Login for faster access to the best deals. Click here if you don't have an account.

Element History - Brief Review Professional

1 month ago Multimedia Battambang   12 views

$ --

  • img
Location: Battambang
Price: $ --

Element History - Brief Review

Tungsten is a heavy metallic element, a member of the third series of transition metals. It has the symbol W, its atomic number is 74, and its atomic weight is 183.85. The name is derived from the Swedish tung sten, meaning “heavy stone.” Tungsten is also known as wolfram, from WOLFRAMITE, the mineral from which the element was first recognized by the English chemist Peter Woulfe in 1779. The metal was first isolated in 1783 by Spanish scientists Jose and Fausto d’Elhuyar through the reduction, by means of charcoal, of the tungstic acid found in wolframite.

Tungsten occurs principally in the minerals scheelite, wolframite, huebnerite, and ferberite. In the United States these minerals occur most notably in California and Colorado. Elsewhere they are found in China, the Buryat republic of Russia, Kazakhstan, South Korea, Bolivia, and Portugal. The metal is obtained commercially by the reduction of tungstic oxide with hydrogen or carbon. The pure metal is steel gray to tin white in color. Its physical properties include the highest melting point of all metals, 3,410 deg C (6,170 deg F), a boiling point of 5,660 deg C (10,220 deg F), and a density of 19.3 g/cu cm.

Pure tungsten metal is easily forged, spun, drawn, and extruded, whereas in an impure state it is brittle and can be fabricated only with difficulty. Tungsten oxidizes in air, especially at higher temperatures, but it is resistant to corrosion and is only slightly attacked by most mineral acids. In keeping with the other Transition Elements, it displays a range of oxidation states: 0, +1, +2, +3, +4, +5, and +6. This accounts for the many complex ions and coordination complexes in which tungsten can be found. Tungsten is not known to have any biological significance.

TUNGSTEN PLATE

Tungsten plate sheet is isostatically pressed and sintered from our high purity tungsten powders to compact ingots by powder metallurgy. Following the powder metallurgy is a series of further deformations and heat treatments until the required products are finished. We are now capable of machining tungsten plate and sheet with a range of thickness from 3.15 inches (80 mm) to less than 0.004 inches (0.1 mm).

CHEMETAL USA is a recognized manufacturer and supplier of high quality tungsten plate and tungsten sheet. Every tungsten plate we supply is under stringent quality control at every stage of production, including the rolling, annealing, surface treatment and a series of tests. Thanks to our experience and capacity in the field of milling tungsten product, we can always guarantee that our customers receive high-performance tungsten plate products with exceptional purity, roughness, dimension, flatness and surface condition.

Zirconium

Zirconium is abundant in S-type stars in which heavier elements are formed by neutron capture. Traces of the element are also present in the Sun, and rock brought back from the moon was found to have a surprisingly high zirconium content.

Down here on Earth scientists have recently discovered that zircons from the Jack Hill region of Western Australia were around 4.4 billion years old and this together with their oxygen isotope ratio of O16/O18 suggested that they could only have been formed when there was liquid water on the surface of the Earth, which is nearly 500 million years earlier than previously assumed.

Today the element is widely used, as zircon (zirconium silicate), zirconium oxide and as the metal itself.

Zircon sand is use for foundry equipment - in the heat-resistant linings for furnaces and to make foundry moulds and giant ladles. Mixed with vanadium or praseodymium, zircon makes blue and yellow pigments for glazing pottery and tiles.

Zirconium oxide, with a melting point of 2715oC, is used to make heat-resistant crucibles, ceramics and abrasives. A red-hot crucible made from ZrO2 can be plunged into cold water without cracking. Zirconium oxide is stronger than toughened steel and is also used for knives, scissors and golf irons. The production of pure zirconium oxide is ca 25,000 tonnes per year, some of which goes into other products, including cosmetics, antiperspirants, food packaging, and even fake gems. The paper and packaging industry finds that zirconium oxide makes good surface coatings because it has excellent water resistance and strength, and is non-toxic.

Hafnium

Hafnium is dispersed in Earth’s crust to the extent of three parts per million and is invariably found in zirconium minerals up to a few percent compared with zirconium. For example, the minerals zircon, ZrSiO4 (zirconium orthosilicate), and baddeleyite, which is essentially pure zirconium dioxide, ZrO2, generally have a hafnium content that varies from a few tenths of 1 percent to several percent. Altered zircons, like some alvites and cyrtolites, products of residual crystallization, show greater percentages of hafnium (up to 17 percent hafnium oxide in cyrtolite from Rockport, Mass., U.S.). Commercial sources of hafnium-bearing zirconium minerals are found in beach sands and river gravel in the United States (principally Florida), Australia, Brazil, western Africa, and India. Hafnium vapour has been identified in the Sun’s atmosphere.