Resistant to atmospheric corrosion

Atmospheric corrosion results from a metal s ambient-temperature reaction, with the earth s atmosphere as the corrosive environment. Atmospheric corrosion is electrochemical in nature, but differs from corrosion in aqueous solutions in that the electrochemical reactions occur under very thin layers of electrolyte on the metal surface. This influences the amount of oxygen present on the metal surface, since diffusion of oxygen from the atmosphere/electrolyte solution interface to the solution/metal interface is rapid. Atmospheric corrosion rates of metals are strongly influenced by moisture, temperature and presence of contaminants (e.g., NaCl, SO2,. ..). Hence, significantly different resistances to atmospheric corrosion are observed depending on the geographical location, whether mral, urban or marine. 

Excellent resistance to saltwater corrosion and biofouling are notable attributes of copper and its dilute alloys. High resistance to atmospheric corrosion and stress corrosion cracking, combined with high conductivity, favor use in electrical/electronic appHcations. 

It is agreed generally that the characteristics of the rust films that form on steels determine their resistance to atmospheric corrosion. The rust films that form on low-aUoy steels are more protec tive than those that form on unalloyed steel. 

In the massive state none of these elements is particularly reactive and they are indeed very resistant to atmospheric corrosion at normal temperatures. However, nickel tarnishes when heated in air and is actually pyrophoric if very finely divided (finely divided Ni catalysts should therefore be handled with care). Palladium will also form a film of oxide if heated in air. 

From the work described and other investigations , it is evident that copper and most copper alloys are highly resistant to atmospheric corrosion. In general, copper itself is as good as, or better than, any of the alloys. Some of the brasses are liable to suffer rather severe dezincification and it is unwise to expose these to the more corrosive atmospheres without applying some protection. 

Chromium is highly resistant to atmospheric corrosion, being almost inert in most atmospheres, and is therefore used as a thin, bright overlay to other... 

The corrosion resistance of zinc is discussed in Section 4.7, and it is only necessary here to say that zinc is protected against further attack by a film of corrosion products. It is remarkably resistant to atmospheric corrosion except perhaps in the most heavily contaminated industrial areas, and even there its use as a protective coating is still a sound practical and economic proposition. The value of zinc coatings as a basis for painting under very aggressive conditions has been clearly demonstrated. 

Uses.—Palladium is seldom used in the pure state, and its alloys have hitherto received but little application even in scientific work, although recently a useful field has been discovered for utilising certain alloys, such as those of palladium and gold, as substitutes for platinum. They have been used, on account of their excellent resistance to atmospheric corrosion, for certain astronomical and dental purposes, and for coating the surfaces of reflectors used for searchlights, etc. Palladium salts are used in photography. 

Sb and Cu. Its resistance to atmospheric corrosion and to attack by acids leads to employment in chemiceil plant, for pipes and cable sheathing. The presence of 0.050—0.065% of tellurium improves the properties desirable for thes(i purposes, such as grain-size, hardness, tensile strength and corrosion resistance. Alloyed with a little Sb, it is used in large quantities for the electrode grids in lead-acid storage batteries. 

Properties Distinctive reddish color. D 8.96, mp 1083C, bp 2595C. Ductile, excellent conductor of electricity. Complexing agent, coordination numbers 2 and 4. Dissolves readily in nitric and hot concentrated sulfuric acids in hydrochloric and dilute sulfuric acids slowly, but only when exposed to the atmosphere. More resistant to atmospheric corrosion than iron, forming a green layer of hydrated basic carbonate. Readily attacked by alkalies. A necessary trace element in human diet, and a factor in plant metabolism. Essentially nontoxic in elemental form. Noncombustible, except as powder. 

Red brasses are widely used for decorative purposes and in plumbing and piping because of their resistance to atmospheric corrosion and dezincification. 

Small additions of copper to steel render it more resistant to atmospheric corrosion. 

Although it readily combines with oxygen, aluminium is resistant to atmospheric corrosion because a thin film of closely adherent oxide is formed which protects the underlying metal from attack. Aluminium powder is therefore used as a pigment in anticorrosive paints. 

CHEMICAL PROPERTIES stable in air stable under ordinary conditions of use and storage hazardous polymerization will not occur more resistant to atmospheric corrosion than iron readily attacked by dilute nitric acid, hot concentrated sulfuric acid, and hydrobro-mic acid very slowly attacked by cold hydrochloric acid and dilute sulfuric acid also attacked by acetic and other organic acids excellent conductor of electricity a complexing agent FP (NA) LFL/UFL (NA) AT (NA) Hf (13.26 kJ/mol at 1357.77K) RES (1.673 microohm/cm). 

High mechanical and electrical resistance, wide operation temperature range (from 260 toi - -260°C), low friction coefficient. Surpasses all known materials in chemical resistance. Resistant to atmospheric, corrosion and radiation effects. 

Chromium and aluminum are resistant to atmospheric corrosion individually but when porous chromium in intimate contact with aluminum is exposed to high humidities substantial corrosion occurs at the interface of the two materials. This is illustrated by the roughening data of Figure 4. Auger electron spectroscopy shows 0, S,... 

Copper and copper alloys are highly resistant to atmospheric corrosion because of surface films mainly composed of basic copper salts. The corrosion rate is below 2-3 pm/year [8.9]. Tin as well as nickel and nickel alloys also corrode at similar rates. Lead possesses excellent corrosion resistance in atmospheres due to surface-protecting films (insoluble sulphate, sulphide, carbonate and oxide). 

Common product forms, tensile strength, and resistance to atmospheric corrosion of some wrought aluminium materials are shown in Table 10.11. The strongest grades of the various alloys imply lower ductility, i.e. elongation mainly within the range 2-12%, compared to 15-35% for the softest grades. A number of fields of application of the same materials are listed in Table 10.12. 

It Is a very good conductor, is non-magnetic and offers considerable resistance to atmospheric corrosion. Copper toughens with work, but may be annealed, or softened, by heating to dull red before quenching. 

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