Marine atmospheres

The relative susceptibHity of several commercial aHoys is presented in Table 8. The index used is a relative rating based on integrating performance in various environments. These environments include the harsh condition of exposure to moist ammonia, Hght-to-moderate industrial atmospheres, marine atmosphere, and an accelerated test in Mattsson s solution. The latter testing is described in ASTM G30 and G37 (35,36) and is intended to simulate industrial atmospheres. The index is linear. A rating of 1000 relates to the most susceptible and zero designates immunity to stress corrosion. 

The colleetion and storing of abiotic and biotic samples from different environments (atmospheric, marine and terrestrial eeosystems) was begun systematically during the austral summer in 1994-1995. 

Simoneit, B. R. T. and Elias, V. O., Detecting organic tracers from biomass burning in the atmosphere. Marine Pollut. Bull., 42, 805-810, 2001. 

Souske, R. (1962). Les toitures en zinc et les teles galvanisees en atmosphere marin (Zinc roofing and galvanized sheets in a marine atmosphere). Corros. Anticorros. 70(3), 93-96 (in French). 

Marine. Fine windswept chloride particles that get deposited on surfaces characterize this type of atmosphere. Marine atmospheres are usually highly corrosive, and the corrosivity tends to be significantly dependent on wind direction, wind speed, and distance from the coast. It should be noted that an equivalently corrosive environment is created by the use of deicing salts on the roads of many cold regions of the planet. 

Lasehermes M., Tenue des alliages d aluminium en atmosphere marine. Revue de VAluminium,... 

Guilhaudis A., Comportement de raluminium anodise en atmosphere marine, Corference du Centre de recherches et d etudes,oceanographiques. La Rochelle, 1965, p. 333-345. 

A study in the tropical Atlantic by Williams et al. involved measuring acetone, methanol, acetonitrile and dimethyl sulfide within the atmospheric marine boundary layer and the upper ocean [116]. Measurements were taken on either side of the intertropical convergence zone. This zone, which sailors commonly refer to as the doldrums, is an area around the equator where the southeast and northeast trade winds meet. Consequently, it is a natural barrier to atmospheric mixing between the hemispheres. This results in hemispheric gradients for VOCs whose atmospheric lifetimes are shorter than interhemispheric mixing times... 

The visbreaking process thermally cracks atmospheric or vacuum residues. Conversion is limited by specifications for marine or Industrial fuel-oil stability and by the formation of coke deposits in equipment such as heaters and exchangers. 

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. 

The importance of ozone in the stratosphere has been stressed in Section 9.3.8. The fact that ozone can be decomposed by the halogen monoxides CIO, BrO and 10 means that their presence in the stratosphere contributes to the depletion of the ozone layer. For example, iodine, in the form of methyl iodide, is released into the atmosphere by marine algae and is readily photolysed, by radiation from the sun, to produce iodine atoms which can react with ozone to produce 10 ... 

Galvalume has been shown to have two to six times the life of an equivalent thickness of 2inc, including marine atmospheres. Eor high temperature oxidation resistance up to 700°C, Galvalume is equivalent to pure aluminum. 

Tin—cadmium coatings are particularly resistant to marine atmospheres and have appHcations in the aviation industry. 

Many components of ships and marine stmctures are now coated in the shop under controlled conditions to reduce the amount of solvents released into the atmosphere, improve the quaUty of work, and reduce cost. Regulations designed to limit the release of volatile organic compounds into the air confine methods of shop apphcation to those having transfer efficiencies of 65%. Transfer efficiency is defined as the percent of the mass or volume of sohd coating that is actually deposited on the item being coated, and is calculated as... 

Corrosion. Copper and selected copper aHoys perform admirably in many hostile environments. Copper aHoys with the appropriate corrosion resistance characteristics are recommended for atmospheric exposure (architectural and builder s hardware), for use in fresh water supply (plumbing lines and fittings), in marine appHcations (desalination equipment and biofouling avoidance), for industrial and chemical plant equipment (heat exchangers and condensers), and for electrical/electronic appHcations (coimectors and semiconductor package lead-frames) (30) (see Packaging). 

The reproducibility of test results between labs using the neutral salt spray tests has not been consistent, but the repeatability, within one lab, is better, and the test has value in comparing variations in coating systems. Correlation of hours of exposure in the salt spray test to actual performance of the plated part in service, even in marine atmospheres, is not consistent and usually avoided. A classic example is that cadmium deposits outlast zinc deposits on steel in salt spray tests and clean marine atmospheres, yet zinc outlasts cadmium when exposed to real, industrial atmospheres, because of the presence of sulfur-bearing corrodents in industrial environments. An important variable in salt spray testing is the position of the surface to be tested. Whereas the surface of test panels is specified to be 15—30° from the vertical (40), when salt spray testing chromated zinc-plated specimens, this range has appeared excessive (41). 

Tin—Nickel. AHoy deposits having 65% fin have been commercially plated siace about 1951 (135). The 65% fin alloy exhibits good resistance to chemical attack, staining, and atmospheric corrosion, especially when plated copper or bron2e undercoats are used. This alloy has a low coefficient of friction. Deposits are solderable, hard (650—710 HV ), act as etch resists, and find use ia pfinted circuit boards, watch parts, and as a substitute for chromium ia some apphcafions. The rose-pink color of 65% fin is attractive. In marine exposure, tin—nickel is about equal to nickel—chromium deposits, but has been found to be superior ia some iadustfial exposure sites. Chromium topcoats iacrease the protection further. Tia-nickel deposits are bfitde and difficult to strip from steel. Temperature of deposits should be kept below 300°C. 

Figure 5 Schematic illustration of the sources and sinks of DMS in the marine boundary layer of the atmosphere and the oceanic mixed layer (Taken from Bigg," with permission of Cambridge University Press)...

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