Spotlight on Cobalt: Wire, Foil and Rod for Research

Cobalt is a transition metal with a melting point of approximately 1,495 °C. Like iron and nickel, it is ferromagnetic at room temperature, and it stays ferromagnetic up to a Curie temperature of approximately 1,120 °C.

Researchers use cobalt for its magnetic behaviour and in high-temperature and wear-resistant alloys. 
Advent Research Materials supplies it as foil, wire and rod, in purities from 99.9% to 99.998+%. 

This overview covers its physical properties, its research uses and the specifications available.

Cobalt has atomic number 27 and a density of approximately 8.9 g/cm³. 
At room temperature its Young's modulus is about 209 GPa, its electrical resistivity around 6 × 10⁻⁸ Ω·m and its thermal conductivity roughly 100 W/(m·K), although resistivity and conductivity vary with temperature and material condition. 
Its room-temperature crystal structure is hexagonal close-packed (hcp), which changes to face-centred cubic (fcc) at approximately 417 °C. The hcp structure has fewer readily available slip systems than fcc metals such as nickel and copper, which contributes to cobalt's more limited ductility. 
Temperature, grain structure, impurities and processing history also affect it.

Solid cobalt is relatively inert in air at room temperature, but oxidation becomes extensive above about 300 °C. It dissolves slowly in dilute mineral acids. Handling precautions depend on the form of the material, so follow the relevant safety data sheet.

Where cobalt is used in research

Several of these uses rely on cobalt alloys, whose properties do not carry over to elemental cobalt wire, foil or rod.

Choosing the right form

Advent supplies cobalt in three forms. The most suitable depends on the dimensions, shape and mechanical properties the work requires.

Annealing reduces hardness and generally increases ductility, making cobalt easier to bend and form. Cold working during drawing generally raises strength and hardness and reduces ductility. Actual properties depend on processing history, so check them against the individual product specification.

Choosing the right purity

Listed purities run from 99.9% for the foil to 99.998+% for one 1 mm annealed wire, and most wire lines are 99.95%.

The melting route is relevant to processing and impurity control, but the route alone does not establish the final impurity profile. Nominal purity has a similar limit. A 99.99% product is not automatically a better choice than a 99.95% one, because that depends on which impurities matter to the experiment.

Some product pages give an impurity analysis. The analysis shown for one batch of the 0.25 mm annealed wire, for example, records nickel at 300 ppm, its largest listed impurity. Where composition is critical, check the individual product specification for its melting route and any available analysis, and compare these with your experimental requirements.