Sensitization high nickel alloys

Copper alloys (brass, bronze, etc.) for very shock-sensitive perchlorate salts Aluminum (dissolves at room temperature) High nickel alloys (dissolves), others Cotton Wood... 

For applications requiring corrosion-resistant alloys, either low-carbon or stabilized stainless steels such as Type 321 SS are normally selected. Sensitization-induced polythionic acid corrosion is a concern in such applications. High-nickel alloys and copper-based alloys often corrode rapidly in the presence of high-temperature sulfur compounds. 

Alloy contents of stainless steels, particularly nickel, determine the sensitivity of the metal to SCC. Ferritic stainless steels, which are nickel-free, and the high-nickel alloys are not subject to SCC. An alloy with a nickel content of greater than 30% is immime to SCC. The most common grades of stainless steel (304, 304L, 316, 316L, 321, 347, 303, 302, and 301) have nickel contents in the range of 7-10% and are the most susceptible to SCC. 

Coriou, M., Grail, L, Mahieu, C. and Pelas, M., Sensitivity to Stress Corrosion and Intergranular Attack of High-nickel Austenitic Alloys , Corrosion, 22, 280 (1966)... 

The earlier discussion (7.3) leads one to expect absorption and enhancement effects in these high-temperature alloys. For example, the results for nickel will be very sensitive to the iron content. Nickel Ka has a wavelength about 0.1 A shorter than that of the iron K edge (Figure 7-2), and a slight increase in the iron content consequently means an increased absorption of nickel Ka, which tends to reduce the apparent nickel content (negative absorption effect). Furthermore, this increased absorption of nickel Ka will enhance iron Ka, whence an... 

In many countries, nickel is the commonest sensitizer in women, causing nickel allergy incidence to be high in a series of reported patch tests [399,400]. Since 1930, the emphasis has shifted from sensitization at work to sensitization in the home by nickel-plated metal and objects made of nickel alloy. The age of onset has altered to teenagers and young women and the source is now cheap metal jewellery and fasteners on clothing such as jeans studs. Also sensitization in infancy has been reported. Nickel-sensitive patients do not... 

The most common microstructural effect on the corrosion resistance of nickel alloys is intergranular sensitization, as previously mentioned. This is the result of chromium carbide precipitation in many Ni-Fe-Cr alloys but can result from intermetallic Mu-phase precipitation in low-carbon highly alloyed materials such as alloy C-276 (UNS N10276). Several standard IGA tests (discussed in the Intergranular Corrosion section) are available for determining (1) if stabilized alloys have been properly annealed to prevent subsequent sensitization, and (2) if nonstabilized alloys are free from significant sensitization as produced. 

One of the most important attributes of nickel with respect to the formation of corrosion-resistant alloys is its metallurgical compatibility with a number of other metals, such as copper, chromium, molybdenum, and iron. A survey of the binary phase diagrams for nickel and these other elements shows considerable solid solubility, and thus one can make alloys with a wide variety of composition. Nickel alloys are, in general, all austenitic alloys however, they can be subject to precipitation of intermetallic and carbide phases when aged. In some alloys designed for high-temperature service, intermetallic and carbide precipitation reactions are encouraged to improve properties. However, for corrosion applications, the precipitation of second phases usually promotes corrosion attack. The problem is rarely encountered because the alloys are supplied in the annealed condition and the service temperatures rarely approach the level required for sensitization. 

Raney nickel is a useful catalyst for hydrogenations at mild conditions. It is, however, sensitive to poisoning and not very stable at high temperatures. Another disadvantage is that regeneration is not always possible in many cases the catalyst must be melted with aluminium until the right Al-Ni alloy is formed. Then the preparation procedure has to be repeated again. Moreover, the preparation procedure is not very reproducible. 

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