Alkalis nickel-iron alloys

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.)... 

W. Schendler, W. Schwenk, Electrochemical studies of the corrosion of heat-resistant iron and nickel-base alloys in eutectic alkali sulfate melt at 700 °C, Werkst. Korros. 32 (1981) 428—434. 

Metals such as aluminum, tin, and zinc and their alloys are unstable in NaOH solutions since they spontaneously form oxyanions of the type MOj, where M is Al, Sn, or Zn. Nickel, iron, and their alloys are more stable and are widely used in caustic service in the chlor-alkali industry. 

Nickel increases corrosion resistance by the formation of protective oxide films on the surfaces of the castings. Up to 4% Ni is added in combination with chromium to improve both strength and corrosion resistance in cast iron alloys. The enhanced hardness and corrosion resistance obtained is particularly important for improving the erosion-corrosion resistance of the material. Nickel additions enhance the corrosion resistance of cast irons to reducing acids and alkalies. Nickel additions of 12% or greater are necessary to optimize the corrosion resistance of cast irons. 

There are, however, two characteristics, ready oxidation at high temperatures and, in the case of molybdenum and tungsten, brittleness at low temperatures, which limit their applications. Of the refractory metals, tantalum has the widest use in the chemical process industries. Most applications involve acid solutions that cannot be handled with iron or nickel-base alloys. Tantalum, however, is not suitable for hot alkalis, sulfur trioxide, or fluorine. Hydrogen will readily be absorbed by tantalum to form a brittle hydride. This is also true of titanium and zirconium. Tantalum is often used as a cladding metal. 

NH4CI is acidic in aqueous solution the pH of 1%, 3%, and 10% solution at 25°C are 5.5, 5.1 and 5.0, respectively. (Merck 1996. The Merck Index, 12th ed. Rahway, NJ Merck Co.) It loses ammonia and becomes more acidic on prolonged exposure or storage. It reacts with iron, copper, nickel and other metals and some of their alloys such as bronze and brass. It reacts with alkalies forming NH3. 

Nickel is used throughout industry because of its excellent corrosion resistance. In addition to itr+us37- oe/oe" nn< cladding material to provide corrosion resistance to tanks and production vessel surfaces, nickel is used as an alloying element in steel production. Nickel is resistant to attack by NaOH and other alkali solutions, but is not compatible with ammonium hydroxide. Nickel is resistant to corrosion by sodium chloride solutions, but is corroded severely by iron, copper- and mercury chloride salts. Also, nickel has excellent corrosion resistance to most organic acids. Some of the common nickel alloys are described below ... 

Rubidium metal alloys with the other alkali metals, the alkaline-earth metals, antimony, bismuth, gold, and mercury. Rubidium forms double halide salts with antimony, bismuth, cadmium, cobalt, copper, iron, lead, manganese, mercury, nickel, thorium, and zinc. These complexes are generally water insoluble and not hygroscopic. The soluble rubidium compounds are acetate, bromide, carbonate, chloride, chromate, fluoride, formate, hydroxide, iodide,... 

Following the development of sponge-metal nickel catalysts by alkali leaching of Ni-Al alloys by Raney, other alloy systems were considered. These include iron [4], cobalt [5], copper [6], platinum [7], ruthenium [8], and palladium [9]. Small amounts of a third metal such as chromium [10], molybdenum [11], or zinc [12] have been added to the binary alloy to promote catalyst activity. The two most common skeletal metal catalysts currently in use are nickel and copper in unpromoted or promoted forms. Skeletal copper is less active and more selective than skeletal nickel in hydrogenation reactions. It also finds use in the selective hydrolysis of nitriles [13]. This chapter is therefore mainly concerned with the preparation, properties and applications of promoted and unpromoted skeletal nickel and skeletal copper catalysts which are produced by the selective leaching of aluminum from binary or ternary alloys. 

Iron-nickel alloys tend to be of lower corrosion resistance than iron-chromium alloys except towards attack by hot concentrated alkalis. Iron-chromium-nickel alloys are superior to either of the above and are resistant to alkaline and neutral aqueous solutions, atmospheric and seawater attack. Hot non-oxidising acids will cause corrosion, the rate depending on concentration and temperature. 

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). 

Hydrochloric acid as a hydrolyzer and as a product of hydrolysis in the absence of alkali has been the source of much trouble as it is one of the most corrosive chemicals known. However, even at slightly elevated temperatures, completely dry hydrogen chloride gas has very little corrosive action and is easily handled in iron equipment. Nickel and Monel metal are fairly resistant to low hydrochloric acid concentrations. With dilute acid,. several of the copper-base alloys, si ch as phosphor bronze, aluminum bronze, manganese bronze, ahd Everdur metal, have fairly good... 

Their use in the laboratory is well known. Very pure iron (e.g., carbonyl iron) and pure nickel, and sometimes also high-grade alloy steels, serve as crucible and boat materials. In particular, they are resistant to liquid and gaseous alkali and alkaline earth metals at high temperatures. 

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