Tantalum, niobium, tungsten, and molybdenum are all refractory metals, which means they have high melting points and are highly resistant to corrosion and wear. However, they have different physical properties that make them more suitable for certain applications.
Comparison of refractory metal’s properties:
Density: Tungsten has the highest density of the four metals, at 19.3 g/cm³, followed by tantalum (16.6 g/cm³), niobium (8.57 g/cm³), and molybdenum (10.2 g/cm³).
Melting Point: Tungsten has the highest melting point of the four metals, at 3,422 °C, followed by tantalum (3,020 °C), molybdenum (2,623 °C), and niobium (2,468 °C).
Machinability: Niobium is the easiest to machine of the four metals, followed by tantalum, molybdenum, and tungsten. Tungsten, in particular, is very difficult to machine due to its high hardness and brittleness. Tungsten Heavy Alloywould be an alternative with improved machinability.
Corrosion Resistance: Tantalum has excellent corrosion resistance, especially in acidic environments, making it well-suited for chemical processing and medical implants. Niobium is also highly corrosion resistant, while tungsten and molybdenum are more prone to corrosion.
Price: Tantalum is the most expensive of the four metals, followed by niobium, tungsten and molybdenum.
Thermal Conductivity: Tungsten has the highest thermal conductivity of the four metals, followed by molybdenum, tantalum, and niobium. This property can be important for heat management in some applications.
Ductility: Niobium and tantalum are both highly ductile, which means they can be drawn into wires or formed into various shapes without breaking. Tungsten and molybdenum are less ductile, but they have excellent resistance to bending and stretching.
Electrical Conductivity: Tungsten and molybdenum have lower electrical conductivity than tantalum and niobium. This can be important for applications where electrical resistance is required, such as heating elements.
Appearance: Niobium has a unique surface coloration when anodized, and it can be anodized to produce a wide range of colors. This makes it popular for use in jewelry and other decorative applications.
Environmental Impact: Tungsten and molybdenum are both more abundant than tantalum and niobium, and they are often mined from countries with fewer environmental regulations. This can make them a more environmentally friendly choice for some applications.
When choosing a material for a specific application, the following factors should be considered:
- Operating environment: The operating temperature and chemical environment will determine the level of corrosion resistance required.
- Mechanical properties: The required strength and toughness of the material should be considered.
- Machinability: If the part requires machining, the ease of machining should be considered.
- Cost: The cost of the material should be balanced against its suitability for the application.
Applications where each of these metals is commonly used:
- Tantalum: Chemical processing, medical implants, and electronic components.
- Niobium: Aerospace components, superconductors, and medical implants.
- Tungsten: Electrical contacts, welding electrodes, and radiation shielding.
- Molybdenum: Aerospace components, heating elements, and glass melting electrodes.
|Admat’s Refractory Metals Max Temp in Open Air w/ Limited Oxidation Risk|
|Metal||Maximum Temperature in Air|
|Niobium*||Up to XXX °C|
|Tungsten||Up to 400°C|
|Molybdenum||Up to 500°C|
*As an alternative to niobium, Admat’s Niobium Hafnium Titanium (C-103) has a much higher operating temperature in open air.
Note: These temperatures are approximate and can vary depending on factors such as the purity of the material, the surface condition, and the environment in which it is being used. It’s important to consult with a materials engineer or other expert to determine the most appropriate materials and operating conditions for a given application.
Overall the choice of material depends on the specific requirements of the application. Tantalum and niobium are good choices for applications that require high corrosion resistance, while tungsten and molybdenum are better suited for applications that require high strength, high melting point, or electrical resistance.