Atmospheres, corrosive


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.  [c.2731]

Ailor W H (eds) 1982 Atmospheric Corrosion (New York Wiley)  [c.2739]

It has found application in making low-melting allows an allow of 24% indium - 76% gallium is liquid at room temperature. It is used in making bearing alloys, germanium transistors, rectifiers, thermistors, and photoconductors. It can be plated onto metal and evaporated onto glass, forming a mirror as good as that made with silver but with more resistance to atmospheric corrosion.  [c.116]

Aluminum and Aluminum Alloys. Aluminum alloys are used wherever lightness or atmospheric corrosion resistance are requited, or where mildly corrosive fluids are involved. Typical appHcations for aluminum alloys include railroad tank cars and the skin on aircraft increasingly, aluminum is being used in the automotive industry. Aluminum alloys are classified as heat-treatable or nonheat-treatable. Strengths of commercially pure and nonheat-treatable alloys are developed by strain hardening and by alloying elements of which magnesium, manganese, and silicon are typical examples. The beneficial effects of strain hardening can be erased by the heat of the welding process thus, heat inputs ate kept low when welding these aluminum alloys. The alloying elements in heat-treatable aluminum alloys are dissolved in the aluminum at high temperature by a process known as solution heat treatment subsequent heat treatment precipitates these elements as microscopic particles of intermetaUic phases, which strengthen the alloy. The welding heat dissolves these particles at or neat the weld, thus reducing the strength properties can be restored by a post-weld heat treatment.  [c.347]

Some other steels that faU into related categories are the various long-standing proprietary weathering steels, eg, USS s Cor-Ten A, which uses small amounts of copper and phosphoms to improve atmospheric corrosion resistance. These elements also produce significant soHd solution hardening. Phosphoms is also used for its strengthening effects alone, although the toughness is degraded.  [c.396]

Elemental copper is resistant to aerated alkaline solutions except in the presence of ammonia. Copper does not displace hydrogen from acid but dissolves readily in oxidising acids such as nitric acid (qv) or in acid solutions that contain an oxidising agent, such as sulfuric acid solution containing ferric sulfate. Because of corrosion resistance to salt solutions, copper is used in marine appHcations (see Coatings, marine Corrosion and corrosion control). Resistance to oxidation by water vapor at high temperatures has made copper a material of choice in cooling systems. Although the surface of copper oxidizes on exposure to the atmosphere, further corrosion is inhibited by the formation of a tightly adherent protective coating of corrosion products. In many instances this takes the form of a green patina that imparts a rich appearance to architectural and artistic uses. Studies of the chemistry of atmospheric corrosion have shown that the initial attack on copper metal involves the formation of sulfides and oxides. Upon further oxidation and reaction with water, basic copper sulfates, such as CuSO Cu(OH)2 and CuSO 3Cu(OH)2, are formed. The latter compound is found in nature as the mineral brochantite. A basic carbonate, CuCO Cu(OH)2, may also be present in some deposits (15).  [c.195]

Atmospheric exposure, fresh and salt waters, and many types of soil can cause uniform corrosion of copper aHoys. The relative ranking of aHoys for resistance to general corrosion depends strongly on environment and is relatively independent of temper. Atmospheric corrosion, the least damaging of the various forms of corrosion, is generaHy predictable from weight loss data obtained from exposure to various environments (31) (see Corrosion and CORROSION CONTKOL).  [c.226]

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.  [c.230]

Lead and Lead—Tin Alloys. Lead is plated from fluoborate solutions, as shown in Table 13. Lead is used in battery parts for its good resistance to sulfuric acid (see Batteries). Low tin alloys of lead are used in bearings 93% lead—7% tin was specified for bearings on piston aircraft engines. Lead—tin alloys of 3—15% tin are called teme for hot-dip coatings, temeplate can be 20% tin. Temeplate has been used to protect steel in gasoline tanks. Solder deposits are also plated. Lead—tin baths are similar to lead baths. Staimous fluoborate is added to supply the tin. Sulfamate solutions have been described for lead plating (108,109), but have found Httle industrial use. Requirements for lead and lead—tin deposits on steel are specified (110). These deposits have outstanding resistance to atmospheric corrosion, especially with a 0.25 pm copper strike undercoat. Lead coatings (19 pm) show an expected life of more than nine years in an industrial atmosphere. Up to 15% tin does not decrease the corrosion resistance. Newer baths based on methane sulfonic acid are gaining in use both for lead (qv) and lead—alloy (see Lead alloys) baths. Lead is under strict regulation in the environment and waste streams. The future of lead plating is uncertain.  [c.160]

Atmospheric corrosion. Air-cooled heat exchangers should not be located where corrosive vapors and fumes from vent stacks will pass through them.  [c.1081]

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.  [c.2422]

With some important exceptions, gray-iron castings generally have corrosion resistance similar to that of carbon steel. They do resist atmospheric corrosion as well as attack by natural or neutral waters and neutral soils. However, dilute acids and acid-salt solutions will attack this material.  [c.2443]

Mild steel, also low-alloy irons and steels 0 3 0 3 < 400 1 < 750 Wronglit, cast Good Good 67 6.7 Higli strengths obtainable by alloying, also improved atmospheric corrosion resistance. See ASTM specifications for particular grade  [c.2446]

A frequently cited example of protection from atmospheric corrosion is the Eiffel Tower. The narrow and, for that age, thin sections required a good priming of red lead for protection against corrosion. The top coat was linseed oil with white lead, and later coatings of ochre, iron oxide, and micaceous iron oxide were added. Since its constmction the coating has been renewed several times [29]. Modern atmospheric corrosion protection uses quick-drying nitrocellulose, synthetic resins, and reaction resins (two-component mixes). The chemist Leo Baekeland discovered the synthetic material named after him, Bakelite, in 1907. Three years later the first synthetic resin (phenol formaldehyde) proved itself in a protective paint. A new materials era had dawned.  [c.9]

Data from H. R. Copson, Report of ASTM Subcommittee VI, of Committee B-3 on Atmospheric Corrosion, Am. Soc. Test Mater., Spec. Tech. Publ. 175, 1955. Used by permission of the American Society for Testing and Materials, Philadelphia.  [c.128]

The consumption of oxygen due to atmospheric corrosion of sealed metal tanks may cause a hazard, due to oxygen-deficiency affecting persons on entry.  [c.55]

Critical Humidity—the relative humidity (RH) at and above which the atmospheric corrosion rate of a metal increases significantly.  [c.47]

Sprayed aluminum coatings used on steel for protection against atmospheric corrosion are preferred over zinc for use in areas with considerable contamination of the atmosphere by sulfur oxides [44]. Sprayed aluminum also is used for the protection of steel at elevated temperatures up to 550 C. For temperatures of 550-900°C, aluminum is converted to a high-melting point aluminum/iron compound by heating the coated equipment to 800/900 C and maintaining it at that temperature for 15 minutes. For protection up to 1000°C, a sprayed coating of nickel chromium and nickel and cobalt alloys is applied. Nickel or cobalt alloys containing small amounts of boron or silicon can be deposited with very simple equipment, requiring very little heating of the base metal.  [c.100]

Zinc diffusion is used for protection against atmospheric corrosion. Aluminum diffusion is used to improve the oxidation resistance of low-carbon steels.  [c.101]

Consider the failure of an unloading hose that leaks on being coupled up. For simplicity, it is assumed that the failures are caused by (1) atmospheric corrosion while the unused hose is waiting for the next unloading or (2) damage from the act of coupling. The first is clearly a time-related failure and the second a demand-related failure. A data collection system, or an analyst wanting data, would simply record the number of failures (the numerator) and the number of demands during the period of interest (the denominator). Dividing the numerator by the number of times coupling had occurred would produce the failure rate in failures per demand.  [c.14]

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.  [c.1149]

Fin material preferred from atmospheric corrosion standpoint.  [c.259]

Apply appropriate film-forming inhibitors to reduce atmospheric corrosion during storage and transit.  [c.1341]

Commercially pure aluminum has good resistance to atmospheric corrosion, except where chloride is present in significant quantities, i.e. within 1-2 km of the coast and in the vicinity of chemical plants. To achieve reasonable strength, alloying additions of silicon, manganese, zinc and copper are made. Aluminum-copper alloys have poor corrosion resistance and should not be used in corrosive environments. The other aluminum alloys have good corrosion resistance to most near-neutral media but are attacked in acidic and alkaline conditions. They are susceptible to pitting corrosion, especially where deposits form. Chloride ions also induce pitting of these alloys chloride is often generated by the hydrolysis of chloride containing organic chemicals. Other organic materials can be handled safely when dry, except alcohols. Metal ions such as copper, which may be introduced by the corrosion of other plant, storage vessels or pipework, can plate out onto the aluminum and create a galvanic cell which produces intense pitting.  [c.906]

Impedance spectroscopy This technique is essentially the extension of polarization resistance measurements into low-conductivity environments, including those listed above. The technique can also be used to monitor atmospheric corrosion, corrosion under thin films of condensed liquid and the breakdown of protective paint coatings. Additionally, the method provides mechanistic data concerning the corrosion processes, which are taking place.  [c.911]

Eccentricity alters the hydraulic loading of the seal faces, reducing seal life and performance. If the shaft is eccentric to the box bore, check the slop, or looseness, in the pump bracket fits. Rust, atmospheric corrosion, or corrosion from leaking gaskets can cause damage to these fits, making it impossible to ensure a stuffing box that is concentric with the shaft. A possible remedy for this condition is welding the corroded area and re-machining to proper dimensions.  [c.952]

The classification given in Table 1.2 is based on the various forms that corrosion may take, but the terminology used in describing corrosion phenomena frequently places emphasis on the environment or cause of attack rather than the form of attack. Thus the broad classification of corrosion reactions into wet or dry is now generally accepted, and the nature of the process is frequently made more specific by the use of an adjective that indicates type or environment, e.g. concentration—cell corrosion, crevice corrosion, bimetallic corrosion and atmospheric corrosion.  [c.14]

Kucera, V. and Mattson, E., Atmospheric Corrosion of Bimetallic Structures, ex Atmospheric Corrosion, 561, J. Wiley and Sons, (1982)  [c.242]

Metals are more frequently exposed to the atmosphere than to any other corrosive environment. Atmospheric corrosion is also the oldest corrosion problem known to mankind, yet even today it is not fully understood. The principal reason for this paradox lies in the complexity of the variables which determine the kinetics of the corrosion reactions. Thus, corrosion rates vary from place to place, from hour to hour and from season to season. Equally important, this complexity makes meaningful results from laboratory experiments very difficult to obtain.  [c.335]

However, the object of this section is to outline the principles which govern atmospheric corrosion, and the emphasis is placed on metals whose atmospheric corrosion is of economic importance. These include iron and steel, zinc, copper, lead, aluminium and chromium.  [c.335]

Classification of Atmospheric Corrosion  [c.335]

Atmospheric corrosion can be conveniently classified as follows  [c.335]

However, in this section emphasis is placed upon damp and wet atmospheric corrosion which are characterised by the presence of a thin, invisible film of electrolyte solution on the metal surface (damp type) or by visible deposits of dew, rain, sea-spray, etc. (wet type). In these categories may be placed the rusting of iron and steel (both types involved), white rusting of zinc (wet type) and the formation of patinae on copper and its alloys (both types).  [c.336]

The composition given in Table 2.8 is global and, for most components, is reasonably constant for all locations, but the water vapour content will obviously vary according to the climatic region, season of the year, time of the day, etc. However, only oxygen, carbon dioxide and water vapour need to be considered in the context of atmospheric corrosion.  [c.337]

Sulphur oxides These (SO2 is the most frequently encountered oxide) are powerful stimulators of atmospheric corrosion, and for steel and particularly zinc the correlation between the level of SO2 pollution and corrosion rates is good However, in severe marine environments, notably in the case of zinc, the chloride contamination may have a higher correlation coefficient than SO2.  [c.338]

Electrochemistry of Atmospheric Corrosion  [c.344]

The double fluorides decompose at even higher temperatures to form the metal fluoride and volatile NH and HF. This reaction produces pure salts less likely to be contaminated with oxyfluorides. Beryllium fluoride [7787-49-7] from which beryllium metal is made, is produced this way (18) (see Beryllium AND BERYLLIUM alloys). In pickling of stainless steel and titanium, NH4HF2 is used with high concentrations of nitric acid to avoid hydrogen embrittlement. Ammonium bifluoride is used in acid dips for steel (qv) prior to phosphating and galvanizing, and for activation of metals before nickel plating (19,20). Ammonium bifluoride also is used in aluminum anodizing formulations. Ammonium bifluoride is used in treatments to provide corrosion resistance on magnesium and its alloys (21). Such treatment provides an excellent base for painting and good abrasion resistance, heat resistance, and protection from atmospheric corrosion. A minor use for ammonium bifluoride is in the preservation of wood (qv) (22).  [c.149]

Atmospheric corrosion is electrochemical ia nature and depends on the flow of current between anodic and cathodic areas. The resulting attack is generally localized to particular features of the metallurgical stmcture. Features that contribute to differences ia potential iaclude the iatermetaUic particles and the electrode potentials of the matrix. The electrode potentials of some soHd solutions and iatermetaUic particles are shown ia Table 26. Iron and sUicon impurities ia commercially pure aluminum form iatermetaUic coastitueat particles that are cathodic to alumiaum. Because the oxide film over these coastitueats may be weak, they can promote electrochemical attack of the surrounding aluminum matrix. The superior resistance to corrosion of high purity aluminum is attributed to the small number of these constituents.  [c.125]

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.  [c.164]

BS2569 Sprayed Metal Coatings. Part 1 Protection of Iron and Steel by Aluminum and Zinc Against Atmospheric Corrosion.  [c.143]

The main factor in causing filiform corrosion is the relative humidity of the atmosphere, and if this is below 65% (the critical relative humidity for the atmospheric corrosion of most metals, see Section 2.2) it will not occur. As the relative humidity increases the thickness of the filaments increases at 65-80% relative humidity they are very thin, at 80-95% relative humidity they are much wider and at approximately 95% relative humidity they broaden sufficiehtly to form blisters.  [c.170]

There are many special factors controlling atmospheric bimetallic corrosion that entitle it to separate treatment. The electrolyte in atmospheric corrosion consists of a thin condensed film of moisture containing any soluble contaminants in the atmosphere such as acid fumes from industrial atmospheres and chlorides from marine atmospheres. This type of electrolyte has two characteristics which are summarised in a paper by Rosenfel d .  [c.230]

The above work is important, since many practical corrosion systems involve a thick but porous film of corrosion products, e.g. rusting, sul-phatising, tuberculation and atmospheric corrosion, and the approach may lead to a more valid corrosion testing technique for these situations.  [c.321]


See pages that mention the term Atmospheres, corrosive : [c.2731]    [c.399]    [c.282]    [c.2124]    [c.1190]    [c.8]    [c.343]   
Plant Engineer's Handbook (2001) -- [ c.975 ]