Nickel ferrites

The barium ferrite was found to have an increase in magnetic anisotropy, as in the nickel ferrite, but its overall effect on magnetization was less because of greater magnetocrystalline anisotropy. The shock modification caused reduced crystallite size and local damage that resulted in increased microwave absorption. 

Sintered and sprayed ceramic anodes have been developed for cathodic protection applications. The ceramic anodes are composed of a group of materials classified as ferrites with iron oxide as the principal component. The electrochemical properties of divalent metal oxide ferrites in the composition range 0- lA/O-0-9Fe2O3 where M represents a divalent metal, e.g. Mg, Zn, Mn, Co or Ni, have been examined by Wakabayashi and Akoi" . They found that nickel ferrite exhibited the lowest consumption rate in 3% NaCl (of 1 56 g A y at 500 Am and that an increase in the NiO content to 40mol 7o, i.e. O NiO-O-bFejO, reduced the dissolution rate to 0-4gA y at the expense of an increase in the material resistivity from 0-02 to 0-3 ohm cm. 

The scheme E involves dead roasting of the concentrate by which Fe203 forms and the nickel content is oxidized to nickel ferrite (NiFe204). This material is selectively reduced to produce an iron-nickel alloy which is then leached in an ammoniacal ammonium carbonate solution for nickel recovery, leaving hematite as a leach residue. 

Nickel dioxide, 77 107 Nickel double salts, 77 113 Nickel electrodes, 3 430 72 216 Nickel electroplating solutions, 9 818t Nickel extraction, 70 791 Nickel ferrite brown spinel, formula and DCMA number, 7 348t Nickel fibers, 77 108 Nickel fluoride complexes, 77 111 Nickel fluoride tetrahydrate, 77 109-110 Nickel fluoroborate, 77 111 Nickel fluoroborate hexahydrate, 4 157t, 158, 159... 

Few comparative studies have been made on the reductive dissolution of different mineral phases. In one such study, the order of reaction with seven organic and transition metal reductants was found to be the same hematite (a-Fe203)>magnetite (FejO,/,)>nickel ferrite (NiFe204) (43). Magnetite is an interesting case, since both Fe(III) and Fe(II) are present in the lattice prior to reaction. Evidence indicates that Fe(IIl) sites reduced to Fe(II) sites by redox reaction dissolve more quickly than Fe(II) sites originally present in the mineral lattice (6). 

Regazzoni, A.E. Matijevic, F. (1983) Formation of uniform colloidal mixed cobalt nickel ferrite particles. Colloids Surfaces 6 189—... 

Segal, M.G. Sellers, R.M. (1982) Kinetics of metal oxide dissolution. Reductive dissolution of nickel ferrite by tris (picolinato) vana-dium(ll). J. Chem. Soc. Faraday Trans. 1. 78 1149-1164... 

Precipitation can remove soluble nickel Ifom water. In aerobic waters, nickel ferrite is the most stable compound (Rai and Zachara 1984). Nickel may also be removed by coprecipitation with hydrous iron and manganese oxides. Nickel removed by precipitation and coprecipitation settles into the sediment. 

An analysis of the thermodynamic stability models of various nickel minerals and solution species indicates that nickel ferrite is the solid species that will most likely precipitate in soils (Sadiq and Enfield 1984a). Experiments on 21 mineral soils supported its formation in soil suspensions following nickel adsorption (Sadiq and Enfield 1984b). The formation of nickel aluminate, phosphate, or silicate was not significant. Ni and Ni(OHX are major components of the soil solution in alkaline soils. In acid soils, the predominant solution species will probably be NE, NiS04°, and NiHP04° (Sadiq and Enfield 1984a). 

In a similar manner, uniform spherical particles of nickel ferrite (NiFe204) (6), cobalt ferrite (CoFe204) (7), and cobalt-nickel ferrite (CorNi vFe204) (8) were prepared as well. 

Person 2 Calculate the net magnetic moment per unit cell for nickel ferrite. Remember that there is more than one formula unit (NiFc204) per unit ceU in the inverse spinel structure. 

Person 1 Calculate the saturation magnetization, Ms, for nickel ferrite, which has a lattice parameter of a = 0.833 nm. 

The addition of cobalt to a nickel ferrite has been employed to increase resistivity, as illustrated in Fig. 9.24. For an explanation it is necessary to consider the third ionization potentials of chromium, iron, manganese, cobalt and nickel, which increase in this order. The addition of cobalt tends to maintain the iron in the Fe3+ state by virtue of the equilibrium... 

Nickel ferrite, Ni(Fe02)2, is obtained on addition of potassium hydroxide to a mixed solution of a nickel salt and ferric chloride,2 and igniting. It is a brown substance, strongly magnetic. 

These results demonstrate tliat shock-wave synthesis is a novel metliod to prepare nanosized materials with some unique physical and chemical properties. In the light of the experimental results, nanosized zinc ferrite and nickel ferrite synthesized by shock-wave treatment may Iiave potential applications as magnetic materials and photocatalysts. 

Figure 6.2. Curves of magnetization for shock synthesized nickel ferrites and the precursor material, (a) Co-precipitated mixture of nickel oxide and ferric oxide (b) nickel ferrite synthesized by calcination (c,d) nickel ferrite synthesized by shock waves of 27.6 GPa and 23.4 GPa, respectively.

As concerns the piezoelectric layer, the first choice often goes to lead zirconate titanate (PZT) because of its outstanding piezoelectric, pyroelectric and ferroelectric properties. Nickel ferrite (NF) is not widely employed for the synthesis of the multilayered composites owing to a strong reduction of its magnetization in the lower grain size limit. However, a very thin NF layer can help to attain entirely different properties and, hence, this material has been chosen as a sandwiched layer in the present work. 

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