Cobalt (Co)
Cobalt is a critical strategic metal essential for superalloys, cemented carbides, rechargeable batteries, and magnetic materials. Its ability to maintain strength at extreme temperatures makes it irreplaceable in jet engine and gas turbine components, while its electrochemical properties drive the lithium-ion battery revolution.
Properties
- Density
- 8,900 kg/m³
- Melting Point
- 1,495 °C
- Boiling Point
- 2,927 °C
- Thermal Conductivity
- 100 W/(m·K)
- Electrical Resistivity
- 6.24 × 10⁻⁸ Ω·m
- Tensile Strength
- 760–1,200 MPa
- Yield Strength
- 450–900 MPa
- Hardness
- 125–350 HB
- Elongation
- 5–25%
- Crystal Structure
- HCP (α) / FCC (β)
Common Grades
- Stellite 6 (CoCrW): Cobalt-chromium-tungsten hardfacing alloy. Valves, cutting tools, wear surfaces.
- Stellite 21 (CoCrMo): Cobalt-chromium-molybdenum alloy. Medical implants, dental prosthetics.
- L605 (Co-20Cr-15W-10Ni): High-temperature sheet alloy. Gas turbine combustion chambers, afterburners.
- MP35N (Co-35Ni-20Cr-10Mo): Ultrahigh-strength alloy. Fasteners, springs, medical devices, subsea components.
Applications
- Batteries: Lithium-ion cathodes (LCO, NMC, NCA), portable electronics, electric vehicles
- Superalloys: Jet engine vanes, turbine blades, combustion chambers, industrial gas turbines
- Cutting Tools: Cemented carbide binder (WC-Co), diamond tool binder, hardfacing alloys
- Medical: Hip/knee implants (CoCrMo), dental alloys, surgical instruments
- Magnets: Samarium-cobalt (SmCo) permanent magnets, AlNiCo magnets
FAQ
Why is cobalt important for electric vehicles?
Cobalt is a key cathode material in lithium-ion batteries. In NMC (nickel-manganese-cobalt) and NCA (nickel-cobalt-aluminum) chemistries, cobalt stabilizes the crystal structure, preventing thermal runaway. While the industry is reducing cobalt content per cell, total demand is rising as EV production scales exponentially.
What are the ethical concerns with cobalt?
Approximately 70% of global cobalt comes from the Democratic Republic of Congo, where artisanal mining has been linked to child labor and unsafe conditions. Major manufacturers now require supply chain auditing per OECD Due Diligence Guidance. Recycling and cobalt-free battery chemistries (LFP) are being developed as alternatives.
What is Stellite and why is it used for valve seats?
Stellite is a cobalt-chromium-tungsten alloy family that maintains hardness (38–55 HRC) at temperatures up to 800°C, resists corrosion, erosion, and galling. Stellite 6 hardfacing on valve seats provides 10–50× longer life than stainless steel in high-temperature, high-pressure steam and chemical service.