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Atmospheric corrosion formation

Fig. 4 Important steps during initial stages of S02-induced atmospheric corrosion formation of protons and bisulfite ions in the aqueous layer (a), ligand exchange between a surface hydroxyl group and a bisulfite ion and subsequent weakening of adjacent bonds through proton-bonded neighbors (b), detachment of metal surface center that enters the aqueous phase as a hydrated metal anion-complex (c). (Reproduced with permission from Ref [7].)... Fig. 4 Important steps during initial stages of S02-induced atmospheric corrosion formation of protons and bisulfite ions in the aqueous layer (a), ligand exchange between a surface hydroxyl group and a bisulfite ion and subsequent weakening of adjacent bonds through proton-bonded neighbors (b), detachment of metal surface center that enters the aqueous phase as a hydrated metal anion-complex (c). (Reproduced with permission from Ref [7].)...
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). [Pg.336]

These detailed microscopic studies show that it is possible to predict how and where pitting corrosion will occur on the surface. Like the titanium surface, an aluminum surface is passivated at normal temperatures by formation of an oxide layer in the ambient atmosphere. Despite formation of an oxide layer, aluminum surfaces can also be studied by STM. Pitting corrosion can be observed after 10 h of immersion of an aluminum surface at -1.2 V/normal hydrogen electrode in a IO-2 A/ NaCl electrolyte. The pitting on aluminum is observed as a general roughening... [Pg.279]

Time of wetness (TOW), considered as the time during which the corrosion process occurs, is an important parameter to study the atmospheric corrosion of metals. According to ISO-9223 standard, TOW is approximately the time when relative humidity exceeds 80% and temperature is higher than 0°C. No upper limit for temperature is established. In tropical climates, when temperature reaches values over 25°C, evaporation of water plays an important role and the possibility to establish an upper limit respecting temperature should be analyzed. The concept of TOW assumes the presence on the metallic surface of a water layer however, there are recent reports about the formation of water microdrops during the initial periods of atmospheric corrosion, showing that the idea of the presence of thin uniform water layers is not completely in agreement with the real situation in some cases (particularly indoor exposures). [Pg.61]

Almost all tests carried out to study the starting process of atmospheric corrosion have been performed in a surface without corrosion products however, in real conditions, the metal is covered with corrosion products after a given time and these products begin to play its role as retarders of the corrosion process in almost all cases. Corrosion products acts as a barrier for oxygen and contaminants diffusion, the free area for the occurrence of the corrosion is lower however, the formation of the surface electrolyte is enhanced. Only in very polluted areas the corrosion products accelerate the corrosion process. Water adsorption isoterms were determined to corrosion products formed in Cuban natural atmospheres[21]. Sorption properties of corrosion products (taking into account their salt content-usually hygroscopics) determine the possibilities of surface adsorption and the possibility of development of corrosion process... [Pg.65]

Recent reports about the microdroplets formation in the starting periods of atmospheric corrosion [15-18] show that the idea of a thin uniform water layers is not completely in accordance with the reality. It has been observed that when a water drop is on the metallic surface, formed in the place where a salt deposit existed before, microdroplets are formed around this central drop. The cathodic process takes place in these surrounding microdroplets, meanwhile the anodic process takes place in the central drop. This idea is not consistent with the proposal of an uniform water layer on the surface and it is very probable that this situation could be obtained under indoor conditions. It has been determined that microdrops (about 1 micron diameter) clusters are formed around a central drop. An important influence of air relative humidity is reported on microdrops formation. There is a critical value of relative humidity for the formation of microdroplets. Under this value no microdroplets are formed. This value could be considered as the critical relative humidity. This situation is very similar to the process of indoor atmospheric corrosion presence of humid air, deposition of hygroscopic contaminants in the surface, formation of microdrops. Water is necessary for corrosion reaction to occur, but the reaction rate depends on the deposition rate and nature of contaminants. [Pg.71]

Wang Jia, Zhang Jibiao. The effect of micro-droplets formation caused by the deliquescence of the deposited salt particle on atmospheric corrosion of metals. Proceedings 16th International Corrosion Congress, Beijing, China, September 19-24, 2005. [Pg.90]

The concept of TOW assumes the presence on the metallic surface of a water layer however, there are recent reports about the formation of water microdrops during the initial periods of atmospheric corrosion, showing that the idea of the presence of thin uniform water layers is not completely in agreement with the real situation in some cases (particularly indoor exposures). [Pg.142]

From a chemical viewpoint, the interior of a crystal and its surface can be looked upon as if they were different individuals, comparable to two modifications of a substance or to a metal which is under mechanical stresses. The phenomenon of stress corrosion reveals that the part under tension differs in its chemical reactivity from the part under compression. Different modifications of silica can have very different reactivities. Therefore, it must be expected that the surface film can affect the apparent stability of a solid. Indeed, the surface structures of some hydrated salts are in equilibrium with the ambient atmosphere and prevent these crystals from losing water (efflorescing), even if the bulk of the crystal has a higher water vapor pressure than the atmosphere. The formation of a fresh highly asymmetrical surface may also cause substances to detonate. [Pg.87]

The role of alloying elements in weathering steels consists of the effect of formation of the protective layer of corrosion products increase in mechanical strength and toughness and improved weldability. The protective qualities of the corrosion products on the steel depend on the continuous growth of the adherent, compact, inner layer and on low porosity within the layer. The kinetics of atmospheric corrosion were found to obey the equation,... [Pg.213]

Corrosion in other environments such as organic media and gaseous atmospheres are discussed in the literature. Corrosion in organic media is dependant upon the viscosity and the presence of other chemical reagents. Corrosion in gaseous atmospheres is similar to atmospheric corrosion in requiring moisture and the formation of an electrolyte, which in turn can cause corrosion. The corrosion rate will vary with the type of gas such as N02 or S02 present. [Pg.288]

The results of the experiments suggest that the amount of soluble Zn corrosion product formed can be estimated if the deposition of the precursor gas phase species can be determined. However, the question of what controls the formation of the protective layer has not been discussed. In the next section, a model for the atmospheric corrosion of galvanized steel is formulated in which both the role of deposition and the parameters that control both the formation of soluble and insoluble products are addressed. For the remaining discussion, the term insoluble... [Pg.188]

The accumulation of salts within the concrete pore structure can also lead to the corrosion of reinforcing steel, the fourth form of deterioration identified above. This corrosion is accompanied by an increase in the volume of the steel, which eventually causes the concrete to crack and spall. In discussing the atmospheric corrosion of concrete reinforcements, Skoulikidis (21) notes "The increase of atmospheric pollution Intensifies the corrosion tendency of the reinforcements in the atmosphere. The cracking of the concrete was observed more frequently with an increase of the atmospheric pollution (SO2, CO2, NH3, NOx> etc.) and the acceleration of the corrosion by the formation of a more conductive environment, that also chemically attacks the metals."... [Pg.243]

The corrosion resistance of anodized aluminum is more or less comparable with the untreated aluminum in an acidic and alkaline environment. The formation of pits is decreased under atmospheric corrosion conditions ( pitting corrosion). [Pg.92]

Fig. 10.4 Formation of nitrogen-containing compounds during atmospheric corrosion of iron and... Fig. 10.4 Formation of nitrogen-containing compounds during atmospheric corrosion of iron and...
The model for atmospheric corrosion tmder high chloride concentration su ested by Kamimura et al. [32] is based on the separation of cathode and anode sites under the rust and the thin electrolyte. The pH at the anode compartment is affected by the chloride ion concentration and decreased to 1.5 by the hydrolysis of ferric ions and the formation of P-FeOOH. Chloride ions accumrrlate at the anode site and initiate the oxidation of ferrous ions to ferric ions. Accumulated chloride ions increase ferric ion solubility in the electrolyte and accelerate the hydrolysis of ferric ions, causing the pH at the anode to decrease. Low pH at the metal-electrolyte interface accelerated the formation of P-FeOOH. The atmospheric corrosion process is summarized as follows ... [Pg.460]

Relative humidity leads to the formation of a thin surface film on a metal when exposed to rain, fog, or dew formation. Xu et al. [52] monitored the dew formation process with a specially designed experimental arrangement. The results indicated that dust on the metal surface facUitates dew formation and increases atmospheric corrosion. Atmospheric corrosion requires both a thin film as well as some type of contaminant to initiate. The process of dew formation occurs much more rapidly in the presence of salts on the metal surface. Figures 10.13 and 10.14 compare the development and advancement of the dewing process on a clean and dust-contaminated surface, respectively [52]. Dew formation was monitored on mild steel (i) before dewing (ii) after 2 min (iii) after 4 min (iv) after 8 min and (v) after surfece drying (ambient temperature 13 °C, relative humidity 69). If the d.c. current for... [Pg.471]

M. Jonsson, D. Persson, D. Thierry, Corrosion product formation during NaCl induced atmospheric corrosion of magnesium alloy AZ91D, Corros. Sci. 49 (2007) 1540—1558. [Pg.478]

One of the few impressed current zinc systems in the United Kingdom at the time of going to press is shown in Figure 7.10. There has been some concern about the rise in resistance seen on some systems. This may be due to a build up of corrosion products between the zinc and the concrete, or to treatment of the zinc after application to protect it from atmospheric corrosion. Zinc, of course, is not inert and is consumed by corrosion from the atmosphere and water impingement. The anodic reaction also consumes the zinc and gives rise to the formation of oxides and sulphates at the anode/concrete interface which may increase the electrical resistance between anode and cathode. [Pg.159]

Horton et al. [55] observed that when steels containing Cu and Ni are exposed in industrial and marine atmospheres, the Cu and Ni appear in the mst layers both in the loose outer and adherent inner mst on skyward and ground ward surfaces. Also it was shown by chemical analysis that Ni, Cu, Cr and Mn from weathering steel appear in the mst layer and provides protection. Presence of chlorides in the atmosphere accelerates corrosion of steels leading to the formation of basic Fe ", Fe chlorides and jS FeOOH. Townsend et al. [56] conducted 8-year atmospheric corrosion tests on weathering steel in mral, industrial and marine environments with different heated conditions and indicated that heat treatments have no effect on the corrosion resistance/performance of weathering steels. [Pg.12]

A few simulative studies addressing the processes occurring on the steel surface that cause atmospheric corrosion at sites have been carried out and mechanism of rusting process of WS and MS has been proposed. The aim is to develop an early formation of protective rust on WS by applying various surface treatments using electrolytes and suggesting ways to improve the weathering characteristics. [Pg.129]


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