Search results
Results From The WOW.Com Content Network
Tungsten (also called wolfram) [14] [15] is a chemical element; it has symbol W and atomic number 74. It 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.
The Gmelin rare earths handbook lists 1522 °C and 1550 °C as two melting points given in the literature, the most recent reference [Handbook on the chemistry and physics of rare earths, vol.12 (1989)] is given with 1529 °C.
Refractory metals have high melting points, with tungsten and rhenium the highest of all elements, and the other's melting points only exceeded by osmium and iridium, and the sublimation of carbon. These high melting points define most of their applications. All the metals are body-centered cubic except rhenium which is hexagonal close-packed.
The hardness of osmium is moderately high at 4 GPa. Because of its hardness, brittleness, low vapor pressure (the lowest of the platinum-group metals), and very high melting point (the fourth highest of all elements, after carbon, tungsten, and rhenium), solid osmium is difficult to machine, form, or work.
The elements in the group, like those of groups 7–11, have high melting points, and form volatile compounds in higher oxidation states. All the elements of the group are relatively nonreactive metals with a high melting points (1907 °C, 2477 °C, 3422 °C); that of tungsten is the highest of all metals.
Of the group 9 elements, only cobalt has a biological role. It is a key constituent of cobalamin , also known as vitamin B 12 , the primary biological reservoir of cobalt as an ultratrace element . [ 21 ] [ 22 ] Bacteria in the stomachs of ruminant animals convert cobalt salts into vitamin B 12 , a compound which can only be produced by ...
The free element, a silvery metal with a grey cast, has the sixth-highest melting point of any element. It readily forms hard, stable carbides in alloys, and for this reason most of the world production of the element (about 80%) is used in steel alloys, including high-strength alloys and superalloys. Most molybdenum compounds have low ...
Most of the chemistry has been observed only for the first three members of the group (the chemistry of dubnium is not very established, but what is known appears to match expectations for a heavier congener of tantalum). All the elements of the group are reactive metals with a high melting points (1910 °C, 2477 °C, 3017 °C).