Copper phase

The lead—copper phase diagram (1) is shown in Figure 9. Copper is an alloying element as well as an impurity in lead. The lead—copper system has a eutectic point at 0.06% copper and 326°C. In lead refining, the copper content can thus be reduced to about 0.08% merely by cooling. Further refining requites chemical treatment. The solubiUty of copper in lead decreases to about 0.005% at 0°C. 

Fig. 14. Aluminum-rich portion of alurninum—copper-phase diagram.

With binary copper—lead, the continuous copper phase provides the primary load support while pockets of 20—50% lead supply a continuous lead surface film. Tin content of 3—5% is commonly incorporated with the lead to minimi2e corrosion. Copper—lead alloys, either cast or sintered on a steel back, provide good fatigue resistance for heavy-duty main and connecting rod bearings for auto, tmck, diesel, and aircraft engines. 

The aluminium-copper phase diagram is shown below. 

Fig. 20.41 (a) Silver-copper phase. diagram and (b) magnesium-tin phase diagram... 

Fig. 20.43 Aluminium-rich end of the aluminium-copper phase diagram...

Fig. 24. STM image of a thick Cu overlayer on Au(100) in 0.05 M H2S04 + 1 mM CuS04 at —0.2 V vs. SCE. Clusters have been formed on top of the wavy copper phase, the latter still being clearly visible in between the clusters [78],...

The crystal structures of a handful of ternary anhydrous selenites are known, and NaLa(Se03)2 and NaY(Se03)2,230 containing additional Na+ ions, the copper phases M2Cu(Se03)4 (M=La-Tb)231,232 and the lithium selenite Li3-Lu5(Se03)9233 should be mentioned. The copper selenites show the M3+ ions in... 

Some of the results obtained by Ben-Taarit et al. for propylene oxidation on Cu2+Y are similar to those reported by Mochida et al. when an excess of propylene is used in the feed [2]. The former authors stress that under these circumstances Cu+2 in Cu +Y is transformed to a Cu°/Cu20/Cu0 mixture. However, using optimized 02/propylene ratios, flow rates and temperatures, it seems that 70% selectivity for acrolein at 50% propylene conversion is achievable. Under those conditions there was no evidence for the formation of either a metallic or an oxide copper phase [2]. 

In the particular cell (Fig. 6.28) generated by the measuring process, it will be only as a special case that the metal Mj (of the electrode/electrolyte interface under study) is identical with the metal M2 (the connecting wires of the measuring instrument). In general, M, and M2 will be different metals, say, platinum and copper. The meeting of the platinum and copper phases produces another double layer and an... 

Propene to acrolein. Hildenbrand and Lintz87,88 have used solid electrolyte potentiometry to study the effect of the phase composition of a copper oxide catalyst on the selectivity and yield of acrolein during the partial oxidation of propene in the temperature range of 420-510°C. Potentiometric techniques were used to determine the catalyst oxygen activity, and hence the stable copper phase, under working conditions. Hildenbrand and Lintz used kinetic measurements to confirm that the thermodynamically stable phase had been formed (it is known that propene is totally oxidised over CuO but partially oxidised over ). 

The results of Hildenbrand and Lintz showed good quantitative agreement with previous kinetic work of Riekert and Greger.84,85,89 Reaction rate measurements were indicative of which copper phase was present this phase corresponding to the thermodynamically favoured phase. Furthermore, hysteresis observed in the reaction rate data was also observed in the oxygen activity measurements as in other SEP work on oxides.35,86... 

The silver-copper phase diagram. Reprinted with permission of ASM International from L. A. Willey, Metals Handbook, vol. 8, 8th ed. (Materials Park, OH ASM, 1973), p. 259. All rights reserved, www.asminternational.org. 

Figure 8 shows X-ray diffraction (XRD) patterns of bismuth nanowire arrays (Lin et al., 2000b). It illustrates that the crystal structure of bismuth nanowires is the same as that of bulk bismuth and that no copper phases were present. The nanowires have a preferred wire orientation dependent on their diameters. The major orientations of the 95-nm and 40-nm bismuth nanowire arrays were normal to the (202) and (012) lattice planes, respectively, indicating that most (> 80%) of the nanowires were oriented along the [1011] and [0112] directions for <7W > 60 nm and <7W < 50 nm, respectively (Zhang et al., 1999 Lin et al., 2000b). The existence of more than one dominant orientation in the 52-nm Bi nanowires (Fig. 8(b)) was... 

A second problem with surface inhomogeneities in metals is the depletion of a more chemically active phase in contact with a less chemically active phase. When two metallic phases are in electrical contact, the more chemically active phase of the alloy corrodes much more rapidly than normal, even when it is exposed to even a mildly corrosive environment. If a coin has two phases exposed at the surface, such as copper and lead, then the more active metal, namely lead, will corrode preferentially. However, corrosion stops locally as soon as a given lead particle is consumed. The copper matrix then prevents further corrosion of lead because the copper phase must first corrode before additional lead is exposed at the surface. Hence,... 

The dependence of the activity of catalysts on their copper content can be seen on Fig. 4. (12). For all the four reactants the activity passes through a maximum the interpretation of which requires at least two factors of opposite effect. The initial increase in activity is caused presumably by the increasing dispersion, although the change in electronic structure (ligand effect) may also play a role in it. With increasing copper content the proportion of copper-rich and pure copper phases increases on the surface, and therefore the activity rapidly decreases from ca. 40 at% of Cu and the 80 at% Cu/Pd catalyst is, in accordance with the potentiodynamic investigations inactive. 

The present monograph was first written as a chapter for Volume 8 of the series Materials Sdence and Technology A Comprehensive Treatment , edited by Robert W. Cahn, Peter Haasen, and Edward J. Kramer (Volume Editor Dr. Karl Heinz Matucha). Its aim is to give an overview of intermetallics, which is both detailed and comprehensive and which includes the fundamentals as well as applications. The result is an extended, critical review of the whole field of intermetallics with an emphasis on those intermetallic phases which have already been applied as functional or structural materials or which are currently the subject of materials developments. A historical introduction and a discussion of the relationship between atomic bonding, crystal structure, phase stability and properties is followed by a discussion of the major classes of intermetallics. The titanium aluminides, nickel aluminides, iron aluminides, copper phases, A15 phases. Laves phases, beryllides, rare earth phases, and siliddes are reviewed. In particular, the crystal structures, phase diagrams, and physical properties as well as the mechanical and corrosion behavior are treated. The state of developments as well as prospects and problems are discussed in view of present and future applications. The publisher has decided to publish the review as a separate monograph in order to make it accessible to a wider audience. 

The chanistry of copper in water and soils is very complex. Potential chemical forms include insoluble organic complexes, sulfide minerals, and solid copper phases. It is clear that changes in soil redox condition (from oxidized to reduced) change the relative distribution of copper in various soil phases. 

Fewer EXAFS works have been devoted to the study of catalytic systems under reaction conditions due, as already said, to inherent limitations of the technique at high, working temperatures characteristic of catalytic reactions. Among these, a majority include studies of Cu/ZnO (Cu/Si02) in methanol synthesis.The solid state physics of the active copper phase in methanol synthesis is a rather intriguing problem which has not achieved consensus concerning the oxidation state and the hosting of the Cu phase characteristics. The EXAFS works mentioned above elucidated mainly the importance of the metallic state in the reaction. Similarly, the metallic state has been shown to be of importance in the water gas shift reaction (WGS) in Cu, Au, and bimetallic Pd-Cu systems supported on ceria. The importance of ceria vacancies on the activation of water and of the metal (and more precisely, of the metal at support boundaries) for CO activation appear as key elements for this reaction. The bimetallic Pd-Cu work analyses the modulation of Pd behaviour by effect of the alloy with the base... 

A large variety of catalysts for the steam reforming of methanol which include copper in their composition have been reported. " Commercial Cu/ZnO water-gas shift and methanol synthesis catalysts - have also been found to be active for the steam reforming reaction. Microstructural characteristics of the copper phase in Cu/ZnO catalysts depended on the aging time of the precipitate, resulting in changes in reducibility and crystallite size which produced an increase in the catalytic activity. Moreover,... 

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