Amorphous intermetallic

For the spectra of Ni, peaks corresponding to Ni oxide and Ni metal are observed in the as-prepared sample [28-30]. After the etching with Ar, however, the peak of Ni metal is predominant. This implies that the state of Ni in the Ni-Zn nanoclusters is metallic, although their surface was oxidized under the atmospheric conditions. On the other hand, the identification of Zn state is difficult because the peak positions of Zn and ZnO in ESCA spectra are very close to each other. Furthermore, the B/Ni ratio determined by ESCA was increased with increasing Zn added e.g., Ni B = 73.3 26.7 and 60.6 39.4 for Zn/Ni = 0.0 and 1.0, respectively. Because no crystalline structure was found except for Ti02 from both electron and X-ray diffraction patterns of the respective samples, it can be concluded that formed nanoclusters were amorphous. Ni-Zn nanoclusters would be composed of amorphous intermetallic compounds through the... 

In order to describe the magnetic order behavior of amorphous intermetallic compounds containing rare-earth atoms with nonzero orbital momentum, such as a-TbFe2, Harris et al. (1973) have introduced the random anisotropy-axis ... 

Oranges, citric acid in, 6 632t ORBIT PRINT SELECT software, 18 243 Orbitrap, 15 662-663 Orb web, structure of, 22 630 Ordered intermetallic alloys, 13 530 Order, in amorphous semiconductor structure, 22 128-129 Ordering, in ternary semiconductor alloy preparation, 22 158-159 Order of addition, in large-scale... 

The precursor alloy is quenched to form small grains readily attacked by the caustic solution [31], Quenching can also enable specific intermetallic phases to be obtained, although this is less common. Yamauchi et al. [32-34] have employed a very fast quench to obtain a supersaturation of promoter species in the alloy. It is even possible to obtain an amorphous metal glass of an alloy, and Deng et al. [35] provide a review of this area, particularly with Ni, Ni-P, Ni-B, Ni-Co, and Ni-Co-B systems. The increased catalytic activity observed with these leached amorphous alloy systems can be attributed to either chemical promotion of the catalyzed reaction or an increased surface area of the leached catalyst, depending on the components present in the original alloy. Promotion with additives is considered in more detail later. 

Another characteristic point is the special attention that in intermetallic science, as in several fields of chemistry, needs to be dedicated to the structural aspects and to the description of the phases. The structure of intermetallic alloys in their different states, liquid, amorphous (glassy), quasi-crystalline and fully, three-dimensionally (3D) periodic crystalline are closely related to the different properties shown by these substances. Two chapters are therefore dedicated to selected aspects of intermetallic structural chemistry. Particular attention is dedicated to the solid state, in which a very large variety of properties and structures can be found. Solid intermetallic phases, generally non-molecular by nature, are characterized by their 3D crystal (or quasicrystal) structure. A great many crystal structures (often complex or very complex) have been elucidated, and intermetallic crystallochemistry is a fundamental topic of reference. A great number of papers have been published containing results obtained by powder and single crystal X-ray diffractometry and by neutron and electron diffraction methods. A characteristic nomenclature and several symbols and representations have been developed for the description, classification and identification of these phases. 

General characteristics of alloys such as those presented in Fig. 3.3 have been discussed by Fassler and Hoffmann (1999) in a paper dedicated to valence compounds at the border of intermetallics (alkali and alkaline earth metal stannides and plumbides) . Examples showing gradual transition from valence compounds to intermetallic phases and new possibilities for structural mechanisms and bonding for Sn and Pb have been discussed. Structural relationships with Zintl phases (see Chapter 4) containing discrete and linked polyhedra have been considered. See 3.12 for a few remarks on the relationships between liquid and amorphous glassy alloys. 

Structural relations between quasicrystals and other intermetallic phases. As discussed in several sections of the review published by Kelton (1995) on quasicrystals and related structures, numerous studies and observations indicate structural similarities between non-periodic quasicrystal phases with crystalline phases and also, on the other hand, with amorphous, glassy and liquid phases. 

X.L. Yeh, K. Samwer, W.L. Johnson, Formation of an amorphous metallic hydride by reaction of hydrogen with crystalline intermetallic compounds - a new method of synthesizing metallic glasses, Appl. Phys. Lett. 42 (1983) 242-244. 

The second type of impurity, substitution of a lattice atom with an impurity atom, allows us to enter the world of alloys and intermetallics. Let us diverge slightly for a moment to discuss how control of substitutional impurities can lead to some useful materials, and then we will conclude our description of point defects. An alloy, by definition, is a metallic solid or liquid formed from an intimate combination of two or more elements. By intimate combination, we mean either a liquid or solid solution. In the instance where the solid is crystalline, some of the impurity atoms, usually defined as the minority constituent, occupy sites in the lattice that would normally be occupied by the majority constituent. Alloys need not be crystalline, however. If a liquid alloy is quenched rapidly enough, an amorphous metal can result. The solid material is still an alloy, since the elements are in intimate combination, but there is no crystalline order and hence no substitutional impurities. To aid in our description of substitutional impurities, we will limit the current description to crystalline alloys, but keep in mind that amorphous alloys exist as well. 

D.E. Luzzi, M. Meshii, The crystalline to amorphous transition of intermetallic compounds under electron irradiation -a review, Res. Mechanica 21(3) (1987) 207-247. 

R.A. Varin, T. Czujko, J. Mizera, The effect of MgNi2 intermetallic compound on nanostructurization and amorphization of Mg-Ni alloys processed by controlled mechanical milling ,... 

---