Nickel deposit

The carbonyl process developed in 1899 by L. Mond is still used, though it is mainly of historic interest. In this the heated oxide is first reduced by the hydrogen in water gas (H2 + CO). At atmospheric pressure and a temperature around 50°C, the impure nickel is then reacted with the residual CO to give the volatile Ni(CO)4. This is passed over nucleating pellets of pure nickel at a temperature of 230°C when it decomposes, depositing nickel of 99.95% purity and leaving CO to be recycled. 

At normal current densities, about 96-98% of the cathodic current in a Watts solution is consumed in depositing nickel the remainder gives rise to discharge of hydrogen ions. The boric acid in the solution buffers the loss of acidity arising in this way, and improves the appearance and quality of the deposit. Although phosphides, acetates, citrates and tartrates have been used, boric acid is the usual buffer for nickel solutions. 

Some films containing deposited nickel together with copper were annealed at 500°C in order to ensure the homogenization of the alloys. After their cooling down to room temperature the X-ray diffraction patterns demonstrated phase segregation of the alloys similar to that described by Sachtler et al. (45). 

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. 

The aforementioned fact is also the basis for the separation of co-occurring metals from each other. Whenever feasible, such electrochemical separation is an interesting and effective technique, in principle. In practice, however, such selective deposition is not considered very feasible, particularly for elements which are close neighbors in the electrochemical series. For example, the decomposition potentials of nickel and of cobalt are -0.25 V and -0.27 V, respectively. This small 0.02 V difference makes the selective deposition of nickel, leaving cobalt in the solution, or vice versa, rather difficult to achieve in practice. On the other hand, it is quite easy to co-deposit nickel and cobalt and to obtain an alloy. 

I-M Chan, T-Y Hsu, and FC Hong, Enhanced hole injections in organic light emitting devices by depositing nickel oxide on indium tin oxide anode, Appl. Phys. Lett., 81 1899-1901, 2002. 

At least 75% of intratracheally deposited nickel chloride had been absorbed 72 h after the operation in rats [265]. Nickel chloride was cleared from the lungs of rats more rapidly after intratracheal instillation compared with nickel oxide [266], the slower clearance being attributed to an increased solubility of nickel chloride compared with the oxide. 

Diffusion Barriers. Diffusion barriers are used in the production of various components in the electronic industry. For example, electrochemically deposited nickel is used as a barrier layer between gold and copper in electronic connectors and solder interconnections. In these applications the product is a trilayer of composition Cu/Ni/Au. In another example, Ni and Co are considered as diffusion barriers and cladding materials in the production of integrated circuits and multichip electronic packaging. In this case the barrier metal (BM), Co or Ni, is the diffusion barrier between conductor and insulator (i.e., Cu and insulator), and the product trilayer is of composition Cu/BM/insulator. The common couple in these applications is the Cu/BM bilayer (BM, the diffusion barrier metal Co, Ni, or Ni-Co alloy). 

Although the concept of phase is well defined thermodynamically, here phase refers to a mechanically separable homogeneous part of an otherwise heterogeneous system. The concept of phase change refers here to a change in the number present or in the nature of a phase or phases as a result of an imposed condition such as temperature or pressure. To clarify and illustrate the topic at hand, we use the specific cases of electrolessly deposited nickel and electrodeposited cobalt. 

In some instances, to improve solderability, tin is deposited on nickel surfaces. In a short time, however, interdiffusion of the two metals results in the growth of an inter-metallic NiSn3 compound that is much less amenable to soldering. For tin over elec-trolessly deposited nickel surfaces, the interdiffusion results in pores in both films. Pores are to be avoided, of course, if conductivity and/or contact resistance is an issue. 

On heating, the solution hydrolyzes depositing nickel hydroxide. 

Tanaka I, Ishimatsu S, Matsuno K, et al. 1985. Biological half time of deposited nickel oxide aerosol in rat lung by inhalation. Biol Trace Element Res 8 203-210. 

In essence, what happens is that a substance present in solution (hypophosphate, say) gets electrochemically oxidized and in this process puts some electrons into the metallic catalyst patch, and these electrons then serve to neutralize the Ni2+ ions in solution and deposit nickel on the substrate. However, some phosphoms is built into the deposit also, and hydrogen is co-evolved along with the deposition of nickel cobalt. Hence, it seems reasonable to write the reactions thus ... 

The reduction of coumarin (1) mentioned in Section 57.2.4 is typical of the fate of a group of levellers used in nickel plating which have in common the groups (15). It has been recognized that the depositing nickel may function as a hydrogenation catalyst and that this would certainly imply adsorption of the alkene on the nickel surface. The vapour phase hydrogenation of ethylene catalyzed by nickel is said to be most rapid when nickel films have the (110) planes preferentially exposed,26 which may imply that the alkene function shows preferential adsorption on some planes. 

FIGURE 2.7 Etch profiles of microchannels obtained by wet etching (a) and dry reactive ion etching (b). In (a), the more rounded profile was obtained with direct wet etching using a PDMS channel mold (50 im in width), whereas the trapezoidal profile (dotted curve) was made with the deposited nickel layer as the etch mask (150 im in width) [125]. Reprinted with permission from Elsevier Science. 

Metal ion and halide impurities are an issue in ionic liquids with discrete anions. As we have demonstrated in Chapter 11.5 Li+ (and K+) are common cationic impurities, especially in the bis(trifluoromethylsulfonyl)amides which typically contain 100 ppm of these ions from the metathesis reaction. Although Li and K are only electrodeposited in the bulk phase at electrode potentials close to the decomposition potential of the pyrrolidinium ions, there is evidence for the underpotential deposition of Li and K on gold and on other rather noble metals. For a technical process to deposit nickel or cobalt from ionic liquids the codeposition of Li and/or K, even in the underpotential deposition regime, has to be expected. 

Finally the nickel carbonyl passes to the decomposer, which is filled with nickel shot at 200° C. The carbonyl decomposes, depositing nickel op the shot, which is kept moving to prevent its cohering to... 

The sublimed salt is slowly soluble in hot water, yielding a clear solution, which may be boiled without decomposition. Berthelot 6 states that the solution on standing in air deposits nickel monoxide. This, however, is not the case with the pure substance. The density of the sublimed salt is 4-64 at 28° C. 

The V and Ni images show that the left particle has been in the unit for a long time while the right particle is very new. In the older particle, the vanadium distribution is nearly homogeneous while the new particle shows vanadium diffusing from the external surface. This observation shows that vanadyl as well as nickel porphyrins must crack on the external catalyst skin. Vanadium migration then occurs after the metal deposit is on the catalyst surface. The Ni distribution confirms the age of the pair, but also reveals that edge enhancement persists on very old particles. This confirms that the deposited nickel has very little or no mobility in the FCC unit. 

Gauthier4 prepares the finely divided nickel by depositing nickel oxide on glass beads of 2 mm. diameter, and reducing at 330° C. 

At temperatures above 300°C Holinski found that molybdenum disulphide produced embrittlement of stainless steel. He suggested that free sulphur released at these temperatures reacted with nickel in austenitic alloys to deposit nickel sulphide preferentially at grain boundaries, thus leading to a form of stress corrosion. Knappwost similarly reported that molybdenum disulphide reacted with iron at 700°C to produce ferric sulphide and free molybdenum, and Tsuya et al showed that it reacted more rapidly with iron and nickel than with silver or copper in a vacuum of 10 Torr above 500°C. The reaction with copper was in fact slow above 500°C but very rapid about 700 C. 

Vest, C.E. and Bazzarre, D.F., Co-Deposited Nickel-Molybdenum Disulphide, Metal Finishing, p. 52, (Nov. 1967). 

Experiments in conditions A4 show that nickel deposition can be obtained from NiCp with a reduced quantity of hydrogen in the gas phase. It has been reported that nickel deposition from nickelocene without additional hydrogen requires high temperature (at least 350°C at atmospheric pressure) and leads to high carbon contamination. Stauf et obtained nickel films by evaporating nickelocene at low pressure only above 550°C. These films were also heavily contaminated with carbon. On the other hand, Dormans failed in depositing nickel with as carrier gas, because of premature decomposition of NiCp ... 

This allows a direct comparison of the ratio Vj2/(Vg + V3) in different conditions. Because reaction rate v is considered to be negligible, V3 Vg + Vg based on assumption of steady state. Thus, this molar ratio should be 2 i.e. equal to the number of molecules of CH formed for each half atom of deposited Ni. The rate of carbon incorporation per deposited nickel atom (i.e. the ratio yjy) is directly given by the carbon content of the films. As reaction (9) is related to C Hg, each ligand yields 5 carbon atoms, and ratio v /v is provided by (Vj + Hence, the following relation can be obtained ... 

The hydrolysis of urea is a slow step [93] a relatively long heating period (5-20 hr) is necessary to precipitate the nickel ions completely. Compared to impregnation, the amount of nickel deposited by deposition precipitation is relatively low. Nevertheless, due to a more homogeneous distribution of the active phase or its precursor, this method is often preferred [55,91,93,94]. In a recent optimization study, it was found that a higher nickel or urea concentration in the solution increases the amount of nickel deposited and shortens the time needed for the deposition. Nickel loadings up to 10.5 wt% were realized in a time frame of 5 hr [69,91 ]. This method is, of course, not restricted to nickel deposition other species, e.g., manganese, can be deposited similarly [93]. 

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