Nickel shells

The strong influence of morphology and mixing is well illustrated with the composite particle investigation. These particles were composed of a nickel shell coated on spherical aluminum particles by hydrogen reduction in aqueous metal salt solution. The overall ratio of material in a particle was about 80 wt% Ni and 20 wt% aluminum. With these particles, the ratio of reactants was approximately the same as in the mixed powders, but the morphology of the reactants is radically different. 

Experience has shown that the finish on the part surface is a direct function of the mold finish, and that the mold finish is a direct function of the quality of the mold material. Excellent results have been obtained using high-quality, nickel-plated, tool steel molds and electroformed nickel shells. 

Nickel shells that are electroformed or vaporformed when suitably backed up and mounted in a frame are also excellent materials for large-volume runs. For activities of less than 50,000 parts per year, aluminum forgings of Alcoa grade No. 7075-T73 machines to the needed configuration will perform satisfactorily. They have the advantage of good heat conductivity, an important feature in RIM. 

The electroforming process is used for the production of single or low numbers of cavities, as opposed to others requiring many cavities. The process deposits metal on a master in a plating bath. Many proprietary processes exist. The master can be constructed of such materials as plastic, reinforced plastic, plaster, or concrete that is coated with silver to provide a conductive coating. The coated master is placed in a plating tank and nickel or nickel-cobalt is deposited to the desired thickness of up to about 0.64 cm (0.25 in.). With this method, a hardness of up to 46 RC is obtainable. To reinforce the nickel shell it is backed up with different materials (copper, plastic, etc.) to meet different applications. A sufficient thickness of copper allows for machining a flat surface to enable the cavity to be mounted into a cavity pocket. 

The mold was a nickel shell heated to 60C, with the mold halves mounted on a hydraulic frame, and the resin was injected using a Venus-Gusmer on-line mixing RTM machine at 3 bar injection pressure. The fill time and resin cure time were 2 and 10 min, respectively. 

Electroformed nickel shell tooling can be useful for high quality/ medium volume (such as RTM). FET Engineering, Kentucky, USA, has a die spot press allowing both halves of the tool to be placed outside the press with both cavities in the up position, allowing work on the tool while registration of both halves is maintained. Helisys rapid prototype machine and SNK digitizer have been installed. Vapor... 

FIGURE 4.61 Back of a porous TPN (technical porous nickel) shell with inserted temperature control pipes... 

Tooling. Forming operates primarily under the force of gravity and low-pressnre vacnnm, so structural requirements for molds are minimal. Because the plastic is kept below its melting point, cooling requirements are also minimal or nonexistent. Wood is a commonly used material of construction for forming, while higher performance molds can be constracted from nickel-coated epoxy or from electroformed nickel shells. 

It also forms compounds known as carbonyls with many metals. The best known is nickel tetracarbonyl, Ni(CO)4, a volatile liquid, clearly covalent. Here, donation of two electrons by each carbon atom brings the nickel valency shell up to that of krypton (28 -E 4 x 2) the structure may be written Ni( <- 0=0)4. (The actual structure is more accurately represented as a resonance hybrid of Ni( <- 0=0)4 and Ni(=C=0)4 with the valency shell of nickel further expanded.) Nickel tetracarbonyl has a tetrahedral configuration,... 

Shell Higher Olefin Process) plant (16,17). C -C alcohols are also produced by this process. Ethylene is first oligomerized to linear, even carbon—number alpha olefins using a nickel complex catalyst. After separation of portions of the a-olefins for sale, others, particularly C g and higher, are catalyticaHy isomerized to internal olefins, which are then disproportionated over a catalyst to a broad mixture of linear internal olefins. The desired fraction is... 

Shell Higher Olefins Process (SHOP). In the Shell ethylene oligomerization process (7), a nickel ligand catalyst is dissolved in a solvent such as 1,4-butanediol (Eig. 4). Ethylene is oligomerized on the catalyst to form a-olefins. Because a-olefins have low solubiUty in the solvent, they form a second Hquid phase. Once formed, olefins can have Htfle further reaction because most of them are no longer in contact with the catalyst. Three continuously stirred reactors operate at ca 120°C and ca 14 MPa (140 atm). Reactor conditions and catalyst addition rates allow Shell to vary the carbon distribution. 

For example, in Ni(CO) nickel metal having 28 electrons coordinates four CO molecules to achieve a total of 36 electrons, the configuration of the inert gas krypton. Nearly every metal forming a carbonyl obeys the 18-electron rule. An exception is vanadium, forming a hexacarbonyl in which the number of electrons is 35. This carbonyl, which has a paramagnetism equivalent to one unpaired electron, however, readily adds one electron to form a closed valence shell complex containing the V(CO)(, anion. 

Metals and alloys, the principal industrial metalhc catalysts, are found in periodic group TII, which are transition elements with almost-completed 3d, 4d, and 5d electronic orbits. According to theory, electrons from adsorbed molecules can fill the vacancies in the incomplete shells and thus make a chemical bond. What happens subsequently depends on the operating conditions. Platinum, palladium, and nickel form both hydrides and oxides they are effective in hydrogenation (vegetable oils) and oxidation (ammonia or sulfur dioxide). Alloys do not always have catalytic properties intermediate between those of the component metals, since the surface condition may be different from the bulk and catalysis is a function of the surface condition. Addition of some rhenium to Pt/AlgO permits the use of lower temperatures and slows the deactivation rate. The mechanism of catalysis by alloys is still controversial in many instances. 

Figure 5 Comparison of spectral profiles measured from a specimen of NiO using EDS and EELS. Shown are the oxygen K- and nickel L-shell signals. Note the difference in the spectral shape and peak positions, as well as the energy resolution of the two spectroscopies.

The cross-section for electron impact ionization has already been mentioned in Sect. 2.2.2.2 in connection with electron sources, and a variety of experimental and theoretical cross-sections have been shown in Fig. 2.18 for the particular case of the K-shell of nickel. The expression for the cross-section derived by Casnati et al. [2.128] gives reasonably good agreement with experiment the earlier expression of Gry-zinski [2.131] is also useful. 

Heat exchangers that utilize copper coils are potential candidates for galvanic corrosion due to dissolved copper salts interacting with the galvanized steel shell. This problem can be avoided by nickel plating the coils. The coils then can be separated from direct contact with the vessel via insulation. Also, it is preferable to conduct the water on the tube side of heat exchangers. 

In addition to the neutral nickel/phosphine complexes used in the Shell Higher Olefins Process (SHOP), cationic Ni-complexes such as [(mall)Ni(dppmo)][SbF6] (see Figure 5.2-7) have attracted some attention as highly selective and highly active catalysts for ethylene oligomerization to HAOs [106]. 

M. PeUarin, B. Baguenard, J. L. Vialle, J. Lerme, M. Broyer, J. Miller and A. Perez, Evidence for icosahedral atomic shell structure in nickel and cobalt clusters. Comparison with iron clusters , Chem. Phys. Lett. 217 349 (1994). 

Duplex tubes 1-in. O.D. X 16 ft, 0 in. long, 16 BWG steel outside, 16 BWG cupro-nickel inside No. = 578,1 V4 -in. triangular pitch Shell 36-in. O.D., 4 tube pass Film coefficients ... 

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