Cu-Ni system

It is particularly helpful that we can take the Cu-Ni system as an example of the use of successive deposition for preparing alloy films where a miscibility gap exists, and one component can diffuse readily, because this alloy system is also historically important in discussing catalysis by metals. The rate of migration of the copper atoms is much higher than that of the nickel atoms (there is a pronounced Kirkendall effect) and, with polycrystalline specimens, surface diffusion of copper over the nickel crystallites requires a lower activation energy than diffusion into the bulk of the crystallites. Hence, the following model was proposed for the location of the phases in Cu-Ni films (S3), prepared by annealing successively deposited layers at 200°C in vacuum, which was consistent with the experimental data on the work function. 

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... 

Fig. 18. Phase diagram for the Cu-Ni system calculated from two available sets of thermodynamic data (70).

The Pt-Au system (162) is analogous to the Cu-Ni system in that it exhibits a wide miscibility gap (below 1258°C), and one metal (gold)... 

The Cu-Fe, Cu-Ni and Fe-Ni phase diagrams are accepted from [2007Tur], [2002Leb] and [2007Kuz] respectively. In the Cu-Fe and Cu-Ni systems, metastable miscibility gaps in the liquid phase exist. However no liquid separation occurs in the Cu-Ni system. 

In the case of the Cu-Ni system at 888 K, we use the bulk diffusion coefficient before and behind the moving boundary equal to = 3.8 x 10-20 ni s-i [51], The grain boundary diffusion coefficient is evaluated from the empirical expression ... 

We used the mentioned results and the notion of size-induced solubihty diagram to discuss the particular case of the Cu-Ni nanosystem [82]. Here, we restricted ourselves to the thermodynamic study of melting and freezing. Our additional analysis on the example of the Cu-Ni system demonstrated that for... 

The replacement of the chloride on iodide electrolyte permits to determine the thermodynamics of the Cu-Ni system... 

However, closer examination showed that the Cu-Ni system, immediately after the interruption of current, acquires an open circuit potential (or a mixed potential) which hes above the nickel reversible potential and below the copper reversible potential. In addition, the pH of these solutions, i.e. pH = 4, does not allow the formation of nickel oxides on the surface of the nickel. Therefore, in accordance with the mixed potential theory, copper continues to deposit at the expense of nickel dissolution, forming a classic galvanic corrosion cell. This process does not... 

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