Phase copper/silver

Fig. 2. Liquidus of isotherms of gold-copper-silver alloys and phase diagrams of the binary constituents (83).

Fig. A 1.34. Dendrites of silver in a copper-silver eutectic matrix, x330. (After G. A. Chadwick, Metallography of Phase Transformations, Butterworth, 1972.)...

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 group Ib elements—copper, silver, and gold—stand in contradistinction to elements such as rubidium and vanadium. These metals are rather electronegative and soft, and prefer two-coordinate directional bonding. These characteristics are not conducive to the incorporation of these elements into rock-forming oxide matrices, and they therefore form their own minerals, occur in the native state, or reside in trace sulfides in the cmst. They also partition readily into fluid phases, promoting their redistribution in the crust, and the formation of ores. 

Liquid-phase selective oxidations are normally catalysed homogeneously. A small but significant interest has recently arisen in the use of solid catalysts for liquid-phase oxidation, particularly of alkyl aromatics. Shalya et al. have compared the activity of copper, silver, and gold metals as catalysts for cumene oxidation (Table 2). Silver was found to combine good selectivity for the desired product, cumene hydroperoxide, with an activity similar to that of copper. With supported catalysts, silver is considerably more active than copper, while gold is totally inactive. 

Noble metals - copper, silver and gold - are monovalent elements with a /cc-like crystallographic structure in the bulk phase under normal conditions. Their dielectric function has been the subject of various experimental investigations in the past [1-6]. A compilation and an analyse of the main results can be found in [7]. The response of noble metals to an electromagnetic excitation in the UV-visible range cannot be described, contrarily to the case of alkalis, by the only behaviour of the quasi-free conduction electrons (sp band), but must include the Influence of the bound electrons of the so-called d bands [8]. Hence, the total dielectric function of noble metals can be written as the sum of two contributions, one due to electronic transitions within the conduction band (intraband transitions) and the other stemming from transitions from the d bands to the conduction one (Interband... 

With respect to the phase diagram of the copper-silver system (Figure 8.28) ... 

Figure 8 (a) Charging of bare metal clusters (Equation (28)) in water, dichloromethane, and alkane solvents, (b) Experimental data for copper clusters in the gas phase and silver clusters in water. ... 

There are also three two-phase regions found for the copper-silver system (Figure 9.7) a + L, j3 + L, and a+ j3- The a- and j8-phase solid solutions coexist for all compositions and temperatures within the a+ j3 phase field the a + liquid and (3 + liquid phases also coexist in their respective phase regions. Furthermore, compositions and relative amounts for the phases may be determined using tie lines and the lever rule as outlined previously. 

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