Acids nickel-iron alloys

Much of the information available on resistance of nickel-iron alloys to corrosion by mineral acids is summarised by Marsh. In general, corrosion rates decrease sharply as the nickel content is increased from 0 to 30-40%, with little further improvement above this level. The value of the nickel addition is most pronounced in conditions where hydrogen evolution is the major cathodic reaction, i.e. under conditions of low aeration and agitation. Results reported by Hatfield show that the rates of attack of Fe-25Ni alloy in sulphuric and hydrochloric acid solutions, although much lower than those of mild steel, are still appreciable (Tables 3.35 and 3.36). In solutions of nitric acid, nickel-iron alloys show very high rates of corrosion. 

Heat treatment, e.g. 2 h at 600°C, improves the resistance to corrosion of nickel-boron and nickel-phosphorus electroless nickel deposits, especially to acid media. This presumably results from formation of a nickel-iron alloy layer . 

Hydrochloric acid (HCl) has a variety of effects on the corrosion of titanium-nickel alloys depending on temperature, acid concentration, and specific alloy composition. With 3% HCl at 100 C (212 F) and a range of alloy compositions, the rate of attack was as low as 0.36 mpy and as high as 3.3 mpy. At 25 °C (77 °F) and 7M solution, titanium-nickel-iron alloys can lose up to 457 mpy. 

The composition of this alloy (54% nickel, 15% molybdenum, 15% chromium, 5% tungsten and 5% iron) is less susceptible to intergranular corrosion at welds. The presence of chromium in this alloy gives it better resistance to oxidizing conditions than the nickel/molybdenum alloy, particularly for durability in wet chlorine and concentrated hypochlorite solutions, and has many applications in chlorination processes. In cases in which hydrochloric and sulfuric acid solutions contain oxidizing agents such as ferric and cupric ions, it is better to use the nickel/molybdenum/ chromium alloy than the nickel/molybdenum alloy. 

Nickel/silicon alloy (10% silicon, 3% copper, and 87% nickel) is fabricated only as castings and is rather brittle, although it is superior to the iron/silicon alloy with respect to strength and resistance to thermal and mechanical shock. It is comparable to the iron/silicon alloy in corrosion resistance to boiling sulfuric acid solutions at concentrations above 60%. Therefore, it is chosen for this and other arduous duties where its resistance to thermal shock justifies its much higher price compared with iron/silicon alloys. 

Replacing some of the nickel with iron produces a family of alltws with intermediate corrosion resistance between stainless steels and the Ni-Cr-Mo alloys. Alloys such as Incoloy 825 and Hastelloy G-3 and G-30 are in this family. Incoloy 825 has 40 percent Ni, 21 percent Cr, 3 percent Mo, and 2.25 percent Cu. Hastelloy G-3 contains 44 percent Ni, 22 percent Cr, 6.5 percent Mo, and 0.05 percent C maximum. These alloys have extensive applications in sulfuric acid systems. Because of their increased nickel and molybdenum contents they are more tolerant of chloride-ion contamination than are standard stainless steels. The nickel content decreases the risk of stress-corrosion cracking molybdenum improves resistance to crevice corrosion and pitting. Many of the nickel-based alloys are proprietary and are coverecf by the following specifications ... 

The trade name Hastelloy covers a range of nickel, chromium, molybdenum, iron alloys that were developed for corrosion resistance to strong mineral acids, particularly HC1. The corrosion resistance, and use, of the two main grades, Hastelloy B (65 per cent Ni, 28 per cent Mo, 6 per cent Fe) and Hastelloy C (54 per cent Ni, 17 per cent Mo, 15 per cent Cr, 5 per cent Fe), are discussed in papers by Weisert (1952a,b). 

Nitration reactions are carried out in closed vessels that are provided with an agitating mechanism and means for controlling the reaction temperature. The nitration vessels are usually constructed of cast iron and steel, but often acid-resistant alloys, particularly chrome-nickel steel alloys, are used. 

Sulphuric acid concentration, performed in two steps, requires eight heat exchangers, one pump and a knockout drum. A nickel-iron-chromium alloy is used for the majority of equipment and piping due to the presence of hot concentrated sulphuric acid. Capital investment of this section is about EUR(08) 57.3 M (it includes tanks for sulphuric acid). 

Concentrated sulphur acid evaporation and dehydration is performed in a group of two heat exchangers with important exchange surface (up to 1 340 m2) (HX-208). The S03/S02 decomposition reactor (HX-209) is a set of five reactors with two reactive zones. The first one, with a temperature of 875 K requires a platinum catalyst and the second one an iron-oxide catalyst. The operating temperature in the second zone increases up to 1125 K. Due to operating conditions (temperature, chemical composition), these three devices require a nickel-iron-chromium alloy. Then sulphur trioxide recombination reactor consists of a packed column (HX-210). Required investment for S03 conversion is estimated about EUR(08) 508.6 M. 

Nickel and its common alloys such as Monel (nickel-copper), Inconel (nickel-iron-chromium), and Duranickel (primarily nickel) can be bonded with procedures that are recommended for stainless steels.35 A simple nitric acid process has also been used consisting of solvent cleaning, immersion for 4 to 6 s at room temperature in concentrated nitric acid, rinsing with cold deionized water, and finally drying. Also, a chromium trioxide-hydrochloric acid process consisting of a 60- to 80-s immersion in acid solution has been suggested. If immersion is impossible, this latter solution may be applied with a cheesecloth after solvent cleaning. The solution is applied to approximately 1 ft2 of the substrate surface at a time, and it remains on the part for approximately 1 min. 

In recent years, a number of especially resistant iron alloys have appeared on the market and have been rapidly adopted. They are, essentially, nickel-chrome-iron alloys, usually containing very little carbon. These alloys are very resistant to acids and alkalis and are used chiefly where high resistance to chemicals is the deciding factor. The different VA-steels, and the English S-80, are examples of these alloys which vary in composition depending on the particular application. These alloys withstand concentrated nitric acid, and other acids, except hydrochloric, scarcely attack them at all. They are especially important in modem high pressure syntheses. Potassium hydroxide scarcely attacks these alloys even in fusion mixtures, and they are quite satisfactory, therefore, for indanthrene fusions. (Nickel is also suitable in this particular case.)... 

Frumkin and Kolotyrkin (25) have applied the concept and techniques successfully to the dissolution of lead and nickel in acids and iron in alkalies. The author (18, 26) has shown that the dissolution of aluminum in acid and alkaline solutions containing various oxidation-reduction systems behaves according to this principle. He also showed that the rate of dissolution of aluminum, zinc and their alloys in various acid, neutral, and alkaline solutions may be obtained from polarization data (27). 

The trade name Hastelloy covers a range of nickel, chromium, molybdenum iron alloys that were developed for corrosion resistance to strong mineral acids. 

From among the methods mentioned above, iron has been determined with the use of Chrome Azurol S - in waters [176], Bromopyrogallol Red - in magnetic Fe-Co-Ni films [177], sulphanilic acid - in blood plasma [129] and in plants [109], Tiron - in geological materials [114], in aluminium alloys and copper [115], 2,2 -diquinoxalyl - in niobium oxide [128], PAN - in alloys and biological samples [79] and in waste waters [178], TAN - in geological samples [83], 5-Br-PADAP - in biological samples (by derivative spectrophotometry) [91] and in copper alloys [179], and morin - in copper-chromium and nickel-chromium alloys [122]. 

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