| LC control no. | sh 85113607 |
|---|---|
| LC classification | QD181.R4 General and inorganic chemistry QD412.R4 Organometallic chemistry QD464.R4 Atomic and molecular weights QE516.R4 Geochemistry TA480.R5 Engineering materials |
| Topical heading | Rhenium |
| Variant(s) | Dvi-manganese |
| See also | Manganese group |
| Found in | Wikipedia, Mar. 12, 2013 (Refractory 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: two of the fifth period (niobium and molybdenum) and three of the sixth period (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. Most definitions of the term 'refractory metals' list the extraordinarly high melting point as a key requirement for inclusion. By one definition, a melting point above 4,000 °F (2,200 °C) is necessary to qualify. The five elements niobium, molybdenum, tantalum, tungsten and rhenium are included in all definitions, while the wider definition, including all elements with a melting point above 2,123 K (1,850 °C), includes a varying number of nine additional elements, titanium, vanadium, chromium, zirconium, hafnium, ruthenium, osmium and iridium. Transuranium elements (those above uranium, which are all unstable and not found naturally on earth) and technetium are never considered to be part of the refractory metals.) Chemicool website, Mar. 12, 2013 (Rhenium; transition metal; Russian chemist Dmitri Mendeleev created the periodic table in 1869. From gaps he saw in the table, Mendeleev predicted the existence of undiscovered elements. He said two of the elements he had predicted would have similar properties to manganese. He called these eka-manganese, now technetium, and dvi-manganese, now rhenium. Rhenium is one of the five major refractory metals (metals with very high resistance to heat and wear).) |
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