Metal deposition factors affecting

In principle, any one of these could be the rate-determining step (r.d.s.). However, it was foimd, by the use of a variety of experimental techniques, that ionic migration through the SEI is the rate-determining step for many systems. In addition, it was found that the rate of nucleation of the metal deposit is affected by the interfacial resistance. This transport process is a key factor in the operation of non-aqueous SEI batteries. 

Actually, it is recognized that two different mechanisms may be involved in the above process. One is related to the reaction of a first deposited metal layer with chalcogen molecules diffusing through the double layer at the interface. The other is related to the precipitation of metal ions on the electrode during the reduction of sulfur. In the first case, after a monolayer of the compound has been plated, the deposition proceeds further according to the second mechanism. However, several factors affect the mechanism of the process, hence the corresponding composition and quality of the produced films. These factors are associated mainly to the com-plexation effect of the metal ions by the solvent, probable adsorption of electrolyte anions on the electrode surface, and solvent electrolysis. 

Another important factor affecting carbon deposition is the catalyst surface basicity. In particular, it was demonstrated that carbon formation can be diminished or even suppressed when the metal is supported on a metal oxide carrier with a strong Lewis basicity [47]. This effect can be attributed to the fact that high Lewis basicity of the support enhances the C02 chemisorption on the catalyst surface resulting in the removal of carbon (by surface gasification reactions). According to Rostrup-Nielsen and Hansen [12], the amount of carbon deposited on the metal catalysts decreases in the following order ... 

Something of the complexity of factors affecting the efficiency of metal deposition—the competing reaction always being H co-deposition—can be seen in Fig. 7.171 where there is a maximum in chromium deposition efficiency at about 200 g... 

K. H. Dahmen, Variations on Nickel Complexes of the Vic-Doximes, An Understanding of Factors Affecting Volatility Toward Improved Precursors for Metal-Organic Chemical Vapor Deposition of Nickel, Chemistry of Materials, Vol.lO, 1998, pp.2525-2532. 

There are two major factors which have to be considered in the process of electrochemical metal deposition. First, thermodynamics and growth properties of 2D Me and 3D Me phases can be treated in a similar manner to that for Me deposition from vapor or electrolyte phases. Second, the properties of the electrolyte phase strongly affect the structure of the substrate/electrolyte interface, the kinetics of the mass and charge transfer across it, and the kinetics of chemical reactions which can precede or follow the charge transfer. 

Typical reforming catalyst are bifunctional, with a metal function (Pt, Pt-Re, Pt-Ir, etc] and an acid function (chlorided alumina). During operation, along with the desired reactions, the deposition of carbonaceous material occurs over the metal and the acid sites (1). This coke is the most important factor affecting the lifetime of the catalyst. As a consequence of this deposition, the reactor temperature must be raised to maintain the same octane number In the reformate. The partially deactivated catalyst has different selectivity than the fresh one. This suggests that the coke is deposited to a different extent on the metallic and on the acid function, and that the more demanding reactions are preferentially deactivated (2). 

Electroless metal deposition at trace levels in the solution is an important factor affecting silicon wafer cleaning. The deposition rate of most metals at trace levels depends mainly on the metal concentration and some may also depend on the interaction with other species as well. For copper the deposition rate at trace levels in HF solutions is different for n and p types. It depends on illumination for p-Si but not for n-Si. It is also different in HF and BHF solutions. In a HF solution the deposition process is controlled by both the supply of minority carriers and the kinetics of cathodic reactions. Thus, a high deposition rate occurs on p-Si only when both and illumination are present. In the BHF solution, the corrosion process is limited by the supply of electrons for p-Si whereas for n-Si it is limited by the dissolution of silicon because the reaction rate is indepaidmt of concentration and illumination. The amount of copper deposition does not correlate with the corrosion current density, which may be attributed to the chemical reactions associated with hydrogen reduction. More information on trace metal deposition can be found in Chapters 2 and 7. 

Following deposition of an active metal upon a ceria surface, it is possible to study chemisorption on a surface that models many of the important aspects expected for actual ceria supported catalysts. Surface techniques offer the possibility to identify where the adsorbates are located and to identify intermediates that are formed in their interaction. By comparison of ceria surfaces, with and without metal, the synergisms between metal and support can be deduced. By controlled metal deposition, it is possible to study the effects of loading and particle size. By selected preparation of the ceria substrate it is possible to vary factors which may affect the interaction between the metal particle and the ceria, sueh as structure, defeet concentration or oxidation state of the ceria. The goal of chemisorption studies, summarized below, is to relate all these factors to the interaction of the model catalyst with particular adsorbates. 

Research on supported Ni catalysts, used for steam reforming and other applications " , has dealt with factors affecting their activity and stability. Catalyst formulation and the extent to which interaction occurs between NiO and the support are important factors influencing the reduction of NiO to Ni in the catalyst and the catalysts subsequent behavior. The influence of the support on the metal is illustrated by NiO on AI2O3 or MgO. It is well known that NiO deposited on oxide supports is less readily reduced than bulk NiO. Furthermore, growth of crystallites of the metal oxide can be retarded by a suitable support. For instance, the presence of MgO retards the growth of NiO. When NiO is calcined at 500°C for 4 h, NiO crystallites increase to about 30 nm, whereas in a NiO/40% MgO solid solution, the crystallites grow to only 8 nm (Fig. 1). ... 

The major factors affecting the quality of soils close to mining industries are (i) change of soil pH, i.e. acidification or alkalisation, as well as (ii) accumulation of trace elements, particularly of heavy metals. Because those soils are contaminated mainly by atmospheric depositions, it is difficult to specify the... 

Another factor affecting the relative corrosive rate resulting from rain is the orientation of the metal surface. In areas of heavy industrial pollution, skyward-facing metallic surfaces benefit from rain. In those areas where dry deposition is considerably greater than wet deposition of sulfur pollutants, the washing effect of rain predominates, and the corrosion rate is reduced. In areas having less pollution the situation is reversed and the corrosive action of the rain predominates. 

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