Metallic nickel films

The adsorption of CO2 on metallic nickel films has been studied in both the presence and absence of oxygen. An i.r. spectroscopic study of the simultaneous adsorption of COg and O2 on nickel has shown the formation of carbonate-carboxylate structures on the nickel surface. The adsorption of CO2 on nickel in the temperature range —196 to 0 °C has been found to be irreversible, the molecules being adsorbed at two surface sites within the limits of the monolayer. Above 100 °C, dissociative adsorption of CO2 takes place with the formation of CO. ... 

Under severe conditions and at high temperatures, noble metal films may fail by oxidation of the substrate base metal through pores in the film. Improved life may be achieved by first imposing a harder noble metal film, eg, rhodium or platinum—iridium, on the substrate metal. For maximum adhesion, the metal of the intermediate film should ahoy both with the substrate metal and the soft noble-metal lubricating film. This sometimes requires more than one intermediate layer. For example, silver does not ahoy to steel and tends to lack adhesion. A flash of hard nickel bonds weh to the steel but the nickel tends to oxidize and should be coated with rhodium before applying shver of 1—5 p.m thickness. This triplex film then provides better adhesion and gready increased corrosion protection. 

This conclusion was additionally confirmed by Palczewska and Janko (67) in separate experiments, where under the same conditions nickel-copper alloy films rich in nickel (and nickel films as well) were transformed into their respective hydride phases, which were proved by X-ray diffraction. The additional argument in favor of the transformation of the metal film into hydride in the side-arm of the Smith-Linnett apparatus consists of the observed increase of the roughness factor ( 70%) of the film and the decrease of its crystallite size ( 30%) after coming back from low to high temperatures for desorbing hydrogen. The effect is quite similar to that observed by Scholten and Konvalinka (9) for their palladium catalyst samples undergoing the (a — j8) -phase transformation. 

The initial rate constant values related to 10 mg of the metal film catalyst obtained from the kinetic plots (analogous to those represented in Fig. 15) diminishes by about one order of magnitude as a consequence of nickel film preexposure to atomic hydrogen (i.e. after transformation into... 

Beeck at Shell Laboratories in Emeryville, USA, had in 1940 studied chemisorption and catalysis at polycrystalline and gas-induced (110) oriented porous nickel films with ethene hydrogenation found to be 10 times more active than at polycrystalline surfaces. It was one of the first experiments to establish the existence of structural specificity of metal surfaces in catalysis. Eley suggested that good agreement with experiment could be obtained for heats of chemisorption on metals by assuming that the bonds are covalent and that Pauling s equation is applicable to the process 2M + H2 -> 2M-H. 

Fig. 11-13. Anodic polarization curve of a metallic nickel electrode in a sulfuric add solution transpassivation arises at a potential relatively dose to the flat band potential because of p-type nature of the passive oxide film. [From Sato, 1982.]...

A differenf approach has been ufilised in fhe case of processing mefallic nickel fhin films by AID [161]. During fhe firsf sfage, NiO fhin films have been deposifed using one AID cycle of ( 5115)2 and H2O. The NiO layer formed was then reduced to metallic nickel by pulsing hydrogen radicals into the reactor. 

Brissonneau L, Vahlas C (2000) Precursors and operating conditions for the metal-organic chemical vapor deposition of nickel films. Annales De Chimie-Science Des Materiaux 25(2), 81-90... 

To prepare metal hexacyanoferrate films, very frequently the following procedure was followed first a film of the respective metal, for example, cadmium [79], copper [80], silver [81], or nickel [82, 83] was elec-trochemically plated on the surface of a platinum electrode, and that was followed by chemical oxidation of the metal film in a solution of K3[Fe(CN)6], leading to the formation of the metal hexacyanoferrates. The same method has been used to produce films of nickel hexacyanoruthen-ate and hexacyanomanganate using the appropriate anions [83]. It is also possible to perform the oxidation of the deposited metals in solutions containing hexacyano-ferrate(II) by cyclic oxidation/reduction of the latter. In a similar way, films of copper heptacyanonitrosylferrate have been deposited [84]. 

The exchange of methane with deuterium has been followed on nickel films 12), on a cobalt-thoria Fischer-Tropsch catalyst 13) and on films of rhodium, platinum, palladium, and tungsten 30). The important features of the exchange over the metal films may be summarized as follows ... 

The exchange of neopentane with deuterium has been examined over a number of metal films by Kemball ( ) and over nickel films at higher temperatures by Rowlinson et al. (29). This compound has attracted interest because an a-P multiple exchange process cannot operate, and an process is necessary if more than three hydrogen atoms are to be exchanged during a single sojourn of the molecule on the catalyst. 

Tubules prepared from diacetylenic phospholipids (21) Copper and nickel films Electron microscopy and X-ray fluorescence measurements indicated 20- to 30-nm metallic coatings on the interiors and exteriors of the tubules 356... 

He concludes that the first (associative) mechanism gives values nearest the observed heat of adsorption determined by Beeck (30), and is therefore accepted as nearest the truth (34) (Qo (calculated) = 42 kcal./ mole Qo (observed) = 58 kcal./mole). Experiments on tungsten and nickel films (Beeck (35), Trapnell (36), and more recent work in Rideal s laboratory) have shown that when ethylene is added to a clean metal surface ethane appears in the gas phase. A self hydrogenation mechanism must be operative and at least in these cases dissociation of ethylene must occur on the catalyst. It is suggested that the calculations might be complicated by the energy of bond strain in the adsorption of an ethylene molecule to the fixed lattice distances of the metal. 

The number of superimposed atom layers can be estimated on the following basis. According to Beeck and others (29), metal films condensed at low temperature in a high vacuum and warmed to room temperature are composed of crystallites with different orientations. The mirrors obtained in this way show the same optical behavior as crystalline compact material (47), especially after annealing in a high vacuum at an elevated temperature. The temperature coefficient of resistance, too, even that of the transparent nickel films in Table I, has the same order of magnitude as that of the compact metal therefore, it seems correct to use the atomic volume of the crystalline metals for estimating the... 

At 90°K., however, N2 has already been adsorbed at low equilibrium pressures by these metals, but at room temperature it is given off again (23). Mignolet (14) observed a change of Ai/1,2 = +0.21 volt of contact potential when he had N2 adsorbed on a nickel film at low temperatures. Hence electrons are shifted from the molecule to the metal on adsorption of the N2 molecule, which probably is to be attributed to the lone electrons of the N2 molecule. 

Electrons bound by the N2O molecules on adsorption come from the metal-electron gas, as is seen from Fig. 25, which shows the influence of adsorbed N2O on the resistance of a transparent nickel film at 90.3°K. 

In carbon monoxide the bond between the atoms depends, as in the N2O molecule, on an asymmetrical electron shift, electrons of the 0 atom moving toward the C atom, and the CO molecule having a dipole character. In this case, too, metal electrons are displaced toward the adsorbed molecule and taken from the electron gas, as shown by the change of the electrical resistance of thin nickel films on carbon monoxide adsorption (18). 

The lone electrons of the 0 atom in the H2O molecule can also become part of the electron gas in the metal surface and reduce its work function. So Schaaff (75) observed an increase of the photoelectric emission of platinum in the presence of water vapor. On the other hand an adsorbed layer of H2O molecules on the surface of a thin nickel film decreases the electric resistance of the film (18). 

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