Nickel aqueous corrosion

Some of the nickel-based alloys were designed to withstand high temperature and dry or gaseous corrosion whereas others are mainly designed to resist low-temperature (aqueous) corrosion. Nickel-based alloys used for low temperature aqueous or condensed systems are generally known as corrosion-resistant alloys (CRA). Only the corrosion performance of commercially available CRA will be addressed in this chapter. 

At the other extreme, the oxide layers on aluminum, beryllium, titanium, vanadium, chromium, nickel, and tantalum are very insoluble in water at intermediate pH values and do not have easily accessible reduced states with higher solubility. The oxide films on those metals are therefore highly protective against aqueous corrosion. 

Draley, J. E., TID-7587, "Aqueous Corrosion of 1100 Aluminum and of Aluminum-Nickel Alloys,"... 

Tras CHAPTER HIGHLIGHTS the coiTOsion resistance of nickel and its alloys and identifies relevant ASTM standards associated with their evaluation. The test technique selected ultimately will depend upon the specific alloy involved, the type of corrosion in question, or the end application, or a combination thereof. The following discussions will deal primarily with aqueous corrosion and the nickel-base (greater than about 30 % nickel) alloys designed for aqueous corrosion resistance. High-temperature gaseous corrosion will be addressed in other sections. 

Nickel is a metal characterized by soft, ductile, smelting and converting properties. Its standard electrochemical potential is -0.24V. The chemical compounds of nickel are mainly found in 2nd oxidation states, rather than the 3rd and 4th ones. It dissolves in mineral acids, but insensitive to bases (alkalis). In the atmospheric environment and many aqueous solutions nickel has the ability to passivity in a fairly wide pH range. Thanks to its passivity it has high resistance to corrosion in many environments (Trzaska Moszczynski, 2008). 

The behavior of weathering low-alloy steels in aqueous corrosion tests and applications is unpredictable. In 1953, early tests on weathering steels containing copper, chromium, phosphorus, and nickel showed superior... 

Cobalt. Cobalt is not generally used as a primary alloying element in materials designed for aqueous corrosion resistance. However, cobalt imparts unique strengthening characteristics to alloys designed for high-temperature service. Cobalt, like iron, increases the solubility of carbon in nickel-base alloys, therefore increasing the resistance to carburization. 

The selection of materials for use in many industrial environments, including supercritical thermal power plants (SCTPPs) and Supercritical Water Oxidation (SCWO) systems requires a broad study of the forms and the rates of corrosion of various metals and alloys in supercritical (T > 374°C) aqueous environments. Nickel is an important component of many corrosion resistant alloys and is a classic model for corrosion studies. Extensive electrochemical polarization studies of this metal in... 

Corrosion. Aqueous solutions of citric acid are mildly corrosive toward carbon steels. At elevated temperatures, 304 stainless steel is corroded by citric acid, but 316 stainless steel is resistant to corrosion. Many aluminum, copper, and nickel alloys are mildly corroded by citric acid. In general, glass and plastics such as fiber glass reinforced polyester, polyethylene, polypropylene, poly(vinyl chloride), and cross-linked poly(vinyl chloride) are not corroded by citric acid. 

Asahi also reports an undivided cell process employing a lead alloy cathode, a nickel—steel anode, and an electrolyte composed of an emulsion of 20 wt % of an oil phase and 80 wt % of an aqueous phase (125). The aqueous phase is 10 wt % K HPO, 3 wt % K B O, and 2 wt % (C2H (C4H )2N)2HP04. The oil phase is about 28 wt % acrylonitrile and 50 wt % adiponitrile. The balance of the oil phase consists of by-products and water. The cell operates at a current density of 20 A/dm at 50°C. Circulated across the cathode surface at a superficial velocity of 1.5 m/s is the electrolyte. A 91% selectivity to adiponitrile is claimed at a current efficiency of 90%. The respective anode and cathode corrosion rates are about mg/(Ah). Asahi s improved EHD process is reported to have been commercialized in 1987. 

The corrosion resistance of low-alloy steels is not significantly better than that of mild steel for aqueous solutions of acids, salts, etc. The addition of 0.5% copper forms a rust-colored film preventing further steel deterioration small amounts of chromium (1%) and nickel (0.5%) increase the rust... 

Willert, H., Investigations of the Corrosion Resistance of a 13%Cr Steel in Aqueous Salt Solutions , Neue Huelle, 11 72 (1966) C.A., 65, 14954b Tousek, J., Passivity of Nickel , Colleclion Czech. Chem. Commun., 31, 3083 (1966) C.A.,... 

The nominal compositions of commercially pure wrought nickel and the main types of modern corrosion-resistant nickel alloys are given in Table 4.21 some of these supersede earlier variants no longer in production. Applications of nickel alloys are not confined to those where corrosion resistance to aqueous solutions is a prime requirement, and the complete... 

Compared with ferritic carbon and low-alloy steels, relatively little information is available in the literature concerning stainless steels or nickel-base alloys. From the preceding section concerning low-alloy steels in high temperature aqueous environments, where environmental effects depend critically on water chemistry and dissolution and repassivation kinetics when protective oxide films are ruptured, it can be anticipated that this factor would be of even more importance for more highly alloyed corrosion-resistant materials. 

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