Copper gold structure

The structure of alloys and structural changes at certain temperatures can explain the memory effect of special alloys (see E5.6) like Nitinol , a nickel-titanium alloy [4]. The structure as well as the much greater electric conductivity explains the difference between the copper-gold structures (CuAu and Cu3Au) and... 

Many alloys are substitutional solid solutions, well-studied examples being copper-gold and copper-nickel. In both of these examples, the alloy has the same crystal structure as both parent phases, and the metal atoms simply substitute at random over the available metal atom sites (Fig. 4.4a). The species considered to be the defect is clearly dependent upon which atoms are in the minority. 

A well researched and popular class of monolayers is based on the strong adsorption of thiols (R - SH), disulfides (R - S - S - R) and sulfides (R - S - R) onto metal surfaces. Although thiols, disulfides, and sulfides strongly align with a number of different metals Hke gold, silver, platinum, or copper, gold is usually the substrate of choice because of its inert properties and the formation of a well-defined crystal structure. 

Ordering lowers the electrical resistivity of copper-gold alloys. Adapted from C. S. Barrett, Structure of Metals and Alloys (New York McGraw-Hill, 1943), p. 244, figure 14. 

Just as the body-centered cubic structure can be considered as made of two interpenetrating simple cubic lattices, the face-centered cubic structure can be made of four simple cubic lattices. There are some interesting cases of ordered alloys with this crystal structure and ratios of approximately one to three of the two components. An example is found in the copper-gold system, where such a phase is found in the neighbor-... 

Corrosion by dealloying is common in brasses here the zinc component of the alloy is preferentially removed. Brasses with high proportions of the P phase are especially prone to this type of attack. The mechanism appears to be corrosion of both copper and zinc from the metal the zinc passes into solution but the copper is re-deposited with a porous structure of low strength. Aluminium bronzes also suffer dealloying of the aluminium component if incorrectly heat treated. Other metals which may be preferentially dissolved from their alloys are manganese from copper-manganese, nickel from copper-nickel, copper from either copper-silver or copper-gold, and tin from tin-lead (solders). It is evident from this list that it is the component which is anodic to the alloy which is removed. 

The conductivity of an electrolytic solution decreases as the temperature falls due to the decrease in viscosity which inhibits ionic mobility. The mobility of the electron fluid in metals is practically unaffected by temperature, but metals do suffer a slight conductivity decrease (opposite to ionic solutions) as the temperature rises this happens because the more vigorous thermal motions of the kernel ions disrupts the uniform lattice structure that is required for free motion of the electrons within the crystal. Silver is the most conductive metal, followed by copper, gold, and aluminum. 

Hih K. C., Kendrick R. D., Crowhurst P. V., and Gow P. (2002) Copper-gold mineralisation in New Guinea tectonics, lineaments, thermochronology and structure. Austral. 

Among relevant studies one can cite the investigations of sulfur adsorption on molybdenum " ), silicon ), copper " ), gold ), vanadium ) and iron " ). Such examples may be found in very large number in the literature we shall try and set in evidence the general trends observed in structures resulting from sulfur adsorption on metallic surfaces. 

Not all materials are so well behaved. For example, many metal alloys have considerable composition ranges and a correct calculation of the intensities of diffracted beams needs inclusion of a site occupancy factor. For example, the disordered gold-copper alloy Au Cu, is able to take compositions with x varying from 1, pure gold, to 0, pure copper. The structure of the alloy is the copper (Al) structure, (see Chapter 1), but in the alloy the sites occupied by the metal atoms contain a mixture of Cu and Au, (Figure 8.1). This situation can be described by giving a site occupancy factor to each type of atom. For example,... 

Figure 8.7 The structure of ordered copper - gold alloys (a) CuAu II (b) CuAu I...

A typical example of an alloy of this class, and one which has been extensively investigated, is the system copper-gold. These two metals are chemically closely related, have a similar electronic configuration and have the same crystal structure. The atomic radii are not very different, being 1 28 and 1 44 A, respectively. 

The intermediate phases found in alloys of two true metals have a number of different structures, but many of these are common to more than one system. In addition to the phases already considered in the copper-gold and iron-aluminium systems we shall describe two, one because of its common occurrence and one because of its geometrical interest. 

A copper-gold alloy has a cubic structure. The atom positions are ... 

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