Cobalt -based magnetic alloys

Overall, this is the most significant use of cobalt, as shown in Table I (48% total use). Metallic cobalt is an important alloying element in numerous applications, such as super alloys (cobalt, nickel, iron based), magnetic alloys (soft, AlNiCo, SmCo), wear-resistant alloys, high speed steels, prosthetic alloys, and cemented carbide. 

Table4.3-22 Physical and magnetic properties of the cobalt-based amorphous alloy METGLAS alloy 2714 AF [3.22]...

Soft magnetic materials are characterized by high permeabiUty and low coercivity. There are sis principal groups of commercially important soft magnetic materials iron and low carbon steels, iron—siUcon alloys, iron—aluminum and iron—aluminum—silicon alloys, nickel—iron alloys, iron-cobalt alloys, and ferrites. In addition, iron-boron-based amorphous soft magnetic alloys are commercially available. Some have properties similar to the best grades of the permalloys whereas others exhibit core losses substantially below those of the oriented siUcon steels. Table 1 summarizes the properties of some of these materials. 

Explain in terms of your answer to Problem 3 why many of the hard magnetic alloys are based on cobalt. 

High-purity metals and superalloys are required for the aeronautics, electronics, instruments, space, and defense industries the raw materials are at present imported. Primarily, these special metals include nickel-and cobalt-based superalloys, high-strength iron-based alloys, titanium-based alloys, controlled-expansion alloys, and magnetic materials. Keeping in view the importance of these metals and alloys and the expertise available in India for making them, the NCST has identified two projects for their development the setting up of a special metal and superalloys plant and the development of controlled-expansion alloys. 

A wide variety of metals is produced for industries such as automotive, aerospace, marine, energy, chemical processing, etc. Materials include aluminum, titanium, stainless steel, nickel- and cobalt-base alloys, tool steels, and materials for electronic, magnetic, and expansion applications. Regardless of the metal, the stime selection process can be used. 

Cobalt is a metal with magnetic properties similar to those of iron. Its salts give glass a beautiful deep-blue colon Cobalt-based alloys have long been used in the manufacturing industry. An addition of 20% cobalt to chromium-nickel-based alloys, used for turbine blades and burner lines in aircraft engines, improves the high-temperature properties. Cobalt powder is an important component in cemented carbides (hard metals). Cobalt is also an essential element for life and important for humans and animals. It is present mainly in the form of vitamin Bjj. The artificially produced isotope Co is used as a source of intense g-radiation. It is used in industry and in radioisotope therapy. 

An obvious refinement of the simple theory for cobalt and nickel and their alloys can be made which leads to a significant increase in the calculated value of the Curie temperature. The foregoing calculation for nickel, for example, is based upon the assumption that the uncoupled valence electrons spend equal amounts of time on the nickel atoms with / = 1 and the nickel atoms with J = 0. However, the stabilizing interaction of the spins of the valence electrons and the parallel atomic moments would cause an increase in the wave function for the valence electrons in the neighborhood of the atoms with / = 1 and the parallel orientation. This effect also produces a change in the shape of the curve of saturation magnetization as a function of temperature. The details of this refined theory will be published later. 

Important is the use of light rare earth elonents for production of hard magnetic materials. Most prominent are alloys of samarium with cobalt in the atomic ratio 1 5 or 2 17. It may also be assumed that in further development of these materials on a larger scale that praseodymium, neodymium, lanthanum and also individual heavy rare ecu h elements will be used to achieve particular effects. Interesting is the development of magnetic bubble memories based on gadolinium-galliiimrgarnets. 

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