Amorphous alloys structure

Since amorphous alloys can be regarded as metallic solids with a frozen-in melt structure, the liquid structure freezes at different temperatures... 

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... 

In amorphous solids there is a considerable disorder and it is impossible to give a description of their structure comparable to that applicable to crystals. In a crystal indeed the identification of all the atoms in the unit cell, at least in principle, is possible with a precise determination of their coordinates. For a glass, only a statistical description may be obtained to this end different experimental techniques are useful and often complementary to each other. Especially important are the methods based on diffraction experiments only these will be briefly mentioned here. The diffraction pattern of an amorphous alloy does not show sharp diffraction peaks as for crystalline materials but only a few broadened peaks. Much more limited information can thus be extracted and only a statistical description of the structure may be obtained. The so-called radial distribution function is defined as ... 

Metal alloys can be amorphous, too. LiquidmetaF alloy is an amorphous alloy of zirconium mixed with nickel, titanium, copper, and beryllium. It is used in the heads of some brands of golf clubs. Traditional metal club heads may have microscopic gaps where planes of metallic crystals meet. These tiny gaps are a potential source of weakness. The amorphous alloy is non-crystalline, so the metal structure does not have potential breakage sites. 

RELATION BETWEEN MAGNETIC PROPERTIES AND THE STRUCTURE OF IRON-BASED AMORPHOUS ALLOYS DETERMINED BY ELECTRON DIFFRACTION... 

Amorphous alloys are characterised by a structural disorder where each atom constitutes a structural unit. In this state, the low mass density and the loss of the periodicity enhance the localisation of the 3d electrons in the rare earth-transition metal alloys. In... 

Ion implantation (qv) has a large (1014 K/s) effective quench rate (64). This surface treatment technique allows a wide variety of atomic species to be introduced into the surface. Sputtering and evaporation methods are other very slow approaches to making amorphous films, atom by atom. The processes involve deposition of a vapor onto a cold substrate. The buildup rate (20 tm/h) is also sensitive to deposition conditions, including the presence of impurity atoms which can facilitate the formation of an amorphous structure. An approach used for metal—metalloid amorphous alloys is chemical deposition and electro deposition. 

Many amorphous alloys were tested in the hydrogenation of ethylene. It was shown that the thermal pretreatment of a Cu7oZr3o amorphous precursor in hydrogen leads to structural modification and the resulting catalysts exhibit extremely high activities in ethylene hydrogenation197 (Table 10). 

Surface characterization includes also the study of the modification of a surface under cathodic load or after some pretreatments. The presence of residual surface oxides can explain some observations otherwise inexplicable. Activation in situ usually results in composite structures which are difficult to identify by X-ray, and may contain metallic and non-metallic components. Particularly crucial is the case of the surface structure of glassy metals or amorphous alloys. 

Several materials have been investigated as cathode activators. Among the most studied systems we find CuTi, CuZr, NiTi, NiZr, FeCo, NiCo. A variety of methods are available to prepare amorphous alloys [562] and, as expected, the resulting activity is largely dependent on them. Normally, amorphous phases are obtained by rapidly quenching a melt. The material can thus be obtained in the form of ribbons, but mechanical alloying by compaction is also possible [572]. The metallic components are usually alloyed with non-metallic components such as B, Si and P which stabilize the metastable non-crystalline structures. Electrodeposition is thus also a viable preparation route [573, 574],... 

Figure 5. Schematic arrangement of the surface of a partly crystallized E-L TM amorphous alloy such as Pd-Zr. A matrix of zirconia consisting of the two polymorphs holds particles of the L transition metal (Pd) which are structured in a skin of solid solution with oxygen (white) and a nucleus of pure metal (black). The arrows indicate transport pathways for activated oxygen either through bulk diffusion or via the top surface. An intimate contact with a large metal-to-oxide interface volume with ill-defined defective crystal structures (shaded area) is essential for the good catalytic performance. The figure is compiled from the experimental data in the literature [26, 27].

Most relevant for the oxygen transport should be the defective crystal structure of both catalyst components. The defective structure and the intimate contact of crystallites of the various phases are direct consequences of the fusion of the catalyst precursor and are features which are inaccessible by conventional wet chemical methods of preparation. Possible alternative strategies for the controlled synthesis of such designed interfaces may be provided by modem chemical vapor deposition (CVD) methods with, however, considerably more chemical control than is required for the fusion of an amorphous alloy. 

The total density of states (DOS) are obtained by summing of the partial DOS for the atoms in the central part of the structure models in order to reproduce the electronic structure of the bulk alloys as appropriately as possible. The number of the sampled atoms for the calculation of the amorphous alloys is typically 6 for one element. In case of crystals, a few atoms are sampled for calculation. 

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