The Applications of Cobalt

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As an important strategic metal with excellent physical, chemical and mechanical properties, cobalt is an important raw material for the production of materials with high temperature resistance, corrosion resistance, high strength and strong magnetism, therefore, it is widely used all over the world.

Pure cobalt is rarely used, but it is a main adding element for alloys and special steel. For example, the solid magnetic material is made of rare earth elements (mainly of samarium and erbium) and cobalt, and it is a permanent magnet with strong magnetic field. Similarly, cobalt is also added to the refractory alloys and super-hard corrosion resistant alloys. In many cases, cobalt is often used in the electroplating, because cobalt’s plating has much more stable weak acid resistance than that of chromium and nickel.

Cobalt is used most in a secondary battery. Cobalt’s applications have a larger growth in the battery field, mainly because the development of lithium-ion batteries. In information and communication industries as well as in the field of environmental protection and energy saving over today’s world, the lithium-ion battery is the latest generation of battery, with its specific energy, charge and discharge life higher than the Ni/MH batteries. Research and development of the lithium-ion secondary battery is extremely competitive, and developed countries place the synthesis of cathode material of lithium-ion secondary battery with superior electrochemical performance and favorable safety performance as a priority of the research and development. Developed cathode materials are lithium cobalt oxides or lithium nickel cobalt oxide or lithium cobalt oxide manganese. Cobalt oxide is applied to nickel-metal hydride batteries.

Due to excellent properties, cobalt is difficult to be replaced by other metals in the manufacture of heat-resistant alloys and corrosion-resistant alloys, so cobalt’s uses are still stable in the field of super alloys, and super alloy is currently the second largest area of cobalt applications. And cobalt has good wettability with many metals at high temperatures or low temperatures, so cobalt powder is widely used as a binder, which almost becomes irreplaceable matrix binder of diamond tools and cemented carbide. Chinese cemented carbide production ranks first in the world, as well as production of diamond tools is also the highest in the world.

Cobalt-based alloy is the general term of the alloy which is made of one or several metals among cobalt, chromium, tungsten, iron and nickel. Tool steels containing a certain amount of cobalt can dramatically improve the wear resistance of steels and cutting performance. Stellite containing cobalt over 50% never loses its original hardness even if heated to 1,000°C. At present, this cemented carbide has become the most important material for gold-bearing cutting tools. In this material, cobalt combines grains of other metal carbides in the alloy together, which makes the alloy with higher toughness and reduces the sensitivity performance to impact. And if this alloy melts and welds on the surface of parts, service life of parts can be enhanced by 3-7 times. Nickel-based alloys are the most widely used in the aerospace technology, and cobalt-based alloys as well, but these two have different “strength mechanisms”. Nickel-based alloys containing titanium and aluminum with high strength are because phase enhancers are composed in the form of NiAl (Ti). When operating at high temperatures, phase enhancer particles drift into a solid solution, and the alloy quickly loses their strength. As for cobalt-based alloys, they have heat resistance, because they form refractory carbides which don’t easily turn into the solid solution with a small diffusion activity; so the superiority of cobalt-based alloys will be shown comprehensively over 1,038°C, which is very suitable for the manufacture of high-temperature engines with high efficiency. Structural materials of aviation turbines using cobalt-based alloys containing chromium of 20%-27% can make materials with high resistance to oxidation without protective coatings. Cobalt-based alloy powder is widely used in the thermal spraying, for sealing surface and valve seat of an internal combustion engine exhaust valve, large bearings inner and outer rings of ships, large hydro turbine’s rotor blades, spray-fusing or spraying of the oil press propeller.

In addition, cobalt is one of few metals that can remain the magnetism by the magnetization once only. Under the action of heat, the temperature to lose magnetism calls the Curie point. Curie temperatures of iron and nickel are 769°C and 358°C respectively, while the curie temperature of cobalt is up to 1,150°C. Magnetic steel containing cobalt of 60% has the coercivity increased 2.5 times than that of common magnetic steel. Under the vibration, common magnetic steel loses almost one-third of magnetism while cobalt steel only loses 2%~3.5% of magnetism. So cobalt has an obvious advantage for magnetic materials. Metal cobalt nanopowder have a special role in the absorption of electromagnetic waves, and it can be used as military high-performance millimeter-wave stealth material, visible light infra-red stealth materials, and structure stealth materials as well as radiation shielding materials of mobile phone with iron, cobalt, zinc oxide powder and carbon-coated metal powder.