Nickel corrosion characteristics

Potential-current density (E-i) curves, which have been determined for a number of the austenitic cast irons and also for the nickel-free ferritic irons, indicate that in general the austenitic cast irons show more favourable corrosion characteristics than the ferritic irons in both the active and passive states. 

The previous paragraph assumes that the ethanol will be dry (containing no water) and contain only very small amounts of contaminants such as chloride and sulfate ions that would greatly increase the corrosivity of ethanol. Ethanol produced for fuel purposes in the past has contained up to 5 volume percent water and ion concentrations that made it much more corrosive than pure ethanol [3.7]. For an ethanol fuel with these corrosion characteristics, it was found that aluminum and steel could be coated with cadmium, hard chromium, nickel, or anodized aluminum to make them compatible. Coatings such as zinc, lead, and phosphate were found to be inadequate to prevent corrosion [3.7]. 

Agarwal, D. C., Heubner, U., and Herda, W., Corrosion Characteristics and Applications of Newer High and Low Nickel Containing Ni-Cr-Mo Alloys, Paper 179, Corrosion/91, Cincinnati, OH, 1991. 

A corrosion mechanism similar to brass dezincification, known as dealuminification, can occur to the beta phase or eutectoid structure depending on environmental conditions. Proper quench and temper treatments produce a tempered beta structure with reprecipitated acicular alpha crystals, a combination often superior in corrosion resistance to the normal annealed structure. The nickel component in the more complex nickel aluminum bronzes alters the corrosion characteristics of the beta phase because of the nickel additive and gives greater resistance to deaUoying and cavitation-erosion in most liquids. 

Electrochemical corrosion characteristics of nickel were carried out by potentiodynamic polarization and impedance spectroscopy methods. Corrosion tests of nickel produced by electrocrystallization were ap>plied to its micrometric (Nim) and nanometric (Ni ) crystalline structures and for NiP amorphous alloy of nickel with phosphorus at content of 10.7% by weight (Eftekhari, 2008), (Kowalewska Trzaska, 2006). 

Commercial phosphoric acid contains fluorides, chlorides, sulfates, and heavy metal ions as impurities, however, which significantly increase its corrosivity and makes its corrosion characteristics unpredictable. Chloride contamination significantly increases acid corrosion of austenitic stainless steels and requires the use of nickel-based alloys. Very good corrosion behavior is reported for the superferrite XlCrNiMoNb28-4-2, Fig. 1-44 (Thyssen Edelstahl, 1979). 

Nickel metal is fairly unreactive and resistant to corrosion, characteristics that it shares with platinum and palladium. Consequently, nickel is used as an alloying metal in the production of stainless steels. Many nickel alloys are used for applications where corrosion resistance is important. For example, the alloy Monel contains 72% Ni,... 

Water environments can also have a variety of compositions and corrosion characteristics. Freshwater normally contains dissolved oxygen as well as minerals, several of which account for hardness. Seawater contains approximately 3.5% salt (predominantly sodium chloride), as well as some minerals and organic matter. Seawater is generally more corrosive than freshwater, frequently producing pitting and crevice corrosion. Cast iron, steel, aluminum, copper, brass, and some stainless steels are generally suitable for freshwater use, whereas titanium, brass, some bronzes, copper-nickel alloys, and nickel-chromium-molybdenum alloys are highly corrosion resistant in seawater. 

The highly aHoyed austenitic stainless steels are proprietary modifications of the standard AISI 316 stainless steel. These have higher creep—mpture strengths than the standard steels, yet retain the good corrosion resistance and forming characteristics of the standard austenitic stainless steels. Nickel-Base Superalloys. 

The engineering properties of electroless nickel have been summarhed (28). The Ni—P aHoy has good corrosion resistance, lubricity, and especiaHy high hardness. This aHoy can be heat-treated to a hardness equivalent to electrolytic hard chromium [7440-47-3] (Table 2), and the lubricity is also comparable. The wear characteristics ate extremely good, especiaHy with composites of electroless nickel and silicon carbide or fluorochloropolymers. Thus the main appHcations for electroless nickel are in replacement of hard chromium (29,30). 

Nickel-iron alloys have a number of important applications that are derived from such special physical properties as their unique magnetic characteristics in the regions of 35, 50 and 80% nickel and from their abnormally low thermal expansion in the region of 36-50% nickel. Although not specifically used as corrosion-resistant materials, their high resistance to attack from many common environments is of benefit in their specialised applications. 

A similar method of test was used at the International Nickel Company s Corrosion Laboratory at North Carolina. The specimen discs are mounted on insulated vertical spindles and submerged in sea-water, which is supplied continuously to the tank in which the specimens are immersed. The maximum peripheral speed of the spinning disc is about 760cms , and the characteristic pattern of attack is shown in Fig. 19.3a. Studies of variation of depth of attack with velocity indicate that at low velocities (up to about 450 cm s ) alloys such as Admiralty brass, Cu-lONi and cupro-nickel alloys containing iron maintain their protective film with a consequent small and similar depth of attack for the diflferent alloys. At higher velocities the rate increases due to breakdown of the film. 

Most published work has focused on the deposition of Ni, Co, and NiCo alloys from hypophosphite electrolytes [14], and this part of the review will deal primarily with these alloys. Other Co alloys studied include CoZnP [15, 16], the recording characteristics of which were described by Soraya [17] CoSnP [18], which is reported to have enhanced corrosion resistance and the rhenium and manganese alloys used for vertical recording, discussed below. Other reductants, such as hydrazine [19], dimethylamine borane [20-22], pyridine borane [23], and borohydride [24, 25], can be used for the chemical deposition of nickel and cobalt, but to date there has been no significant application of these to the technology of magnetic media. 

Ferro-alloys Master alloys containing a significant amount of bon and a few elements more or less soluble in molten bon which improve properties of bon and steels. As additives they give bon and steel better characteristics (increased tensile sbength, wear resistance, corrosion resistance, etc.). For master alloy production carbothermic processes are used for large-scale ferro-sihcon, ferro-chromium, ferro-tungsten, ferro-manganese, ferro-nickel and metallothermic processes (mainly alumino and sihco-thermic) for ferro-titanium, ferro-vanadium, ferro-molybdenum, ferro-boron. 

Dura nickel. Trademark of DuPont Co for a wrought, age-hardenable alloy oontg ca 94% of Ni. Has greater strength and hardness and high resistance to corrosion which is characteristic of Ni Ref CondChemDict (1961), p425... 

The deposit of nickel on top of the copper provides the essential resistance of the system to corrosion. Generally it is deposited from a solution based on the familiar Watts formulation—300 g 1 1 nickel sulphate, 30 g 1 1 nickel chloride, and 40 g 1 1 boric acid—and as in the copper processes the solutions contain additives to help give a bright deposit with good levelling characteristics. 

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