Refractory metals refer to a class of substances with good electrical and thermal conductivity that possess a very high melting point of greater than 2000°C (3632°F). They are strongly resistant to wear, deformation and corrosion.
With their extremely high melting points, these metals can withstand creep deformation when subjected to extremely high temperatures. Refractory metals are commonly used in metallurgy, material science and engineering.
Five main types of refractory metal elements are used in industrial corrosion-preventative activities. They are:
- Molybdenum (Mo)
- Niobium (Nb)
- Rhenium (Re)
- Tantalum (Ta)
- Tungsten (W)
These elements possess similar electronic structures to one another - characterized by transition elements with incomplete D sub-shells on the subatomic microscopic level.
The high melting point of these metals make them uniquely equipped with strength, hardness, resistance to corrosion, resistance to heat and minimal reactivity with water. The above listed metals are used to fabricate tools, casting molds, wire filaments and nuclear reaction control rods. Due to their high melting point, they are never fabricated by casting but rather by powder metallurgy.
Molybdenum, tantalum and tungsten have higher melting points and can be useful in glass making and the processing of molten metals. Tungsten also has outstanding strength.
Refractory metals have exceptional corrosion resistance. Due to this, piping in chemical plants often consists of refractory metals. These metals also offer excellent abrasion and wear resistance, especially in alloy form. For instance, refractory metals that are in alloy form can prolong the lifespan of:
- Valve seats
- High water points