According to Encyclopaedia Britannica, a refractory material is any material that has a very high melting point, allowing it to maintain its structure even in extreme temperatures.
This applies to refractory metals, too. However, ScienceDirect goes further to specify that refractory metals don’t just have a high melting point, but also possess ‘other special physical and chemical properties’ – including chemical inertness and corrosion resistance.
Using a generic definition, there are many metals that could be considered refractory – yet there are only a few that are widely named and sold specifically as refractory metals.
Let’s look into the most commonly known refractory metals, as well as their common properties and applications, and where they can be found.
Primary refractory metals
There is no definitive melting point that officially classifies a metal as refractory, but most sources set a threshold of >2,450°C, leaving the following five metals in this category:
- Tungsten (W) – melting point 3,410°C
- Rhenium (Re) – melting point 3,180°C
- Tantalum (Ta) – melting point 2,996°C
- Molybdenum (Mo) – melting point 2,610°C
- Niobium (Nb) – melting point 2,468°C
These undisputed refractory metals also have very high boiling points, densities, and hardness, making them extremely resistant to wear and deformation.
Secondary refractory metals
There are several other metals with high melting points that could also be called refractory metals if the threshold was lowered to >1,650°C, including these platinum, transition, and noble metals:
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- Iridium (Ir) – melting point 2,410°C
- Ruthenium (Ru) – melting point 2,250°C
- Hafnium (Hf) – melting point 2,227°C
- Rhodium (Rh) – melting point 1,966°C
- Vanadium (V) – melting point 1,890°C
- Chromium (Cr) – melting point 1,890°C
- Zirconium (Zr) – melting point 1,890°C
- Platinum (Pt) – melting point 1,769°C
- Titanium (Ti) – melting point 1,660°C
While Osmium (Os) has a melting point of 3,000°C, its oxides are toxic. Similarly, Technetium (Tc) has a melting point of 2,172°C and Thorium (Th) has a melting point of around 1,700°C, but these aren’t practical choices due to their radioactivity.
Many of these metals also don’t fit the stricter definition due to weaker properties such as lower densities, or they simply aren’t widely used due to rarity and higher costs.
Common refractory metal properties
The main beneficial property of a refractory metal is its high melting point, but this also lends these metals a range of other advantageous characteristics, including high boiling points, and the ability to hold their shape under heat and pressure (known as creep resistance).
This is also due to the high density, tensile strength, and hardness of refractory metals, making them incredibly robust and guaranteeing durability even in the most challenging environments.
This special category of metals is also capable of conducting electrical currents and heat without thermal shock, as these materials can withstand high temperatures without expanding or cracking.
Though they oxidise easily, the stable outer layer of oxides gives refractory metals a high level of corrosion resistance that makes them resistant to most acids.
Common refractory metal applications
Their superior strength and resistant qualities make refractory metals ideal materials for use in a wide range of demanding applications. These uses include (but are not limited to):
- Electronics, semiconductors, and superconductors
- Industrial parts (e.g. furnaces, crucibles, dies)
- Medical devices (e.g. scanners and radiation shields)
- Aerospace (e.g. jet engines and thruster nozzles)
- Nuclear reactors (e.g. structural components and radiation shielding)
- Superalloys (e.g. strengthening metals for structural tubing)
- Chemicals (e.g. catalysts and anti-corrosion coatings)
- Powder metallurgy (creating metals from elements in powder form)
In many of these settings, only the strongest materials with the highest levels of resistance are appropriate, as using weaker materials would pose too great of a safety risk.
In addition to having the highest melting point of all metals, tungsten metal is one of the most commonly used refractory materials.
While it’s most well-known historically for its use in incandescent light bulbs filaments, it’s also frequently used in welding electrodes and heating elements in furnaces.
Ordering refractory metals online
Most of the primary five refractory metals can easily be ordered in bulk online, and are typically available in various forms such as wires, rods, strips, sheets, bars, and crucibles.
You can find these metals in standard sizes or order bespoke dimensions through an industry specialist, such as Special Metals, who is a trusted supplier of tungsten in the UK.
The shapes, sizes, and quantities required will, of course, depend on the purpose and scale of your intended application – but available products and quotes can be provided on request.
