Молибден химические свойства, назначение, производство
Описание
Molybdenum is an essential trace mineral associated with several enzyme systems required for the normal body functions. Mine workers have developed symptoms of molybdenosis. The significantly expanding or softening property of the material makes it useful in applications that involve intense heat, including the manufacture of aircraft parts, electrical contacts, industrial motors, and filaments.
Химические свойства
Molybdenum is a silvery-white metal or dark
gray or black powder with a metallic luster.
Физические свойства
Molybdenum is in the middle of the triad elements of group 6. These three metals (fromperiods 4, 5, and 6) are chromium, molybdenum, and tungsten, which, in their pure states,are relatively hard, but not as hard as iron. They are silvery-white as pure metals, and they havesimilar oxidation states. Their electronegativity is also similar—Cr = 1.6, Mo = 1.8, and W =1.7—which is related to their reactivity with nonmetals.
Molybdenum is malleable and ductile, but because of its relatively high melting point, it isusually formed into shapes by using powder metallurgy and sintering techniques.
Molybdenum’s melting point is 2,617°C, boiling point = 4,612°C, and its density is 10.22g/cm3.
Изотопы
There are 36 isotopes of molybdenum, ranging in atomic weights from Mo-83to Mo-115. Of the seven isotopes considered stable, one (Mo-100) is radioactive and isconsidered stable because it has such a long half-life (0.95×10+19 years). The proportionsof the seven stable isotopes contributing to molybdenum’s natural existence onEarth are as follows: Mo-92 = 14.84%, Mo-94 = 9.25%, Mo-95 = 15.92%, Mo-96 =16.68%, Mo-97 = 9.55%, Mo-98 = 24.13%, and Mo-100 = 9.63%.
Происхождение имени
Molybdenum is derived from the Greek word molybdos, meaning lead.
At one time, the mineral molybdaena (later called molybdenite) was believed to be a
variety of lead ore.
Вхождение
Molybdenum is the 54th most abundant element on Earth. It is relatively rare and is foundin just 126 ppm in the Earth’s crust. Its major ore is molybdenite (MoS2), which is mined inColorado in the United States and is found too in Canada, Chile, China, England, Norway,Sweden, Mexico, and Australia. Moldybdenum is also found in two less important ores: wulfenite(PbMoO4) and powellite ([Ca(MoW)O4]. These ores are usually found in the same sitesalong with tin and tungsten ores.
Molybdenite ore is very similar to graphite, and they have been mistaken for each otherin the past.
Характеристики
Given that molybdenum is located between chromium and tungsten in group 6, it chemicallyresembles a cross between these two partner elements. The three related elements donot occur as free elements in nature, but rather are found in minerals and ores. Their metal(elemental) radius size increases from chromium = 44 to molybdenum = 59 to tungsten = 60,which is related to their electronegativity and results in their using electrons in shells inside theouter shell during metallic bonding. This is a major characteristic of the transition of elementsfrom metals to nonmetals.
Molybdenum oxidizes at high temperatures but not at room temperatures. It is insolublein acids and hydroxides at room temperatures. At room temperatures, all three metals(chromium, molybdenum, and tungsten) resist atmospheric corrosion, which is one reasonchromium is used to plate other metals. They also resist attacks from acids and strong alkalis,with the exception of chromium, which, unless in very pure form, will dissolve in hydrochloricacid (HCl).
История
Peter Jacob Hjelm (1746–1813) is given credit for discovering molybdenum in 1781despite the fact that his paper was not published until 1890. He followed the advice of CarlWilhelm Scheele (1742–1786), who isolated and identified molybdenum, but incorrectlythought it was an element related to lead.
Although some reference works do give Scheele credit, most do not credit him for thediscovery of either molybdenum or the other elements he “discovered,” such as oxygen andmanganese.
Scheele did not receive credit for discovering oxygen two years before Joseph Priestley(1733–1804) announced his discovery and was given the credit. Scheele’s publisher wasnegligent in getting his work published in time. (There is a lesson in this story for all youngscientists—keep completed and accurate records of all your lab work and observations, andwhen you are sure of your experimental results, make sure to publish.)
The name “molybdenum” is derived from the Greek word for lead, molybdos, which standsfor any black minerals that historically could be used for writing. This also explains why theGreek word plumbago or “black lead” was used for graphite.
Использование
In the form of ferromolybdenum for manufg special steels for tools, boiler plate, rifle barrels, propeller shafts; electrical contacts, spark plugs, x-ray tubes, filaments, screens and grids for radio tubes; in the production of tungsten; glass-to-metal seals; nonferrous alloys; in colloidal form as lubricant additive.
Методы производства
Molybdenum (Mo) is a dark gray or a black powder with a metallic luster and a chemical element of the second transition series. The name is derived from the Greek molybdos, meaning“lead.”In1778,CarlScheeleofSwedenrecognized molybdenite as a distinct ore of a new element, and in 1781 Hjelm prepared an impure form of the metal. The ?rst molybdenum mine, Knaben Gruver mine in southern Norway, was opened in 1885 and remained open until 1973. Today, the principal molybdenum mines are found in the United States, Chile, and China. Mined ore is crushed in ball or rod mills, and metallic minerals are separated from gangue by ?otation. The pure metal is prepared by the reduction of puri?ed molybdic trioxide or ammonium molybdate (AM) with hydrogen. When Mo is a by-product of copper mining, a concentrate ofcopperandmolybdenumis?rstproduced,andthetwoores are later separated by differential ?otation. MoS2 concentrates contain more than 85% MoS2 and roasted MoO3 typically contains a minimum of 57% Mo and less than 0.1% S.
Определение
A transition element that occurs naturally in molybdenite (MoS2) and wulfenite (PbMoO4). It is used in alloy steels, lamp bulbs, and catalysts. The compound ammonium molybdate, dissolved in nitric acid, is used as a test for phosphates(V). Molybdenum sulfide (MoS2) is used in lubricants to enhance viscosity. Symbol: Mo; m.p. 2620°C; b.p. 4610°C; r.d. 10.22 (20°C); p.n. 42; r.a.m. 95.94.
Общее описание
Molybdenum, a chemical element, is a hard, high-melting (refractory) high-density dark gray metal or black powder. Insoluble in water. Used to make structural alloys; used as a catalyst. Molybdenum dust and fumes can irritate the eyes and respiratory tract.
Профиль реактивности
Molybdenum is a reducing agent. In dust or powder form, Molybdenum may present a fire or explosion hazard under favoring conditions of particle size, dispersion and ignition. Bulk Molybdenum (rod, coil, sheet, etc.) is less reactive than dust or powder. Insoluble in hydrochloric acid or hydrofluoric acid solutions and in ammonia and sodium hydroxide solutions. Insoluble in dilute sulfuric acid solutions but soluble in concentrated sulfuric acid. Soluble in concentrated nitric acid. Incompatible with strong oxidizing agents such as bromine trifluoride, bromine pentafluoride, chlorine trifluoride, potassium perchlorate, nitryl fluoride, fluorine, iodine pentafluoride, sodium peroxide, lead dioxide.
Опасность
The powder and dust forms of molybdenum are flammable. The fumes from some of thecompounds should not be inhaled or ingested.
Промышленное использование
Molybdenum (Mo) is a silvery-white metal, occurring chiefly in the mineral molybdenite but also obtained as a by-product from copper ores. It is ductile, softer than tungsten, and is readily worked or drawn into very fine wire.
Its major use is in alloy steels, for example, as tool steels ( 10% molybdenum), stainless steel, and armor plate. Up to 3% molybdenum is added to cast iron to increase strength. Up to 30% molybdenum may be added to iron-, cobalt-, and nickel-base alloys designed for severe heat- and corrosion-resistant applications. It may be used in filaments for lightbulbs, and it has many applications in electronic circuitry.
Molybdenum forms mirrors and films on glass when it is produced by gas-phase reduction or decomposition of volatile molybdenum compounds in glass tubes. Molybdenum trioxide (MoO3) dissolves in glass, allowing strong binding of molten glass with preoxidized metal surfaces. Annealing is very effective, with little or no difference in thermal expansion at the metal glass interface. Molybdenum found early use in filaments for electric lightbulbs and later in the construction of electronic devices (for example, in vacuum tubes, contacts, electrodes, and transistors).
Профиль безопасности
Poison by intratracheal
route. Mutation data reported. An
experimental teratogen. Experimental
reproductive effects. Flammable or
explosive in the form of dust when exposed
to heat or flame. Violent reaction with oxidants (e.g., bromine trifluoride, bromine
pentafluoride. chlorine trifluoride, potassium
perchlorate, nitryl fluoride, fluorine, iodine
pentafluoride, sodium peroxide, lead
dioxide). When heated to decomposition it
emits toxic fumes of Mo.
Возможный контакт
Most of the molybdenum produced is
used in alloys: steel, stainless steel; tool steel; case iron;
steel mill rolls; manganese, nickel, chromium, and tungsten.
The metal is used in electronic parts (contacts, spark
plugs, X-ray tubes, filaments, screens, and grids for radios);
induction heating elements; electrodes for glass melting;
and metal spraying applications. Molybdenum compounds
are utilized as lubricants; as pigments for printing inks; lacquers,
paints, for coloring rubber animal fibers, leather, and
as a mordant; as catalysts for hydrogenation cracking;
alkylation, and reforming in the petroleum industry; in
Fischer Tropsch synthesis; in ammonia production; and in
various oxidation-reduction and organic cracking reactions;
as a coating for quartz glass; in vitreous enamels to increase adherence to steel; in fertilizers, particularly for
legumes; in electroplating to form protective coatings; and
in the production of tungsten. Hazardous exposures may
occur during high-temperature treatment in the fabrication
and production of molybdenum products, spraying applications;
or through loss of catalyst. MoO3 sublimes above
800℃.
Канцерогенность
Guinea pigs exposed to molybdenum trioxide
dust at a concentration of 200mg molybdenum/
m3 for 1 hour daily for 5 days developed
nasal irritation, diarrhea, weight loss, and incoordination.
3 In 2-year inhalation studies at concentrations
of up to 100mg/m3 molybdenum
trioxide there was no evidence of carcinogenic
activity in female rats, but there was equivocal
evidence in males based on a marginally significant
positive trend of alveolar/bronchiolar
adenoma or carcinoma (combined). There was
some evidence of carcinogenic activity in mice
based on increased incidences of alveolar/bronchiolar
adenoma and carcinomas (combined).4
Other exposure-related effects in exposed
animals included alveolar inflammation, squamous
metaplasia of the epiglottis and hyaline
degeneration of the respiratory and olfactory
epithelium. Molybdenum trioxide was not
mutagenic in bacterial assays, nor did it induce
sister chromatid exchanges or chromosomal
aberrations in vitro.
Перевозки
UN3089 Metal powders, flammable, n.o.s.,
Hazard Class: 4.1; Labels: 4.1-Flammable solid.
Несовместимости
Metallic Mo is a combustible solid in
form of dust or powder and is potentially explosive. Dust
or powder may form explosive mixture with air. Soluble
compounds: alkali metals; sodium, potassium, molten
magnesium. Insoluble compounds: Violent reaction with
oxidizers, nitric acid; sulfuric acid. Forms explosive mixture
with potassium nitrate. Incompatible with oxidizers
(chlorates, nitrates, peroxides, permanganates, perchlorates,
chlorine, bromine, fluorine, etc.); contact may cause fires
or explosions. Keep away from alkaline materials, strong
bases, strong acids, oxoacids, epoxides.
Утилизация отходов
Recovery is indicated whenever
possible. Processes for recovery of Molybdenum from
scrap, flue dusts, spent catalysts and other industrial wastes
have been developed.
Молибден препаратная продукция и сырье
сырьё
препарат