Refractory metals - General
Generally, speaking of "refractory metals" is to be understood that we are talking about metals, which have a very high melting point, it can reach 4000 ° C.Molybdenum, tantalum, tungsten, niobium and rhenium - basic refractory metals.Also this list can be added, and others - chromium, vanadium, osmium, hafnium, and zirconium metals, the melting temperature reaches 2123 ° C.
Refractory metals are interesting for their properties.Thus, for example, the hardness values of molybdenum and tungsten make it possible to use these metals for the heat treatment of materials under vacuum.Products from some refractory metals have unique properties, such as tungsten filament bulbs can withstand temperatures up to 3073 ° C.
But the resistance of refractory metals can be attributed to their main shortcomings.Contact with the oxygen significantly influences on the thermal properties of refractory metals.This is the reason the use of metals of the group - in an environment where they can be completely isolated from air.
Wolfram - the basis of refractory metals in metallurgy
Tungsten is one of the most refractory metals.The melting point of tungsten is higher than others, tungsten - a heavy metal, it can be pulled out of thin filaments, and it is perfectly weldable.Tungsten is a rare metal, as its content in the crust reaches only 0.0055%, it was not found in the solar spectrum, and it is not in sea water.But its popularity is not inferior to the metal less rare metals.
use tungsten
metal tungsten is used for the production of filaments, which are used in lighting, heating element - in vacuum furnaces resistance.The high density of tungsten allows the use of the metal as a counterweight to the various shells.Tungsten is used as the electrode during the TIG welding.The tungsten carbide is used as filler.
tungsten as molybdenum, and tantalum is used as a rule in the alloys used in the details space nuclear technology.The ability to withstand very high temperatures - the main purpose for which they were established, these alloys.
