Definition - What does Refractory Metals mean?
Refractory metals are a group of metal elements or alloys that have exceptionally high melting points, greater than 2000°C, and are resistant to wear, corrosion and deformation.
Corrosionpedia explains Refractory Metals
Refractory metals are not encountered in nature.
The five refractory metals are:
- Molybdenum (Mo)
- Niobium (Nb)
- Rhenium (Re)
- Tantalum (Ta)
- Tungsten (W)
Refractory metals, which have similar electronic structures, are transition elements with incomplete D sub-shells. Not only the outer S electrons, but also the D electrons participate in the interatomic bonds of refractory metals, which accounts for the great strength of these bonds and, hence, the metals’ high melting point, mechanical strength and hardness, as well as resistance to corrosion.
The identifying feature of refractory metals is their resistance to heat. The five industrial refractory metals all have melting points in excess of 3632°F (2000°C). The strength of refractory metals at high temperatures, in combination with their hardness, makes them ideal for cutting and drilling tools. Refractory metals are also very resistant to thermal shock, meaning that repeated heating and cooling will not easily cause expansion, stress or cracking. The metals all have high densities as well as good electrical and heat conducting properties. Another important property is their resistance to creep, the tendency of metals to slowly deform under the influence of stress. Owing to their ability to form a protective layer, the refractory metals are also resistant to corrosion, although they do readily oxidize at high temperatures.
Refractory metals are used in lighting, tools, lubricants, nuclear reaction control rods, as catalysts, and for their chemical or electrical properties. Because of their high melting point, refractory metal components are never fabricated by casting. Instead, the process of powder metallurgy is used.