Cu-Co System

The Cu-Co system is a particularly simple precipitation system in which a Corich /3 phase precipitates in a Cu-rich terminal a phase. The f.c.c. lattices of both phases are well matched in three dimensions, so that the precipitate interfaces are coherent with respect to either lattice as a reference structure and the interfacial energy is sufficiently isotropic so that they are almost spherical, as in Fig. 19.2. Both the interfacial energy and strain energy are therefore relatively low and the nucleation of the f3 phase is therefore relatively easy and occurs homogeneously. This system has been used to test the applicability of the classical nucleation theory (Section 19.1.1) [11, 12]. In this work, the experimental conditions under which 

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The multilayered Cu/Co systems discussed here can be grown as described next (6b). Electrolyte composition is based on a cobalt/copper ratio of 100 1 and consists of a solution of 0.34 M cobalt sulfate, 0.003 M copper sulfate, and 30g/L boric acid. The pH is fixed around 3.0, and there is no forced convection while deposition is carried out. The electrodeposition may usually be carried out potentiostatically at 45°C between —1.40 V versus SCE for the cobalt and —0.65 V versus SCE for the copper with an 3 cell potential interrupt between the cobalt-to-copper transition to avoid cobalt dissolution, which can occur when there is no interrupt. 

Ant] Antoni-Zdziobek, A., Colinet, C., CVM Calculations of Phase Equilibria in the Fe-Cu-Co System Including Both Chemical and Magnetic Interactions , Proc. Disc. Meet. Thermodyn. Alloys, 35 (2000) (Phase Relations, Thermodyn., 0)... 

Although the energy decompositions discussed so far provide a rather detailed understanding of the interaction of adsorbates with clusters, it remains an open question how accurately the cluster calculations mimick chemisorption. Among the many studies of the effect of cluster size, there are two on the Cu /CO system which used energy decomposition to consider the variation of the various energy contributions with cluster size and shape (Post and Baerends [26], and Hermann, Bagus, Nelin [84]. 

The site specificity of reaction can also be a state-dependent site specificity, that is, molecules incident in different quantum states react more readily at different sites. This has recently been demonstrated by Kroes and co-workers for the Fl2/Cu(100) system [66]. Additionally, we can find reactivity dominated by certain sites, while inelastic collisions leading to changes in the rotational or vibrational states of the scattering molecules occur primarily at other sites. This spatial separation of the active site according to the change of state occurring (dissociation, vibrational excitation etc) is a very surface specific phenomenon. 

Figure 10 presents the Curie temperature (T ) vs the TM-content (x) for Co- and Fe-based biaary alloys. Alloying rare-earth elements with small amounts of transition metals (x < 0.2) leads to a decrease ia Curie temperature. This is particularly obvious ia the Gd—Co system where it corresponds to a nonmagnetic dilution similar to that of Cu (41,42). This iadicates that TM atoms experience no exchange coupling unless they are surrounded by a minimum number j of other TM atoms. The critical number is j = 5 for Fe and j = 7 for Co. The steep iacrease of for Co-based alloys with x about 0.7 is based on this effect. 

At this point, it seems appropriate to consider the Co-, Ni-, and Cu-ethylene system as a whole, both to rationalize any spectral trends as a function of metal, and to evaluate the use of these complexes as local-ized-bonding models for chemisorption of C2H4. 

SO2 nearly completely deactivated the Cu-ZSM-5, resulted in an inhibition for Co-ZSM-5 and an enlargement of the N2O conversion over Fe-ZSM-5 (figure 9). Both the Fe and the Co systems returned to their original activity after removal of the SO2, this took several hours. 

The Cu-, Co- and Fe-ZSM-5 catalysts are active systems for the decomposition of N2O, but their behaviour differs with respect to conditions and gas atmospheres. They all seem to obey a (nearly) first order dependency towards pmo> which can be rationalised by the two step kinetic model given by eqs. (2) and (3). A step like eq. (3) is quite well feasible, since the TM ions in ZSM-5 can be coordinated by several ligands simultaneously [18,22], The resulting rate expression is given by eq. (7). 

Further progress in the study of the Cu-Ni system awaited the preparation and careful characterization of alloy films of known bulk and surface composition. The essential step was taken by Sachtler and his co-workers 28, 88, 114) who prepared Cu-Ni alloy films by successive evaporation of the component metals in UHV. After evaporation the films were homogenized by heating in vacuum at 200°C. The bulk composition of the alloys was derived from X-ray diffraction, and the photoelectric work function of the films was also measured. A thermodynamic analysis, summarized by Fig. 13, indicated that alloy films sintered at 200°C should consist, at equilibrium, of two phases, viz., phase I containing 80% Cu and phase II containing 2% Cu. Evidence was presented that alloys within the... 

A cobalt-catalyzed method for arylation of heteroarenes including thiazole and benzothiazole was reported in 2003 <030L3607>. According to this report, the direct C-5 arylation of thiazole with iodobenzene was carried out in the presence of cobalt catalyst [Co(OAc)2/IMes] and cesium carbonate, and a complete reversal of arylation from C-5 to C-2 was observed with the bimetallic Co/Cu/IMes system. This report has been retracted as the laboratory of the senior author has not been able to reproduce the key results disclosed in the communication <06OL2899>. 

Solutes have differing solubilities in different liqnids dne to variations in the strength of the interaction of solnte molecnles with those of the solvent. Thus, in a system of two immiscible or only partially miscible solvents, different solutes become unevenly distribnted between the two solvent phases, and as noted earlier, this is the basis for the solvent extraction technique. In this context, solvent almost invariably means organic solvent. This uneven distribution is illustrated in Fig. 1.3, which shows the extractability into a kerosene solution of the different metals that appear when stainless steel is dissolved in aqueous acid chloride solution. The metals Mo, Zn, and Fe(III) are easily extracted into the organic solvent mixture at low chloride ion concentration, and Cu, Co, Fe(ll), and Mn at intermediate concentration, while even at the highest chloride concentration in the system, Ni and Cr are poorly extracted. This is used industrially for separating the metals in super-alloy scrap in order to recover the most valuable ones. 

The Co—Cu adlayer system is complex, but, due to the quasi epitaxy and negligible charge transfer, turns out to be a reasonable approximation to clean fee surfaces. 

Although the activity obtained by the MA route was not the highest in this case, the effectiveness of MA was still much higher than that of conventional catalyst. In some cases, MA is more effective than rapid solidification for making supersaturated precursors. An example is the Al-Co-Cu ternary system (11). The ranking of effectiveness of these methods may in general depend on the alloy system. 

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