Nickel magnetism

Figure 6. Ordered nickel magnetic moments vs staggered magnetic field directed along the nickel chain. Both quantities are estimated from the spectroscopically measured ground-state splitting of Er3+ in (ErxY1.x)2BaNi05.

Other methods that have been used to determine include dynamic mechanical analysis [102,103, 108-110], dielectric thermal analysis [102], nickel magnetic resonance spectrometry [111-116], and inverse gas chromatography [117,118]. 

Figure Cl.1.5. Nickel cluster magnetic moment per atom (p) as a function of cluster size, at temperatures between 73 and 198 K. Apsel S E, Emmert J W, Deng J and Bloomfield L A 1996 Phys. Rev. Lett. 76 1441, figure 1.

Billas I M L, Chatelain A and de Heer W A 1994 Magnetism from the atom to the bulk in iron, cobalt, and nickel clusters Science 265 1682... 

Within the periodic Hartree-Fock approach it is possible to incorporate many of the variants that we have discussed, such as LFHF or RHF. Density functional theory can also be used. I his makes it possible to compare the results obtained from these variants. Whilst density functional theory is more widely used for solid-state applications, there are certain types of problem that are currently more amenable to the Hartree-Fock method. Of particular ii. Icvance here are systems containing unpaired electrons, two recent examples being the clci tronic and magnetic properties of nickel oxide and alkaline earth oxides doped with alkali metal ions (Li in CaO) [Dovesi et al. 2000]. 

It is alloyed with iron, nickel and other metals to make Alnico, an alloy of unusual magnetic strength with many important uses. Stellite alloys, containing cobalt, chromium, and tungsten, are used for high-speed, heavy-duty, high temperature cutting tools, and for dies. 

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. 

The treatments used to recover nickel from its sulfide and lateritic ores differ considerably because of the differing physical characteristics of the two ore types. The sulfide ores, in which the nickel, iron, and copper occur in a physical mixture as distinct minerals, are amenable to initial concentration by mechanical methods, eg, flotation (qv) and magnetic separation (see SEPARATION,MAGNETIC). The lateritic ores are not susceptible to these physical processes of beneficiation, and chemical means must be used to extract the nickel. The nickel concentration processes that have been developed are not as effective for the lateritic ores as for the sulfide ores (see also Metallurgy, extractive Minerals recovery and processing). 

The matte can be treated in different ways, depending on the copper content and on the desired product. In some cases, the copper content of the Bessemer matte is low enough to allow the material to be cast directly into sulfide anodes for electrolytic refining. Usually it is necessary first to separate the nickel and copper sulfides. The copper—nickel matte is cooled slowly for ca 4 d to faciUtate grain growth of mineral crystals of copper sulfide, nickel—sulfide, and a nickel—copper alloy. This matte is pulverized, the nickel and copper sulfides isolated by flotation, and the alloy extracted magnetically and refined electrolyticaHy. The nickel sulfide is cast into anodes for electrolysis or, more commonly, is roasted to nickel oxide and further reduced to metal for refining by electrolysis or by the carbonyl method. Alternatively, the nickel sulfide may be roasted to provide a nickel oxide sinter that is suitable for direct use by the steel industry. 

Nickel Oxalate. This salt, NiC204, mol wt 146.7, is produced as a greenish white crystalline dihydrate [6018-94-6]. It decomposes by heating at 320°C under vacuum into Ni metal and carbon dioxide. Nickel oxalate is used for the production of nickel catalysts and magnetic materials. 

Cobalt. There is no U.S. mine production of cobalt. Refining of imported nickel—cobalt mattes has not occurred since the mid-1980s. About 1600 t of secondary cobalt was recycled from scrap by 13 faciUties in the United States representing - 22% of total U.S. consumption. The price of the metal was around 44/kg. Most is imported from Zaire and Zambia. Increasing quantities are coming from Russia. Historically, the price of cobalt has been quite volatile and dependent on the pohtical environment in those countries. Cobalt is used in superaHoys, 40% catalysts, 14% paint driers, 11% magnetic alloys, 10% and cemented carbides and other uses, 16%. 

Selenium is added up to 0.1% to silicon steels (2—4% Si) used in transformer cores to enhance the development of the secondary recrystallization texture which, in turn, improves the magnetic characteristics. Selenium alloying additions to the melt may be made as elemental Se, nickel—selenium, or ferroselenium. The recovery depends on the melting practice and method of addition. Normally, it is in the range of 66%, but may be as high as 90%. 

Nickel—Iron and Cobalt—Iron Alloys. Selenium improves the machinabifity of Ni—Ee and Co—Ee alloys which are used for electrical appfications. Neither sulfur nor tellurium are usefiil additives because these elements cause hot britdeness. The addition of 0.4—0.5% selenium promotes a columnar crystal stmcture on solidification, doubling the coercive force of cobalt—iron-titanium alloy permanent magnets produced with an equiaxial grain stmcture. 

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