Hexagonally close packed nickel

Stereochemistry of Monohydrido- and Dihydrido-Dodecanickel Carbonyl Clusters Containing a Hexagonal Close Packed Nickel Fragment... 

Hexagonal close-packed 6 6 MO All oct. Nickel arsenide NiAs, FeS, FeSe, CoSe... 

The nickel arsenide structure is the equivalent of the sodium chloride structure in hexagonal close-packing. It can be described as an hep array of arsenic atoms with nickel atoms occupying the octahedral holes. The geometry about the nickel atoms is thus octahedral. This is not the case for arsenic each arsenic atom sits in the centre of a trigonal prism of six nickel atoms (Figure 1.36). 

A few short papers have dealt with the zero-field NMR of small ferromagnetic nickel and cobalt particles. The physical basis of such measurements is more complicated than that of NMR in an applied field, and this is not discussed here. Suffice it to say that for Ni a considerable size-dependent line broadening is found (189), which could possibly be used to investigate the effect of chemisorption on the surface magnetism of such particles. The Co zero-field NMR can distinguish between superparamagnetic, FCC, and hexagonal close packed (HCP) cobalt (190). 

Nickel Arsenide (Hexagonal Close Packed, Octahedral Holes Fully Occupied)... 

The crystal structures of metallic ruthenium and copper are different, ruthenium having a hexagonal close-packed structure and copper a face-centered cubic structure (7). Although the ruthenium-copper system can hardly be considered one which forms alloys, bimetallic ruthenium-copper aggregates can be prepared that are similar in their catalytic behavior to alloys such as nickel-copper (3,4,8). 

A closely analogous state of affairs is seen in the systems NiTe2-NiTe and TiTe2-TiTe, in which the AB2 compound has the cadmium iodide structure and the AB compound that of nickel arsenide. In both of these structures the B atoms are arranged as in hexagonal close-packing, but in other respects the relationship between them is precisely the same as that between the cadmium chloride and sodium chloride structures, so that solid solution can take place by the same mechanism. Examples such as this, and many others which could be quoted, emphasize that solid solution is in no sense a satisfactory criterion for isomorphism, and that substances may form solid solution even if their structures are formally quite different. 

Many T2-B2 systems, at the appropriate composition, display either the nickel arsenide structure or one geometrically closely related to it. This structure has already been described ( 8.12 and fig. 8.02) and it will be remembered that it is characterized by the asymmetry of the co-ordination each of the more metallic T atoms is octahedrally coordinated by six atoms B of the less metallic component, whereas each B atom is surrounded by six neighbours T at the corners of a trigonal prism. For our present purposes, however, it is convenient to describe the structure in somewhat different terms, for it can alternatively be regarded as an expanded hexagonal close-packed array of B atoms with the T atoms disposed in its octahedral interstices. This interstitial picture explains the wide range of composition over which the structure... 

The metal has a hexagonal close-packed lattice and resembles other transition metals such as iron and nickel in being hard, refractory (m.p. 1680°+10°, b.p. 3260°), and a good conductor of heat and electricity. It is, however, quite light in comparison to other metals of similar mechanical and thermal properties and unusually resistant to certain kinds of corrosion and has therefore come into demand for special applications in turbine engines and industrial chemical, aircraft, and marine equipment. 

Wurtzite, nickel arsenide, cadmium iodide, corundum, illmenite, and olivine are all structures in which the anion arrangement is HCP. For example, in corundum (AI2O3) the oxygen ions are hexagonally close-packed, and the A1 ions fill two-thirds of the available octahedral sites. In contrast, if one-half the tetrahedral sites are filled, the resulting structure is wurtzite (Fig. 3Ad). 

Plasmochemical synthesis of carbon nanotubes was carried out at 500-700 °C in the barrier-discharge reactor with two coaxial electrodes between which the pulsed voltage (10 kV, 25 kHz) was applied. As the synthetic reaction, the disproportion of carbon monoxide was used. All experiments were performed at atmospheric pressure. Nickel-modified hexagonal close-packed nanochannel alumina templates were fabricated by anodization of aluminum with subsequent... 

The alloy nickel arsenide has a structure in which all of the arsenic atoms are in a hexagonal close-packed array and the nickel atoms occupy all of the octahedral positions the formula of nickel arsenide is ... 

At temperatures up to 417°C, cobalt has a hexagonal close packed (hep) structure, whereas above 417°C, it is face-centered cubic (fee). Alloying elements that are fee stabilizers (such as nickel, iron, and carbon) lower the transformation... 

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