Outdoor atmospheres

Air contaminants Aerosols, gases, vapors or dusts which may cause adverse effects if discharged into the indoor or outdoor atmosphere. 

Nickel and nickel alloys do not form thick layers of corrosion products when freely exposed to outdoor atmospheres in circumstances where the surface is periodically washed by rain, but such deposits may form on sheltered surfaces. Quantitative data on the rate of loss of metal and of pitting of nickel and nickel alloys exposed to outdoor atmospheres are avail-able . Figure 4.38 shows results obtained at three sites in the USA over a 7 year period and Fig. 4.39 gives results from a 10 year test at Birmingham. In both series of tests, Ni-Cr-Fe alloys gave lower weight losses than nickel itself or Ni-Cu alloys and the American results bring out the... 

Vernon claims that in outdoor atmospheres the corrosion product consists largely of zinc oxide, hydroxide and combined water, but also contains zinc sulphide, zinc sulphate and carbonate. The following table gives the composition of typical films formed in an industrial atmosphere. 

Tantalum has a high resistance to general outdoor atmospheres. Tantalum and the Ta-lOW alloy are virtually immune to sea water at ambient conditions and tantalum is only tarnished in oxygenated sea water at 26°C. 

The deposit resists atmospheric tarnish even in the presence of high pollution by sulphur dioxide (in contrast to nickel) and hydrogen sulphide, and coatings exposed to the outdoor atmosphere remain bright indefinitely, sometimes taking on a slightly more pink colour as the oxide film thickens. 

L. Veleva, M. A. Alpuches-Aviles, Outdoor atmospheric corrosion, ASTM, STP 1421, H.E. Townsend, Ed. American Society for Testing and Materials International, West Conshochoken, PA, 2002. 

A number of studies have documented that concentrations of some of the directly emitted species found in outdoor atmospheres can be quite high indoors if there are emission sources present such as combustion heaters, gas stoves, or tobacco smoke. In addition, there is evidence for chemistry analogous to that occurring outdoors taking place in indoor air environments, with modifications for different light intensities and wavelength distributions, shorter residence times, and different relative concentrations of reactants. In Chapter 15, we briefly summarize what is known about the chemical composition and chemistry of indoor atmospheres. 

Indoor environments usually have lower concentrations of the outdoor pollutants than the outdoor atmosphere as many museums are equipped with air conditioning and various filtration systems, and of course additionally indoor surfaces (including artifacts) can act as reaction sites and sinks of pollutants by virtue of reaction and adsorption processes. 

Corrosion rate data obtained in various outdoor atmospheres given in Table 4.66 show a range of values (0.03-0.61 mdd or 0.004-0.0077 mpy). The general trend involves decreasing corrosion rate with increasing duration. 

Materials such as metals, alloys, steels and plastics form the theme of the fourth chapter. The behavior and use of cast irons, low alloy carbon steels and their application in atmospheric corrosion, fresh waters, seawater and soils are presented. This is followed by a discussion of stainless steels, martensitic steels and duplex steels and their behavior in various media. Aluminum and its alloys and their corrosion behavior in acids, fresh water, seawater, outdoor atmospheres and soils, copper and its alloys and their corrosion resistance in various media, nickel and its alloys and their corrosion behavior in various industrial environments, titanium and its alloys and their performance in various chemical environments, cobalt alloys and their applications, corrosion behavior of lead and its alloys, magnesium and its alloys together with their corrosion behavior, zinc and its alloys, along with their corrosion behavior, zirconium, its alloys and their corrosion behavior, tin and tin plate with their applications in atmospheric corrosion are discussed. The final part of the chapter concerns refractories and ceramics and polymeric materials and their application in various corrosive media. 

Atmospheric pollution cannot be controlled so long as the nature and the mechanism of formation of its deleterious constituents remain unknown. While many chemical constituents of polluted atmospheres have been identified, their presence or concentration does not seem to follow a regular pattern. On the other hand, ozone is always present in polluted outdoor atmospheres. Its concentration consistently rises from a normal value of a few parts per hundred million to many times this value during periods of severe contamination. Whether ozone is the primary cause of pollution or is a secondary effect of the reaction of other substances is not entirely clear, but it appears to be an important link in the chain of chemical reactions which produce atmospheric pollution. Very likely, a knowledge of the variations of ozone concentration in atmospheres would permit a study of the influence of the various parameters, and this knowledge may eventually furnish a lead to an explanation of the mechanism of formation and the effects of pollutants. 

Pervasive air pollutants. Those air pollutants that are present in the general outdoor atmosphere to which all individuals will be exposed. These result from releases of toxicants into the air and from chemical reactions that take place in the atmosphere. 

The legal definition of air pollution is the presence in the outdoor atmosphere of any one or more substances in quantities, which may or are harmful/injurious to human health or welfare, animal or plant life, or property, or interfere with the enjoyment of life, property or outdoor activity. ... 

Air pollution is usually defined as the presence in the outdoor atmosphere, of substances put there directly or indirectly by an act of man, in amounts which are detrimental to health and safety or interfere with the fulJ jise of materials or property, e.g. made from polymeric materials. Man is not the only agent able to pollute the atmosphere. There are many natural processes that do so such as pollination of plants, volcanic emptions, dust stormes and forest fires. There are also secondary pollutants in the atmosphere, formed in the air from primary pollutants, due to acts by man, e.g. smoke, industrial pollutants and photochemical smog formed in the air from substances emitted from automobile exhaust and other sources. 

In outdoor atmospheres dry deposition of S-pol-lutants and especially of S0 is of greatest importance. Dose response functions describing corrosion as function of SOp and time of wetness are available for some materrals as steel and zinc. 

According to the present knowledge NO has only limited influence on corrosion of steel and zinc in outdoor atmospheres, there are however indications that NO in combination with SO2 promote corrosion of e.g. copper. 

Experimental tests in the outdoor atmosphere (16) (simulated solar collectors) found substantially higher heat transfer coefficients than predicted by laminar theory or than measured in a wind tunnel, presumably because of the higher turbulence levels encountered. The relationship was approximately... 

Because of their double bonds, isoprene and a-pinene are Ukely to react with ozone (Weschler and Shields, 1999). These reactions may cause a difference between indoor and outdoor atmospheric chemistry, since these compounds have known indoor sources. An important product from these reactions may be the far more reactive OH- radical (Atkinson et al., 1992 Weschler and Shields, 1996). 

In many cases, the spread of environmental contaminants is related to air pollution. The first incidence of air pollution is lost in unrecorded history, but it certainly goes back to the time of the discovery of fire. Air pollution refers to the presence in the outdoor atmosphere of one or more contaminants, occurring in quantities, of a duration, and with characteristics that are known to be injurious to human, animal, and plant life, or to property,... 

Soil-derived partieles sueh as aluminosilicates, CaCOs, and Si02 are the seeond most abundant partiele type in indoor environment of subway stations. The relative abundanee of the sod-derived particles in subway stations are the lowest in the tunnel and the highest at the waiting room. Also secondary particles sueh as nitrates and sulfates are more abundantly encountered in the waiting room than in the platform area. The soil-derived and secondary aerosol particles are likely from the outdoor atmosphere. Therefore, the contents of those particles are higher for the samples eoUeeted at the loeations closer to the outdoor. 

ISO CORRAG [23], the International Organization for Standardization (ISO) has implemented a classification system for evaluating atmospheric corrosivity and on the basis of variables that are fairly easy to obtain [24, 25]. This ISO classification has found several applications, for example, to predict the long-term corrosion behavior in different environments and to evaluate the effect of protective coatings. It contains two principally different approaches of assessing the corrosivity of any outdoor atmospheric environment. The first is based on exposure of standard specimens of steel, copper, zinc, and aluminum for one year whereby the corrosion effect is measured through mass loss measurements. One of five measured corrosivity classes... 

In wet atmospheres, nickel initially forms NiO and (NiOH)2 [35,36]. Nickel sulfates are present as corrosion products on the surface in outdoor exposures [37].Jouenefatmospheric corrosion of nickel in industrial, urban, and rural atmospheres. Nickel corrodes through a pitting corrosion process. The highest corrosion rates were observed in industrial areas. The corrosion products were mainly sulfates, chlorides, and n ligible amounts of nitrates surrounded by carbonate species. The pitting corrosion process occurs in two steps on nickel surfaces exposed to an outdoor atmosphere, as shown in Fig. 10.9 [38]. 

Fig. 10.9 Schematic of the pitting corrosion process occurring on nickel surfaces exposed in outdoor atmospheres (a) pitting corrosion process and (b) formation of corrosion products [38].

For a typical outdoor atmosphere, C is of the order of 10 mg/L, and the second term in Eq. (10.32) is then dominant for values of (pr greater than about 10" s that is, at temperatures more than 25°C above Tg (Gent and McGrath, 1965). 

H. H. Lawson, Outdoor atmospheres, in Corrosion Tests and Standards Application and Interpretation, 2nd edition, R. Baboian, editor, ASTM International, West Conshohocken, 2005, pp. 343-348. 

Apart from oxygen, all unsaturated elastomers are also susceptible to ozone attack, although ozone concentration in the outdoor atmosphere at ground level is... 

Townsend, H.E. Estimating the atmospheric corrosion resistance of weathering steels in outdoor atmospheric corrosion, STP 1421, pp. 292-300. ASTM, West Conshohocken (2002)... 

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