Вольфрам

Описание

Tungsten was recognized as a distinct element in 1779 by Peter Woulfe, but not isolated until 1783, by Jose and Fausto d’Elhuyar. The average tungsten concentration in the earth’s crust is ~0.006%. Tungsten occurs naturally as tungstate, mainly in compounds such as wolframites and scheelites.

Химические свойства

Tungsten is a hard, brittle, steel-gray to tinwhite metal or fine powder.

Физические свойства

Extremely pure samples of tungsten are rather soft and can be cut easily with a simple saw.Pure tungsten can be drawn into fine wires (ductile). On the other hand, if there are even a fewimpurities in the sample, the metal becomes very hard and brittle. It is a very dense metal witha whitish-to-silvery-grayish color when freshly cut. It has the highest melting point of all metalsat 3,422°C, making it a useful metal where high temperatures are required. Incidentally,the transition metals on both sides of it in period 6 (₇₃Ta and ₇₅Re) have the second- and thirdhighestmelting points. Tungsten’s boiling point is also high at 5,927°C.

Изотопы

There are 36 isotopes of tungsten. Five are naturally stable and therefore contributeproportionally to tungsten’s existence on Earth, as follows: W-180 = 0.12%, W-182 = 26.50%, W-183 = 14.31%, W-184 = 30.64%, and W-186 = 28.43%. The other31 isotopes are man-made in nuclear reactors and particle accelerators and have halflivesranging from fractions of a second to many days.

Происхождение имени

Tungsten was originally named “Wolfram” by German scientists, after the mineral in which it was found, Wolframite—thus, its symbol “W.” Later, Swedish scientists named it tung sten, which means “heavy stone,” but it retained its original symbol of “W.”

Вхождение

Tungsten is the 58th most abundant element found on Earth. It is never found in 100%pure form in nature. Its major ore is called wolframite or tungsten tetroxide, (Fe,Mn)WO₄,which is a mixture of iron and manganese and tungsten oxide. During processing, the ore ispulverized and treated with strong alkalis resulting in tungsten trioxide (WO₃), which is thenheated (reduced) with carbon to remove the oxygen. This results in a variety of bright colorchanges and ends up as a rather pure form of tungsten metal: 2WO₃ + 3C → 2WO + 3CO₂.Or, if hydrogen is used as the reducing agent, a more pure form of metal is produced: WO3+ 3H₂ → W + 3H₂O.
Tungsten ores (oxides) are found in Russia, China, South America, Thailand, and Canada.In the United States, the ores are found in Texas, New Mexico, Colorado, California, Arizona,and Nebraska.

Характеристики

Tungsten is considered part of the chromium triad of group six (VIB), which consists of₂₄Cr, ₄₂Mo, and ₇₄W. These elements share many of the same physical and chemical attributes.Tungsten’s high melting point makes it unique insofar as it can be heated to the point thatit glows with a very bright white light without melting. This makes it ideal as a filamentfor incandescent electric light bulbs. Most metals melt long before they reach the point ofincandescence.
Chemically, tungsten is rather inert, but it will form compounds with several other elementsat high temperatures (e.g., the halogens, carbon, boron, silicon, nitrogen, and oxygen).Tungsten will corrode in seawater.

Использование

Tungsten, also known as wolfram, occurs as wolframite (FeWO4). It can be found in the earth’s crust but not in its pure metal form. It combines with other chemicals and compounds within the rocky earth’s crust. It is a transitional hard metal with physicochemical properties and can also be manufactured commercially (Lassner and Schnubert, 1999; Gbaruko and Igwe, 2007; Stefaniak, 2010; Strigul et al., 2010).
Tungsten is most commonly used to increase the hardness of steel. It is available commercially in the form of powder, single crystal, and ultrapure granule grades. It is also used in the manufacturing of alloys, light filaments, and X-ray tubes. A recent use for tungsten is as a lead substitute during the manufacturing of ammunition and sporting good products. Another recent commercial use for tungsten is in the production of wedding bands. It is also used as a catalyst in chemical reactions (Lassner and Schnubert, 1999; Gbaruko and Igwe, 2007; Stefaniak, 2010; Strigul et al., 2010).
To increase hardness, toughness, elasticity, and tensile strength of steel; manufacture of alloys; manufacture of filaments for incandescent lamps and in electron tubes; in contact points for automotive, telegraph, radio and television apparatus; in phonograph needles. Tungsten carbides (W2C, WC) used in rock drills, metal-cutting tools, wire-drawing dies. WC used as catalyst instead of platinum: Bennett et al., Science 184, 563 (1974).

Методы производства

Tungsten occurs principally in the minerals wolframite (Fe,Mn)WO4, scheelite (CaWO4), ferberite (FeWO4), and hubnerite (MnWO4). These ores are found in China, Russia, Canada, Austria, Africa, Bolivia, Columbia, and Portugal. Wolframite is the most important oreworldwide; scheelite is the principal domestic U.S. ore. Scheelite, when pure, contains 80.6% WO3, the most common impurity being MoO3. The percentages of FeO and MnO in wolframite vary considerably; hubnerite is the term applied to ore containing more than 20% MnO and ferberite and to ore containing more than 20% FeO. Intermediate samples are called wolframite.

Определение

tungsten: Symbol W. A white orgrey metallic transition element(formerly called wolfram); a.n. 74;r.a.m. 183.85; r.d. 19.3; m.p. 3410°C;b.p. 5660°C. It is found in a numberof ores, including the oxides wolframite,(Fe,Mn)WO₄, and scheelite,CaWO4. The ore is heated with concentratedsodium hydroxide solutionto form a soluble tungstate. Theoxide WO₃ is precipitated from thisby adding acid, and is reduced to themetal using hydrogen. It is used invarious alloys, especially high-speedsteels (for cutting tools) and in lampfilaments. Tungsten forms a protectiveoxide in air and can be oxidizedat high temperature. It does not dissolvein dilute acids. It forms compoundsin which the oxidation stateranges from +2 to +6. The metal wasfirst isolated by Juan d’Elhuyer andFausto d’Elhuyer (1755–1833) in1783.

Профиль реактивности

Tungsten is stable at room temperature. Very slowly attacked by nitric acid, sulfuric acid, and aqua regia. Dissolved by a mixture of hydrofluoric acid and nitric acid. No reaction with aqueous bases. Attacked rapidly by motlen alkaline melts such as Na2O2 or KNO3/NaOH. Vigorous reactions with bromine trifluoride and chlorine trifluoride. Becomes incandescent upon heating with lead oxide; becomes incandescent in cold fluorine and with iodine pentafluoride. Combustible in the form of finely divided powder and may ignite spontaneously.

Опасность

Tungsten dust, powder, and fine particles will explode, sometimes spontaneously, in air.The dust of many of tungsten’s compounds is toxic if inhaled or ingested.

Угроза здоровью

The soluble compounds of tungsten are distinctly more toxic than the insoluble forms.

Профиль безопасности

An inhalation hazard. Mildly toxic by an unspecified route. An experimental teratogen. Experimental reproductive effects. A skin and eye irritant. Flammable in the form of dust when exposed to flame. The powdered metal may ignite on contact with air or oxidants (e.g., bromine pentafluoride, bromine, chlorine trifluoride, potassium perchlorate, potassium dichromate, nitryl fluoride, fluorine, oxygen difluoride, iodine pentafluoride, hydrogen sulfide, sodlum peroxide, lead (IV)oxide). See also TUNGSTEN COMPOUNDS and POWDERED METALS.

Возможный контакт

Tungsten is used in ferrous and nonferrous alloys, and for filaments in incandescent lamps. It has been stated that the principal health hazards from tungsten and its compounds arise from inhalation of aerosols during mining and milling operations. The principal compounds of tungsten to which workers are exposed are ammonium paratungstate, oxides of tungsten (WO3, W2O5, WO2); metallic tungsten; and tungsten carbide. In the production and use of tungsten carbide tools for machining, exposure to the cobalt used as a binder or cementing substance may be the most important hazard to the health of the employees. Since the cemented tungsten carbide industry uses such other metals as tantalum, titanium, niobium, nickel, chromium, and vanadium in the manufacturing process, the occupational exposures are generally to mixed dust.

Канцерогенность

Tungsten has been suspected to be involved in the occurrence of childhood leukemia, with the discovery of a cluster of diseases in Fallon, Nevada, associated with elevated levels of tungsten in urine and drinking water. The exact environmental source of exposure to tungsten was not clearly identi?ed and there is little evidence for an etiological role of tungsten in eliciting leukemia.

Экологическая судьба

Tungsten in the environment largely exists as ions in compounds and primarily insoluble solids. The potential for particulate matter to spread is low as wet and dry deposition removes it from the atmosphere. If released to air, most tungsten compounds have low vapor pressures and are expected to exist solely in the particulate phase in the ambient atmosphere. Volatization is not expected to be an important fate process.

Перевозки

UN3089 Metal powders, flammable, n.o.s., Hazard Class: 4.1; Labels: 4.1-Flammable solid. UN3189 Metal powder, self heating, n.o.s., Hazard Class: 4.2; Labels: 4.2-Spontaneously combustible material.

Методы очистки

Clean the solid with conc NaOH solution, rub it with very fine emery paper until its surface is bright, wash it with previously boiled and cooled conductivity water and dry it with filter paper. [Hein & Herzog in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol II p 1417 1965.]

Несовместимости

Tungsten: The finely divided powder is combustible and may ignite spontaneously in air. Incompatible with bromine trifluoride; chlorine trifluoride; fluorine, iodine pentafluoride.

Утилизация отходов

Recovery of tungsten from sintered metal carbides, scrap and spent catalysts has been described as an alternative to disposal.