Alloys crystalline structure

The properties of alloys are affected by their composition and structure. Not only is the crystalline structure important, but the size and texture of the individual grains also contribute to the properties of an alloy. Some metal alloys are one-phase homogeneous solutions. Examples are brass, bronze, and the gold coinage alloys. Other alloys are heterogeneous mixtures of different crystalline phases, such as tin-lead solder and the mercury-silver amalgams used to fill teeth. 

To evaluate the catalytic activity or to investigate the reaction mechanism, planar electrodes with well-defined characteristics such as surface area, surface and bulk compositions, and crystalline structure have often been examined in acidic electrolyte solutions. An appreciable improvement in CO tolerance has been found at Pt with adatoms such as Ru, Sn, and As [Watanabe and Motoo, 1975a, 1976 Motoo and Watanabe, 1980 Motoo et al., 1980 Watanabe et al., 1985], Pt-based alloys Pt-M (M = Ru, Rh, Os, Sn, etc.) [Ross et al., 1975a, b Gasteiger et al., 1994, 1995 Grgur et al., 1997 Ley et al., 1997 Mukeijee et al., 2004], and Pt with oxides (RuO cHy) [Gonzalez and Ticianelli, 2005 Sughnoto et al., 2006]. 

The selection of materials for high-temperature applications is discussed by Day (1979). At low temperatures, less than 10°C, metals that are normally ductile can fail in a brittle manner. Serious disasters have occurred through the failure of welded carbon steel vessels at low temperatures. The phenomenon of brittle failure is associated with the crystalline structure of metals. Metals with a body-centred-cubic (bcc) lattice are more liable to brittle failure than those with a face-centred-cubic (fee) or hexagonal lattice. For low-temperature equipment, such as cryogenic plant and liquefied-gas storages, austenitic stainless steel (fee) or aluminium alloys (hex) should be specified see Wigley (1978). 

The main considerations of mechanical properties of metals and alloys at low temperatures taken into account for safety reasons are the transition from ductile-to-brittle behavior, certain unconventional modes of plastic deformation, and mechanical and elastic properties changes due to phase transformations in the crystalline structure. 

J.W. Klement, R.H. WiUens, P. Duwez, Non-crystalline structure in solidified gold-silicon alloys, Nature 187 (1960) 869-870. 

Metallic Glasses. Under highly specialized conditions, the crystalline structure of some metals and alloys can be suppressed and they form glasses. These amorphous metals can be made from transition-metal alloys, eg, nickel—zirconium, or transition or noble metals in combination with metalloid elements, eg, alloys of palladium and silicon or alloys of iron, phosphoms, and carbon. 

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],... 

When a small amount of an element is added to a metal and the original metal crystalline structure remains the same, this alloy is called a metal solution. 

When we determined the crystalline structure of solids in Chapter 4, we noted that most transitional metals form crystals with atoms in a close-packed hexagonal structure, face-centered cubic structure, or body-centered cubic arrangement. In the body-centered cubic structure, the spheres take up almost as much space as in the close-packed hexagonal structure. Many of the metals used to make alloys used for jewelry, such as nickel, copper, zinc, silver, gold, platinum, and lead, have face-centered cubic crystalline structures. Perhaps their similar crystalline structures promote an ease in forming alloys. In sterling silver, an atom of copper can fit nicely beside an atom of silver in the crystalline structure. 

These catalysts are composed of one or several metallic active components, deposited on a high surface area support, whose purpose is the dispersion of the catalytically active component or components and their stabilization [23-27], The most important metallic catalysts are transition metals, since they possess a relatively high reactivity, exhibit different oxidation states, and have different crystalline structures. In this regard, highly dispersed transition clusters of metals, such as Fe, Ru, Pt, Pd, Ni, Ag, Cu, W, Mn, and Cr and some alloys, and intermetallic compounds, such as Pt-Ir, Pt-Re, and Pt-Sn, normally dispersed on high surface area supports are applied as catalysts. 

Peculiarity of the fullerene molecule formation also reveals itself in a fullerite crystal structure. Cubic crystal lattices of fullerites and hydrofullerites behave like those of different metals and alloys. Fullerene molecules are distributed in the lattice sites while atoms of elements are distributed in the octa- and tetrahedral interstitial sites forming the interstitial solid solutions. Fullerene molecules substitute each other in the sites of lattice and form the substitution solid solutions. Forming exo- and endocompounds, fullerene molecules that are in the lattice sites can change considerably the properties of crystal, whereas its crystalline structure remain unchanged. 

In addition to the opportunities for new materials synthesis and characterization along these lines, transport properties, rheology, and processing techniques for liquid crystal polymers are essentially unexplored. Experiences with synthesis of polymer structure based on these liquid crystal templates may open up other creative avenues for template synthesis, for example, inside other crystalline structures, chlathrates, or zeolites, or on surfaces [4], Composites, alloys, or mixtures of liquid crystalline and flexible polymers may produce new materials. 

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