Nickel composition

Another important function of metallic coatings is to provide wear resistance. Hard chromium, electroless nickel, composites of nickel and diamond, or diffusion or vapor-phase deposits of sUicon carbide [409-21-2], SiC , SiC tungsten carbide [56780-56-4], WC and boron carbide [12069-32-8], B4C, are examples. Chemical resistance at high temperatures is provided by aUoys of aluminum and platinum [7440-06-4] or other precious metals (10—14). 

Composite Plating. An electroless nickel matrix can be used to securely bond diamonds to cutting tools, and electroless nickel—diamond composites are also used (see Tool materials). The NYE-CARB process gives a siUcon carbide—electroless nickel composite that has extremely high abrasion resistance (49). Electroless nickel—Teflon composites are being promoted as low friction materials. 

It was assumed that the nickel crystallites are rapidly enveloped in a skin of a copper-rich alloy, from which diffusion towards the center of each crystallite then takes place. If xx and x2 are the atomic fractions of copper in the two equilibrium phases and x is the atomic fraction of copper in the alloy film under consideration, then the crystallites in the annealed film may have a variety of forms. Solid solutions occur at either end of the composition range but the values of Xi and x2 at 200°C are <0.1 and 0.8. Hence, over much of the composition range (i.e., where x lies between X and xi), the Cu-Ni films should consist of crystallites with a kernel which is almost pure nickel (composition xi) enveloped in a skin of a copper-rich alloy (composition x2). Eventually, when x is only slightly larger than Xi, the alloy skin does not completely surround the nickel crystallites small patches of alloy (x2) and almost pure nickel ( ci) are both exposed. 

Waterfowl feeding in areas subjected to extensive nickel pollution — such as smelters and nickel-cadmium battery plants — are at special risk because waterfowl food plants in those areas contain 500 to 690 mg Ni/kg DW (Eastin and O Shea 1981). Dietary items of the ruffed grouse (Bonasa umbellus) near Sudbury, Ontario, had 32 to 95 mg Ni/kg DW, whereas nickel concentrations in grouse body tissues usually contain less than 10% of the dietary level. Nickel concentrations in aspen (Populus tremula) from the crop of ruffed grouse near Sudbury ranged from 62 mg/kg DW in May to 136 mg/kg DW in September (Chau and Kulikovsky-Cordeiro 1995), which shows the role of season in dietary nickel composition. 

I. Apachitei, Synthesis and Characterisation of Autocatalytic Nickel Composite Coatings on Aluminium, PhD-thesis, Delft University of Technology (2001). 

The first publication on CHIM (Ryss and Goldberg, 1973) contains some examples of the successful applications of the method. For ground mode CHIM these include investigations of known polymetallic ore bodies at Altay and the copper-nickel composition at depths of 10-100 m of ore bodies in the Kola peninsula. The detection of copper-nickel ores in boreholes by logging mode CHIM is demonstrated. 

Fig. 21. Dependence of exchange current density for the hydrogen electrode reaction on nickel composition for Pd, Ni, and their alloys (8S).

W. Li, T. Qiu, L Wang, S. Ren, J. Zhang, L. He, X. Li, Preparation and Electromagnetic Properties of Core/Shell Polystyrene Polypyrrole Nickel Composite Microspheres. ACS Appl. Mater. Interfaces 2013,5,883-891. 

Corrosion pitting in seawater is observed largely above 40% Ni because pit growth is favored by passive-active cells (see Section 6.5), and such cells can operate only when the alloy is passive—that is, in the range of high nickel compositions. Practically, this distinction is observed in the specification of materials for seawater condenser tubes in which pitting attack must be rigorously avoided. The cupro nickel alloys are used (10-30% Ni), but not Monel (70% Ni-Cu). 

The critical compositions for passivity in the Cr-Ni and Cr-Co alloys, equal to 14% Cr and 8% Cr, respectively, can also be related to the contribution of electrons from nickel or cobalt to the unfilled rf-band of chromium [49]. In the ternary Cr-Ni-Fe solid solution system, electrons are donated to chromium mostly by nickel above 50% Ni, but by iron at lower nickel compositions [50]. Similarly, molybdenum alloys retain in large part the useful corrosion resistance of molybdenum (e.g., to chlorides) so long as the d-band of energy levels for molybdenum remains unfilled. In Type 316 stainless steel (18% Cr, 10% Ni, 2-3% Mo), for example, the weight ratio of Mo/Ni is best maintained at or above 15/85, corresponding to the observed critical ratio for passivity in the binary molybdenum-nickel alloys equal to 15 wt.% Mo [51]. At this ratio or above, passive properties imparted by molybdenum appear to be optimum. 

In general, the highest resistance to uniform corrosion is obtained with the nickel-bearing austenitic types, and, in general, the highest nickel-composition alloys in this class are more resistant than the lowest nickel compositions. For... 

Table 2.64 Tensile Properties of AI2O3-Whisker-Nickel Composites at 25 and 1000 °C(5)...

Nickel and many of its alloys generally have exceptional resistance to stress-corrosion cracking [133]. In most situations, higher nickel compositions have more resistance to stress corrosion by hot 50% NaOH, but under aerated conditions, nickel-chromium alloys are superior [134]. 

Other materials also can be co-deposited with nickel. These include silicon carbide, which improves wear resistance, and PTFE, which provides some lubricity and reduces the tendency of process streams to erode the nickel composition [145]. 

Figure 4.15 SEM photographs of the nickel composite membrane (a) and its cross-sectional view (b) (Haag et al., 2007).

FIG. 6—Corrosion scheme for duplex nickel composite showing lateral penetration in the bright nickel layer, which heips prevent perforation of the substrate [fO]. 

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