is used as ferrovanadium or as a steel additive.[37]The considerable increase of strength in steel containing small amounts of vanadium was discovered in the early 20th century.
Vanadium forms stable nitrides and carbides, resulting in a significant increase in the strength of steel. From that time on, vanadium steel was used for applications in axles, bicycle frames, crankshafts, gears, and other critical components.
There are two groups of vanadium steel alloys. Vanadium high-carbon steel alloys contain 0.15% to 0.25% vanadium, and high-speed tool steels (HSS) have a vanadium content of 1% to 5%. For high-speed tool steels, a hardness above HRC 60 can be achieved. HSS steel is used in surgical instruments and tools.
Powder-metallurgic alloys contain up to 18% percent vanadium. The high content of vanadium carbides in those alloys increases wear resistance significantly. One application for those alloys is tools and knives.[41]
Vanadium stabilizes the beta form of titanium and increases the strength and temperature stability of titanium. Mixed with aluminum in titanium alloys, it is used in jet engines, high- speed airframes and dental implants. The most common alloy for seamless tubing is Titanium 3/2.5 containing 2.5% vanadium, the titanium alloy of choice in the aerospace, defense and bicycle industries.[42] Another common alloy, primarily produced in sheets, is Titanium 6AL-4V, a titanium alloy with 6% aluminum and 4% vanadium.[43]
Rhenium Re Rhenium Re is a silvery-white, heavy, metal. With an estimated average concentration of 1 part per billion (ppb), rhenium is one of the rarest elements in the Earth's crust. Rhenium has the third-highest melting point and second-highest boiling point of any element. Rhenium resembles manganese and is mainly obtained as a by-product of the extraction and refinement of molybdenum and copper ores Discovered in 1908, rhenium was the second-last stable element to be discovered. It was named after the river Rhine in Europe. Nickel-based super alloys of rhenium are used in the combustion chambers, turbine blades, and exhaust nozzles of jet engines. These alloys contain up to 6% rhenium, making jet engine construction the largest single use for the element. The second-most important use is as a catalyst: rhenium is an excellent catalyst and is used for example in catalytic reforming of naphtha for use in gasoline. Because of the low availability relative to demand, rhenium is expensive, with an average price of approximately US$2,750 per kilogram(US$85.53 per troy ounce) Tantalum Ta Tantalum Ta its name comes from Tantalus, a villain from Greek mythology. Tantalum was discovered in Sweden in 1802 by Anders Ekeberg.
Tantalum is a rare, hard, blue-gray, lustrous metal that is highly corrosion- resistant.
It is part of the refractory metals group, which are widely used as minor components in alloys.
The chemical inertness of tantalum makes it a valuable substance for laboratory equipment and a substitute for platinum.
Its main use today is in tantalum capacitors in electronic equipment such as mobile phones, DVD players, video game systems and computers.
Tantalum, always together with the chemically similar niobium, occurs in the minerals tantalite, columbite and coltan (a mix of columbite and tantalite). Tantalum All welding of tantalum must be done in an inert atmosphere of argon or helium in order to shield it from contamination with atmospheric gases. Tantalum is not solder able. Grinding tantalum is difficult, especially so for annealed tantalum. In the annealed condition, tantalum is extremely ductile and can be readily formed as metal sheets. The high melting point and oxidation resistance lead to the use of the metal in the production of vacuum furnace parts. Tantalum is extremely inert and is therefore formed into a variety of corrosion resistant parts, such as thermowells, valve bodies, and tantalum fasteners.
Due to its high density, shaped charge and explosively formed penetrator liners have been constructed from tantalum. Tantalum greatly increases the armor penetration capabilities of a shaped charge due to its high density and high melting point Tantalum is also highly bioinert and is used as an orthopedic implant material. The high stiffness of tantalum makes it necessary to use it as highly porous foam or scaffold with lower stiffness for hip replacement implants to avoid stress shielding.[ Because tantalum is a non-ferrous, non-magnetic metal, these implants are considered to be acceptable for patients undergoing MRI procedures. The oxide is used to make special high refractive index glass for camera lenses. Tungsten (W) wolfgram Tungsten W. The name tungsten comes from the former Swedish name for the tungstate mineral scheelite, from tung sten "heavy stone". Tungsten is a rare metal found naturally on Earth almost exclusively in chemical compounds. It was identified as a new element In 1781, Carl Wilhelm Scheele discovered that a new acid, tungstic acid, could be made from scheelite (at the time named 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 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. The name "tungsten" (from the Swedish tung sten, "heavy stone") is used in English, French, and many other languages as the name of the element, but not in the Nordic countries. Tungsten was the old Swedish name for the mineral scheelite. "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.[11] The name "wolframite" is derived from German "wolf rahm" ("wolf soot" or "wolf cream"), the name given to tungsten by Johan Gottschalk Wallerius in 1747. This, in turn, derives from "lupi spuma", the name Georg Agricola used for the element 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.
Tungsten
Tungsten is found mainly in the mineral wolframite (iron–manganese tungstate (Fe,Mn)WO4, which is a solid solution of the two minerals ferberite FeWO4, and hübnerite MnWO4) and scheelite (calcium tungstate (CaWO4). Other tungsten minerals range in their level of abundance from moderate to very rare, and have almost no economical value. In World War II, tungsten played a 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 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. Its density is 19.3 times that of water, comparable to that of uranium and gold, and much higher (about 1.7 times) than that of lead. Tungsten is remarkable for its robustness, especially the fact that it has the highest melting point of all the elements discovered, melting at 3422 °C (6192 °F, 3695 K). It also has the second highest boiling point, at 5930 °C (10706 °F, 6203 K). Although carbon remains solid at higher temperatures than tungsten, carbon sublimes at atmospheric pressure instead of melting, so it has no melting point. Tungsten
Polycrystalline tungsten is an intrinsically brittle and hard material (under standard conditions, when uncombined), making it difficult to work.
However, pure single-crystalline tungsten is more ductile, and can be cut with a hard-steel hacksaw.[11]
Tungsten's many alloys have numerous applications, including incandescent light bulb filaments, X-ray tubes (as both the filament and target), electrodes in TIG welding, superalloys, and radiation shielding.
Tungsten's hardness and high density give it military applications in penetrating projectiles. Tungsten compounds are also often used as industrial catalysts.
Tungsten objects are also commonly formed by sintering. Tungsten
In its raw form, tungsten is a hard steel-grey metal that is often brittle and hard to work. If made very pure, 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.
Of all metals in pure form, tungsten has the highest melting point, lowest vapor pressure (at temperatures above 1650 °C, 3000 °F), and the highest tensile strength.
Tungsten has the lowest coefficient of thermal expansion of any pure metal.
Alloying small quantities of tungsten with steel greatly increases its toughness.[8]
Tungsten carbide (WC) are produced by heating powdered tungsten with carbon.
W2C is made my melting tungsten in the presence of carbon. It resistant to chemical attack.
Tungsten
Approximately half of the tungsten is consumed for the production of hard materials – namely tungsten carbide – with the remaining major use being in alloys and steels.
Less than 10% is used in other chemical compounds
Tungsten heaviest element known to be essential to any living organism.[ Tungsten interferes with molybdenum and copper metabolism and is somewhat toxic to animal life.
Production
2010, world production of tungsten was about 68,000 tonnes.
There is additional production in the U.S., but the amount is proprietary company information.
U.S. reserves are 140,000 tonnes. US industrial use of tungsten is 20,000 tones: 15,000 tones are imported and the remaining 5,000 tones come from domestic recycling.
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. With recent increases in tungsten prices, as of 2014 this mine has been reactivated.
Tungsten is not traded as a futures contract and cannot be tracked on exchanges like the London Metal Exchange. The prices are usually quoted for
tungsten concentrate or WO3. If converted to the metal equivalent, they were about US$19 per kilogram in 2009.
Production (tonnes) Country 2009 2010 2011 2012 Australia 33 18 15 290 China 51,000 59,000 61,800 64,000 Russia 2,665 2,785 3,314 3,537 Canada 1,964 420 1,966 2,194 Bolivia 1,023 1,204 1,124 1,247 Vietnam 725 1,150 1,635 1,050 Portugal 823 799 819 763 Austria 887 977 861 706 Rwanda 380 330 520 700 Spain 225 240 497 542 Brazil 192 166 244 381 Peru 502 571 439 276 Burundi 110 100 165 190 Myanmar 874 163 140 140 North Korea 100 110 110 100 Total 61,200 68,400 73,900 76,400 Tungsten Ores
Scheelite Wolframite
Tungsten is found mainly in the mineral wolframite (iron–manganese tungstate
(Fe,Mn)WO4, which is a solid solution of the two minerals ferberite FeWO4, and hübnerite MnWO4) and scheelite (calcium tungstate (CaWO4). Other tungsten minerals range in their level of abundance from moderate to very rare, and have almost no economical value.
Tungsten is extracted from its ores in several stages.
The last putrefaction stage soluble tungstate is percipated this is were the grain size is determined.
The ore is eventually converted to tungsten(VI) oxide (WO3), which 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. Mining Tungsten in North America
Tungsten Carbide
Tungsten Carbide is made in two basic forms.
WC which is about 6% carbon is made through powder metallurgy and used to make most tungsten carbide.
W2C which is about 3.5% carbon is made by melting tungsten and carbon together. It is often referred simply as cast carbide.
W2C is harder and more brittle and is used mostly in hardfacing products.
WC
WC is mixed with cobalt and sintered to make carbide inserts. Typical cobalt content is 5-20% with the most common being 6 or 12%.
Other carbides like TiC and TaC may be added to give enhanced properties.
Straight WC grades can be used as cutting tools and are the grade that is almost exclusively used in mining and oil field drilling.
WC is believed to be the strongest material in the world with an estimated tensile strength of over 1 million psi.
Strength of WC sintered parts is measured by Transverse Rupture Strength and is In the range of a min. of 250,000 psi to well over 300,000 psi.
Nickel can be used as binder for WC in places where cobalt cannot be used such as nuclear power plants.
Recycling Tungsten
Three ways to recycle tungsten carbide
Brute force
Zinc reclaim
Re-refining
Brute Force
Tungsten carbide though strong is brittle. Parts can be broken by physical means. This is a very maintaince intensive process.
Various crushing equipment is used in the process.
Large parts can be thermal fractured by heating to cherry red and quenching in water. This can be repeated several times until desired reduction is achieved. Jaw crushers can be used for part up to about 1” thick
Hammer mills can be used for smaller parts
As the parts become more “rounded” the crushing becomes more difficult.
More energy is required for reduction.
Each crushing stage results in about a 3:1 reduction.
Impact mills use high velocities for crushing High energy vibratory mills can reduce tungsten to less than 325 mesh. Zinc Reclaim
Zinc reclaim process for the recovery of scrap tungsten carbide.
The process uses molten zinc to break down the cobalt bond structure.
Then the zinc is removed, leaving a friable tungsten carbide residue that is easily crushed for re-use, with ≤50 ppm zinc remaining.
This allows reprocessing like virgin carbide.
Any added carbides, eg Tic or TaC are not removed.
The reprocessed carbide has very little difference from the virgin product.
Re-refining
In the handling of fine powder some material is “lost”. It may end up on the floor, walls, or other equipment.
This material still has value but is contaminated with dust, or a mix of various carbides.
The very fine tungsten carbide material is burned in air to form WO3.
The WO3 is dissolved to form tungstate and refined like virgin tungsten.