The use of metallic cobalt

Cobalt is mainly used to make alloys. Cobalt-based alloys are the general names of alloys made of cobalt and one or more of chromium, tungsten, iron and nickel. Tool steel containing a certain amount of cobalt can significantly improve the wear resistance and cutting performance of steel. Stellite containing more than 50% cobalt will not lose its original hardness even if it is heated to 1000℃. Nowadays, this kind of cemented carbide has become the most important material used between gold-bearing tools and aluminum. In this material, cobalt combines with other metal carbide grains in the alloy composition, which makes the alloy have higher toughness and reduces the sensitivity to impact. This alloy is welded on the surface of parts, which can improve the service life of parts by 3-7 times. The most widely used alloy in aerospace technology is nickel-based alloy, and cobalt-based alloy can also be used, but the "strength mechanism" of the two alloys is different. The high strength of nickel-based alloys containing titanium and aluminum is due to the formation of phase strengthening agent with NiAl(Ti). When the operating temperature is high, the phase enhancer particles become solid solution, and the alloy soon loses strength. The heat resistance of cobalt-based alloys is due to the formation of refractory carbides, which are not easy to be converted into solid solutions and have low diffusion activity. When the temperature is above 1038℃, the advantages of cobalt-based alloys are fully demonstrated. This is just right for manufacturing high-efficiency high-temperature engines, and so is the cobalt-based alloy. Using cobalt-based alloy containing 20%-27% chromium in the structural material of aviation turbine can make the material achieve high oxidation resistance without protective coating. The turbine generator with mercury as heat medium supplied by nuclear reactor can run continuously for more than one year without maintenance. It is reported that the boilers of generators used in the United States are made of cobalt alloy. Cobalt is one of the few metals that can remain magnetic after being magnetized. Under the action of heat, the temperature at which magnetism is lost is called Curie point. The Curie point of iron is 769℃, nickel is 358℃, and cobalt can reach 1 150℃. The coercivity of magnetic steel containing 60% cobalt is 2.5 times higher than that of general magnetic steel. Under vibration, general magnetic steel loses almost 1/3 magnetism, while cobalt steel only loses 2%-3.5% magnetism. Therefore, the advantages of cobalt in magnetic materials are obvious. Cobalt is also widely used in electroplating, glass, dyeing, medicine and medical treatment. Lithium cobaltate made of lithium carbonate and cobalt oxide is the most widely used cathode material for modern high-energy batteries. Cobalt may also be used to make nuclear weapons, a theoretical atomic bomb or hydrogen bomb, which is packed in a cobalt shell and can turn cobalt into deadly radioactive dust after explosion.