Nickel lattice structure

The most important undesired metallic impurities are nickel and vanadium, present in porphyrinic structures that originate from plants and are predominantly found in the heavy residues. In addition, iron may be present due to corrosion in storage tanks. These metals deposit on catalysts and give rise to enhanced carbon deposition (nickel in particular). Vanadium has a deleterious effect on the lattice structure of zeolites used in fluid catalytic cracking. A host of other elements may also be present. Hydrodemetallization is strictly speaking not a catalytic process, because the metallic elements remain in the form of sulfides on the catalyst. Decomposition of the porphyrinic structures is a relatively rapid reaction and as a result it occurs mainly in the front end of the catalyst bed, and at the outside of the catalyst particles. 

Fig. 5. Diffraction pattern, at 200 volts or 0.865 A., from oxygon atoms adsorbed upon the nickel surface in the arrangement of Fig. 7—called the 4-Structure. The two very bright spots are (820) Laue diffraction beams from the nickel lattice at their maximum intensity.

Fig. 6. Diffraction pattern, at 72 volts or 1.44 A., from the nickel surface covered by atoms of oxygen arranged in the 4-Structure (Fig. 7), the same surface which gave the pattern of Fig. 5. The single spot at the top is a (511) Laue diffraction beam from the nickel lattice.

Nickel electrodes are usually based on nickel hydroxides. Several forms of nickel hydroxides and oxyhydroxides are involved in the electrochemical process of nickel electrodes, which have been described in literature as a-Ni(0H)2i j8-Ni(OH)2. 7-Ni(0H)2, -NiOOH and y-NiOOH . The three divalent nickel hydroxides have different chemical compositions, but all of them have a lattice structure of alternate layers, differing in the relative spacing of hexagonal structure. The starting material for the formation of the alkaline electrode is the a-form hydroxide which is denoted as a-Ni(OH)2.xH2O,2 where x varies between 0.5 and 0.7. 

As oxygen adsorbs on the nickel surface, the intensity of the diffraction pattern from the nickel lattice decreases because of the low penetrating power of the electrons. This rate of decrease with increasing exposure is approximately the same for an ion-bombarded surface which has been well annealed as for one which has received a small anneal. However, the diffraction patterns from the gas-lattice structures on the surface with the small anneal are much more intense than those from the gas-lattice structures on the well-annealed surface because of the different defect densities in the two cases. If the extinction of the pattern from nickel were caused by the presence of the gas-lattice structures, one should expect a greater rate of extinction for the surface having a small anneal. Since this is not the case, the major part of the ex-... 

The metallocyanates are a large class of compounds, the most widely studied of which are probably Prussian Blue (Na[FeFe(CN)fi]) in its various oxidation states and nickel hexacyanoferrate (Na2[NiFe(CN)6]). These materials can be prepared chemically or electrochemically as thin films on surfaces [200]. They differ from redox polymers in that, because of their lattice structure, there is significant interaction between the redox sites within the film and there is strong size-charge selectivity towards incorporated counter-ions. This arises because the counter-ions have to be accommodated within the lattice structure and this... 

One material that has wide application in the systems of DOE facilities is stainless steel. There are nearly 40 standard types of stainless steel and many other specialized types under various trade names. Through the modification of the kinds and quantities of alloying elements, the steel can be adapted to specific applications. Stainless steels are classified as austenitic or ferritic based on their lattice structure. Austenitic stainless steels, including 304 and 316, have a face-centered cubic structure of iron atoms with the carbon in interstitial solid solution. Ferritic stainless steels, including type 405, have a body-centered cubic iron lattice and contain no nickel. Ferritic steels are easier to weld and fabricate and are less susceptible to stress corrosion cracking than austenitic stainless steels. They have only moderate resistance to other types of chemical attack. 

Many catalysts have the fee structure. The arrangement of the atoms in the above-mentioned surfaces is depicted in Figure 5-17. Also shown is the munber of neighboring atoms and free valences of the surface atoms for tiie example of the nickel lattice [T33]. The highest number of free valences, namely five, occurs for the prismatic faces. 

Mixed metal oxide pigments are manufactured by high temperature (800-1000 °C) solid state reactions of the individual oxide components in the appropriate quantities. The preparation of nickel antimony titanium yellow, for example, involves reaction of Ti02, NiO and Sb203 carried out in the presence of ojg gen or other suitable oxidising agent to effect the necessary oxidation of Sb(iii) to Sb(v) in the crystal lattice structure. 

The martensitic stainless steels normally contain 11-13% chromium. Martensite is a body-centered tetragonal structure that provides increased strength and hardness vs. the annealed stainlesses with other lattice structures. Sufficient carbon is added to permit martensite formation with rapid cooling. Other elements such as nickel or molybdenum may be added for improved corrosion resistance. 

In order for dopant atoms to be stabilized within a host lattice, both solvent/solute species must have similar electronegativities. If this prerequisite were not met, electron density would transfer to the more electronegative atoms, forming a compound with an entirely new lattice structure and distinct properties. For instance, the reaction of metallic aluminum and nickel results in nickel alumi-nide, NisAl, a compound with both ceramic and metallic properties. Such transformational alloys are in contrast to interstitial and substitutional alloys, in which the original solvent lattice framework is not significantly altered. 

These elements have a face centered lattice structure. Alloys of these elements may also be used. Carbon alloyed with nickel and chromium (austinetic stainless steel) can also be used. 

---