Surface of nickel

At their highest sensitivities, STM and AFM generate images that show how atoms are arranged on the surfaces they probe. At first, scientists used these tools to explore how atoms are arranged on surfaces. The example below shows individual atoms on the surface of nickel metal. 

A well-known example of adsorbate induced surface reconstruction is that of carbon on the (100) surface of nickel. Even though this surface already offers a four-fold coordination to the carbon atom in unreconstructed form, additional energy is gained by the so-called clock-anti-dock reconstruction shown in Fig. 5.8. Of course, it costs energy to rearrange the surface nickel atoms, but this investment is more than compensated by... 

Taking into account the results of all the above-listed experiments, it is possible to conclude that these experimental methods indeed indicate the interaction of the two gases on the surface of nickel at temperatures close to room temperature. 

The only conclusions that can be drawn from our experiments concerning the role of oxygen in these interactions are (1) oxygen chemisorption is faster than the subsequent interaction, and (2) oxygen can react with hydrogen on the surface of nickel in the adsorbed layer at room temperature. 

Fig. 17. Thermograms recorded during the adsorption of doses of oxygen at the surface of nickel-oxide samples containing preadsorbed oxygen, the cold trap being cooled (A) or not cooled (B) (71). 

For reaction, e.g. the dissociation, of hydrogen at the surface of nickel, the fraction of molecules capable of so dissociating will be... 

The solution to the Christoffel equation for a given material can be plotted in k-space as surfaces of k/w. These are known as slowness surfaces, because they represent the reciprocal of phase velocity. Figure 11.1 is a representation of slowness surfaces of nickel in three-dimensional k-space. Because longitudinal waves have the greatest velocity and therefore... 

On the other hand, it must be appreciated from the work of Engell and Hauffe (37) that below 200°C. the surface of nickel oxide is covered... 

At this the reaction rate, r, is the amount of CH4 reacted per square meter of the apparent surface of nickel per hour, measured in cubic centimeters reduced to 0°C and 760 mm Hg R is the gas constant in cal K-1 mol-1. 

We conclude, therefore, that the mechanisms of catalytic cracking reactions on nickel metal and nickel carbide are closely comparable, but that the latter process is subject to an additional constraint, since a mechanism is required for the removal of deposited carbon from the active surfaces of the catalyst. Two phases are present during reactions on the carbide, the relative proportions of which may be influenced by the composition of the gaseous reactant present, but it is not known whether the contribution from reactions on the carbide phase is appreciable. Since reactions involving nickel carbide yielded products other than methane, surface processes involved intermediates other than those mentioned in Scheme I, although there is also the possibility that if cracking reactions were confined to the metal present, entirely different chemical changes may proceed on the surface of nickel carbide. 

Table 2 Correlation of theoretical predictions and experiment for hydrogen absorbed on the 100 surface of nickel...

Humic total loss surface of Nickel significant... 

Nitric acid may also be used to treat surfaces of nickel and chrome alloys, in metal etching and in treatment of refractory metals such as zirconium. 

Reaction between Carbon Monoxide and the Surface of Nickel... 

The original objects on the surface of nickel spheres have been produced in experiments with fullerene solutions [7-8],... 

However, when hydrocarbons with fullerenes mixed, carbon nanotubes up to 50 nm in diameter are formed on the surface of nickel microparticles. Nanotubes are not perpendicular to the surface (as in pyrolysis), but they are parallel to it. Tubes on the surface of particles form the continuous net (Fig. 11). 

The density functional theory and the cluster model approach enable the quantitative computational analysis of the adsorption of small chemical species on metal surfaces. Two studies are presented, one concerning the adsorption of acetylene on copper (100) surfaces, the other concerning the adsorption of ethylene on the (1(X)) surfaces of nickel, palladium and platinum. These studies support the usefulness of the cluster model approach in studies of heterogeneous catalysis involving transition metal catalysts. 

Results pointing in the same direction were obtained recently by Schuit and De Boer (17), who found that activated adsorption of hydrogen occurs only on a partially oxidized surface of nickel supported on silica (3 1) but not on a thoroughly reduced surface. According to Schuit and De Boer, very prolonged evacuation or heating of a reduced nickel catalyst in an inert atmosphere leads to a slow activated hydrogen adsorption. This effect, however, disappears on renewed careful reduction... 

Rieder KH, Stocker W (1985) The coverage-dependent ordering of chemisorbed hydrogen on the (110) surface of nickel. Surf Sci 164 55... 

Nickel oxide in the upper phase is reduced with hydrogen to metallic nickel, which has the ability to hydrodecompose the C—C bond of hydrocarbons. This nickel oxide is dissolved away in a dilute hydrochloric acid and leaves the exposed surface of nickel aluminate. This nickel aluminate is slowly decomposed so as to form very fine particles of nickel on heating over 500° in a stream of hydrogen. 

Different chemisorbed ionic species may exist on the surface of nickel oxide 0 (ads), 0 (ads), 02-(ads). From a consideration of the enthalpy changes of gas-phase reactions involving oxygen species. Winter (46) concluded that the most likely species first formed on the chemisorption of oxygen is 02 (ads), followed by O (ads). The direct formation of 02-(ads) was shown to be most unlikely and the following results are in agreement with this conclusion. 

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